The Olive Its Culture in Theory and Practice/Chapter 10
Pests
CHAPTER X.
Macbeth. "What! will the line stretch out to the crack of doom!"
Macbeth, Act iv., Scene i.
The writer regrets the necessity of introducing any new pests to his readers, but if we are still spared the visitation of some, time in his course may bring them to us.
The olive is subject to a diversity of maladies, of which some are derived from the action of insects and parasitic plants, others, from meteorological influences, and still others, from improper methods of cultivation, such as excessive or defective nutrition.
The insects which are most harmful to the olive are the following:
COLEOPTERA—Beetles.
Apion Vorax
Mecinus circulatus
Phloetribus oleae
Hylesinus oleiperda
Polycaon confertus |
Twig borer |
HEMIPTERA—Bugs, Lice.
Psylla olivina
Coccus oleae |
Black scale |
Lecanium oleae |
Black scale |
Cisticoccus pollinii
Trips oleae |
Olive louse |
Aspidiotus Conchiformis |
Apple scale |
Aspidiotus Rapax |
Greedy scale |
Aspidiotus Perseae. |
Red Bay scale |
HYMENOPTERA–Saw Flies, Wasps, Bees.
Cynips oleae
Pteromalus quadrum
LEPIDOPTERA—Moths.
Prays oleellus |
Olive moth |
DIPTERA—Flies.
Dacus oleae |
Olive fly |
Of these insects, the most dangerous are the Twig borers, the Psilla, the Moth and the Fly; the scale insects and the olive louse come next.
APION VORAX.
Among the very small insects which damage the olive there are three curculions, two of the Apion genus and a third of the Mecinus.
The first of the Apion kind, has the antennæ, eight-jointed; the first joint is long and conical, the second a trifle shorter, the third still shorter than the second and the remaining five are very short, gradually broadening towards the extremities into a solid pointed club. The rostrum, cylindrical and arched, jaws short, eyes lateral, protruding and round. Thorax conical, body curved and convex, compressed anteriorly.
Winged, shell very small and pointed, shield wing ovoid, larger at the base than the thorax, jaws elongated and truncated, femora puffed out, tarsi spongy beneath, with the first two joints conical, penultimate expanded, heart-shaped and bifurcated, the last cylindrical, enlarged at the extremity and furnished with two hooks.
The insect is about half an inch in length, body blackish, thorax gray on upper part, shield wing ridged with blackish green, sparsely sprinkled with dirty white hair, femora deep yellow, tarsi gray.
The other Apion differs from the one described, by having the first joint of the antennæ somewhat longer, the second shorter than the first, and the other six so short as to be almost globular; the rostrum less arched, the hind legs having a sort of stinger or tooth, The last joint of the tarsi rather long and cylindrical, with the feet very close together. It is entirely black and sparsely sprinkled with whitish hair, and is about half an inch in length.
The third curculion, the Mecinus Circulatus has the antennæ inserted in the middle of the rostrum or proboscis. The antennæ is five-jointed, the first very long and conical, the others transversal and short, the club oval and nearly solid. Rostrum not very long, strong, slightly inclined, cylindrical and not dilated at the extremity. Body oblong, cylindrical and winged. Thorax cylindrical and much compressed in front. Shield triangular, paws or feet, hard and inserted very near together. The shield wing elongated and cylindrical. The tarsi spongy beneath the first two joints, triangular, penultimate expanded and the last one elongated and cylindrical.
This insect is a trifle more than one-twelfth of an inch in length. Chestnut colored with stripes of a lighter shade along the edges of the shield wings and about the head. The feet are dark, as are also the tarsi.
The three above described curculions in their last stage attack the buds of the tender branches, and gnaw the shoots at the forks, digging a nest in which they conceal themselves. Here the female deposits her eggs and the resulting larvæ imitate the habits of the Phlœtribus whose description follows.
PHLŒTEIBUS OLEÆ.
(See Plate IX.)
The egg (Fig. 5) of this insect, is oblong in shape and of a yellowish white color, and a little over an hundredth of an inch in diameter.
The larva (Fig. 6, 7, 8,) at its greatest size is an eighth of an inch in length, is oblong and soft, with callous head; body composed of fourteen rings, one cephalic, three thoracic, and ten abdominal of a dirty white color, with reddish jaws; the palpi, short and small, the antennæ just visible, with a considerable enlargement near the margin of the fore part of the head, the eyes scarcely discernible, placed behind the insertion of the jaws, the thorax fuller than the rest of the body, the upper thorax a little larger than the next two rings taken together, more convex and without the transversal wrinkles of the abdominal rings.
The chrysalis (Fig. 9) ovoid, oblong, with head inclined towards the breast, shield wing fluted and embracing the abdomen at the sides, the feet exposed and drawn up on the ventral part of the body. Antennæ inserted in the front of the head passing below the eyes and the sides of the thorax, folding under in such a way that the end of the proboscis or club reaches to the fore feet. It is a dirty white in color with reddish eyes and jaws.
This insect is distinguished from the Hylesinus principally by the antennæ of nine joints. The first six are simple, the last three are dilated into a three-bladed club (Fig. 11). The body is convex and oval, and of a blackish brown color, and covered with an ashy yellow down. Antennæ and tarsi deep yellow, upper thorax broader than it is long, and unequally speckled; the shield wing is over twice as long as it is wide, rounded at the extremities and covering exactly the abdomen with nine lengthwise flutings delicately speckled; the feet robust and rather short, the femora of a brilliant black in color.
The Phlœtribus count two generations.
FIRST GENERATION.
In the autumn and winter each insect hides itself in a nest dug in the forks of the bearing branches (Fig. 3, 4). In the first days of spring, the insects abandon the nests to mate, after which they assault the dead branches, where the bark is very smooth, and dig a trench in which to deposit their eggs, (Fig. 1, 2,) gnawing obliquely first the bark and then the ring of the wood until they have a road from a twelfth to an eighth of an inch in width, they then retrace their steps, following always the ring of the wood. The female now commences to deposit her eggs singly to the right and left, forming for each a niche which is enclosed by a partition made of bits of wood agglutinated with saliva, and in twenty or thirty days, from thirty to thirty-two eggs are deposited.
Sometimes two females will enter at the same aperture and after the first part of the gallery is completed will bore in opposite directions, often taking the form of a T (Fig. 1. e.) or a Y (Fig. 1. d.)
The working of the insect is manifested by a small tumor or windgall resembling soap foam which issues from the holes made by them on entering. These excrescences are composed of excrement and fibres of the wood mixed with salivary fluid. The eggs hatch in fifteen days from the time they are deposited. The larvae nourish themselves from the fibre of the wood boring secondary tunnels, the first perpendicular, with parallel ones between, resembling much the reeds of an organ (Fig. 1. e.)
The greatest length of a gallery or tunnel never exceeds three quarters of an inch and is less than one-twelfth of an inch in diameter. The number of the lateral tunnels are not usually more than twenty on the same line or thirty on two lines. When the female has finished depositing her eggs she crawls to the external orifice of the gallery and dies.
At the end of thirty or forty days the larva having reached the maximum stage of development, bores into the bottom of its own gallery, an oval niche (Fig. 1. e.) in which it remains immovable and without food for eight or ten days. From this stage it passes into that of the chrysalis casting its abdominal appendage. At the end of another ten days (Fig. 10) the chrysalis becomes a perfect insect which proceeds to gnaw the new wood of the tree, and the bark about its cell, emerging according to the season, in April or May. It flutters for a short time about the tree and then settles down, and bores a hole at the fork of a bearing or blossoming branch, which being deprived of its necessary nutriment soon languishes and dies. In a few days the mating takes place and about the first of June the boring of the tunnels for the depositing of the eggs and rearing the young, follows, as has been heretofore described.
THE SECOND GENERATION.
The offspring of this second generation appear about the last of August and first of September, and prepare a nest as did their predecessors, in the bearing boughs of the tree, where they pass the autumn and winter preparing for reproduction in the coming spring.
The damage from the Phloetribus is considerable. Those of the first generation destroy the blossoms; and those of the second destroy the fruit, as they always attack bearing branches. The drying up of the leaves and fruit on the tree may usually be traced to these insects. Since they are reproduced only in the dry branches or those which are perishing, the best method to impede or diminish their propagation consists in keeping the trees perfectly free from decayed limbs. As soon as a limb shows signs of languor it should be removed and burned.
HYLESINUS OLEIPERDA.
(See Plate X.)
This injurious insect is designated by various names in as many localities. In organization and habits it bears a close resemblance to the Phloetribus. Indeed the egg, larva, chrysalis and insect are nearly identical in form and size. (Fig. 4, 5, 6, 7.)
The larva in this case being a trifle larger and the antennae of the insect having eleven joints instead of nine. The fundamental color of the insect is lighter than that of its thorax. The body is a twelfth of an inch in length. Before the middle of July the Hylesinus has reached its perfect development, and from this time on, its methods are precisely those of the Phloetribus, and its treatment should be the same.
THE POLYCAON CONFERTUS.
This insect is the common twig borer of California, and similar to that found on the oak tree. It attacks the olive early in April, boring in the forks of the young wood. If discovered in time it can, to a great extent, be gotten rid of by shaking the trees both night and morning. The Polycaon is not a very dangerous pest, although, it causes more or less injury to the tree, which may result in the loss of several of the minor branches.
PSYLLA OLEÆ.
(See Plate XI.)
The egg of the psylla is spheroidal in shape, and of a diaphanous white color, a little over a hundredth of an inch in diameter. (Fig. 2.)
The larva (Fig. 3) is a depressed ovoid, oblong, the head bi-festooned in front, the last abdominal ring is very much larger than the others. It is rather soft and of a greenish white color, the eyes red, the extremities of the antennæ and tarsi, black. It is completely covered with a cottony substance which is thick and long on the abdomen, and falls behind in a fringe.
The chrysalis (Fig. 4) resembles the larva in its general appearance, differing from it in the shield wing, which is oval and ridged, covering the sides of the abdomen, greenish in color, with last abdominal ring brown or nearly black, the shield wing of a yellow brown color. The insect (Fig. 5, 6) has a wide head, triangular in shape, the upper part curved in, and square at the corners, with a deep scallop nearly bi-secting the lower part, the eyes oval, placed at upper corners of the head, the antennæ (Fig. 8) six jointed; the last one terminating in two short bristles, the upper thorax very short, the lower thorax large, convex, twice as long as it is wide, and nearly hexagonal. Upper wings or shield wing, oval, rhomboidal, much longer than the abdomen and meeting in a sort of roof at the upper margin of the skull; a sinew, starting from the point of the shoulder, is visible, which bi-sects it. The lower wings are shorter than the upper ones. Abdomen small terminating in a blunt point, and in the female provided with a distinct borer. The feet are short and robust, and the head is of a light green color.
The Psylla counts two generations which succeed each other in the spring, during the evolution of the blossoms. At the commencement of the warm season some of the insects die, while others of both sexes remain through the summer. During the autumn and winter they seek shelter on the under part of the leaves, or stalks of the tender shoots, and shield themselves there as best they may from the storms.
As soon as the olive blossoms in the spring, the mating of the Psylla takes place, and the female deposits her eggs on the flowering branches, enveloping them with a cottony material. The larvæ soon appear, separating themselves at once from the cottony covering, and attacking the blossoms from which they draw their aliment. In twenty days from hatching, they transform themselves into perfect insects. In the warmer localities the Psylla appears about the middle of April, but in very forward seasons it frequently happens that the second generation is at work by the last of that month. The Psylla of the first generation commence the work of propagation at once by attacking fresh branches, and continuing without stoppage, till the first of July. A part of the insects then die, whilst others survive until the succeeding spring. The larva and the chrysalis prefer remaining in the same place; when molested they move with difficulty, and even the insect when disturbed will neither hop nor fly with much agility.
This insect nourishes itself by sucking the honey of the blossoms.
The blossoms attacked by it either wither away, or are slow of development, and produce few olives, and these few of a poor quality.
The early spring rains, if followed by high winds, have a tendency to dislodge the cottony substance containing the eggs or larvæ, and many of them perish in this way, but the radical remedy for their distruction is to cut away the infected branches, although this method is both difficult and costly. All branches pruned away should be burned at once. Another way is to spray the tree, of course before it is in blossom, either with a solution of whale oil soap, and lye, or still better, use high fire test kerosene, mixed with ten times its volume of water.[1]
COCCUS OLEAE.
(See Plate XII.)
The characteristics of this insect are the following:
The egg is orange color, oblong-ovoid in shape (Fig 4). Larva, (Fig. 5, 6,) which hatches in fifteen days from deposit of egg, is very agile in movement, body a depressed ovoid-oblong, composed of eleven rings; one, cephalic, three thoracic which are the largest, and seven abdominal short ones. The antennæ silky and nine jointed, (Fig. 12), the first of which is short and thick, the second very small and the third is the largest of all. After the last abdominal ring there is a wedge shaped appendage and from the posterior angles of this ring start two bristles as long as the abdomen.
The tarsi which forms almost a continuation of the tibia have two joints, the last of which has two small claws and two filaments, ending in buttons. The outlines of the body are fringed with short hair, general color pale yellow, the eyes brown.
When the first shedding takes place the chrysalis becomes fixed and adherent. The body gradually extends iself and the caudal filaments drop away. The figure and transformation varying according to the sex. The male chrysalis after the first moulting has the form of an ellipse, with a ridge running lengthwise the centre of the back, with two other ridges crossing it at right angles. This lengthwise ridge is cut off square near the head and from it spring two other smaller ridges which terminate in eyes. The rings of the body are indistinct, the margins are spread out like a plate, they are rounded at the bottom and lightly fastened together. The antennæ and feet are not visible from a back view. Elevated portions of the body are reddish colored, the expanded portions yellow, and the eyes black.
After some days the second shedding takes place. When the chrysalis has reached its full development it is a little more than a twelfth of an inch in length. Then comes the last transformation, the shell bursts and the perfect winged creature appears. (Fig. 8.)
The female chrysalis differs from the male by having a wider body, and the lateral posterior lobes undivided. It is agile and active. The antennæ and feet extend beyond the margin of the body but in repose are drawn in and cannot be seen from a back view. The segmentary divisions are the same as in the larvæ. When sufficiently developed to reach a twelfth of an inch in length, it assumes an elongated octangular figure. When in motion the feet are not visible beyond the body, the antennæ alone over-reaching it. The back has a ridge running lengthwise, with two other ridges crossing it as has been described in the male. In this stage it is torpid. The last moulting now takes place and it passes to the stage of the perfect insect. (Fig. 9, 10, 11.)
The male insect (Fig. 8) has a slender, elongated body, eyes very distinct, antennæ delicate, thorax well defined, abdomen long, and ending in two filaments twice as long as the body, and furnished with a stiletto shaped appendage. The wings are colorless and transparent and have two thick sinews running lengthwise through them. The body is of a reddish yellow in color and the eyes are black.
The female insect has an ovoid-oblong body with skull and segmentary division outlines evenly fringed. There is a notch at each eye and one at the caudal extremity. The antennæ and feet are concealed by the expansion of the sides of the body. Between the posterior lobes and the anus there is a space triangular in shape, in which by the aid of a microscope, two symmetrical lobes can be seen, and in the center a caudal appendage. The back is of a greenish color marbled with black, the ridge down the center being of a lighter shade.
From a ventral view the rings of the body can be plainly seen, and also the feet, antennæ and borer; all of which are of a pale yellowish green color; the eyes are black. The length is from a fifth to a sixth of an inch.
As soon as the female is perfectly developed, it becomes sedentary, attaching itself to a leaf or the wood of a branch and deposits its eggs, first covering itself completely with a cottony substance, which exudes from its body. In this hiding place it empties itself of from four hundred and fifty to five hundred eggs. The larvæ, as soon as hatched, break through this covering and scatter broadcast, the mother remaining for some time longer, the substance surrounding her hardens and forms a shell which she breaks through and abandons. The time of the metamorphosis is not constant; from May to September, insects, larvæ and eggs can be found at the same time.
This insect draws its nourishment from the sap of the tree, and the branches attacked will wither away. It frequently occurs, that on branches selected by this parasite, the black smut or Rust is generated. Its destruction is not difficult, it only being necessary to spray the tree, at different seasons of the year, with kerosene mixed with water, or some preparation of whale oil soap. Should these remedies be ineffectual, the diseased limbs should be cut away and burned.
The presence of ants on a tree are an indication that these insects are about. The ants are very fond of them and are a valuable auxiliary in their destruction.
LECANIUM OLEAE.
(See Plate XII Fig. 17, 18.)
The larvæ resemble greatly those of the Coccus oleae just described, with this difference in the female; in the adult stage it has the aspect of a tortoise shell, and is of a dark chestnut color, very convex, with the ridge in the middle of the back and the two lateral ones very distinct. As soon as the larva hatches, it leaves its covering and the mother dies. The habits of this insect and the methods for its destruction are the same as given for the Coccus oleae.
CISTICOCCUS POLLINII.
On the branches that are somewhat languid where dried berries and leaves are adherent, can be found in the forks, and at the stem of the leaves, small excrescences, like a grain of corn, the color of the dry wood. On opening one, an outside shell is seen, and in this is a soft heart shaped body or sack which is orange color and enveloping as many as thirty eggs. In April the egg has the germ well developed, and in May the larva appears. It is oblong-ovoid, and has the antennae and feet shorter and more robust than the Coccus oleae just described. The antennae are six jointed and terminating in a group of bristly hair. The femora are very large and on the last abdominal ring there are three short appendages, each terminating in a short bristle. The ultimate transformation of this insect has never been ascertained. The damage done by it however is identical with that of the Coccus oleae, and the proper method of destroying it is to cut off and burn the infected branches.
TRIPS OLEAE.
This insect is also called the olive louse. The damage caused by it is very similar to that previously described.
The larva is soft, oblong, and narrow behind, orange colored, antennae whitish, feet black. The head is square in front, curving in at the top, the eyes protruding, and placed midway the length of the head; antennae short and thick, rings of the thorax large. The abdomen has eight rings which are fringed on the sides with stiff hair. Feet and femora robust, tibia as long as the femora, tarsi short and thick, and like the tibia, terminating in short fine bristles.
The perfect insect has a slender elongated body, head cylindrical, longer than wide, protruding eyes, antennae nine jointed, upper thorax almost hexagonal, wider than it is long, abdomen wider in the middle than at the base, and composed of segments posteriorly rounded, and in the female ending in the ovary, which is nearly horn shaped. Upper wings nearly reaching to abdominal extremities, fringed with long hair, reaching about two-fifths the way round the body, under wings plain and shorter, the feet robust, the femora swollen, the tibia small at the base and enlarged at the extremities, the tarsi short and thick, double jointed and finished with two delicate claws. General color a splendid black, the antennae yellow, the upper wings a dirty white. The length of body nine hundredths of an inch.
The Trips exist in the clefts of the branches and among the buds; and if there are many of them, they will extend themselves to the under-part of the leaves. They are agile and fly well. The female deposits her eggs wherever she happens to be, and the larvæ remain in the same place. About a month is necessary for the different changes to take place. In the spring and autumn they produce several broods. At the beginning of winter, those that survive, conceal themselves under the bark, or in its crevices and rest quietly till the following spring. Then the Trips are in great numbers and invade many branches, the trees infested should be shaken, first spreading a cloth beneath, to gather up the larvae, chrysalides, and winged specimens that may fall. If the branches have been long infected it will be better to take them off outright and burn them. Spraying with kerosene in the autumn before these lice have thoroughly secreted themselves under the bark, will probably answer every purpose,
The Apple, Greedy, and Red Bay Scale insects have all been noticed on the olive in California, but so far as known do not seem to have inflicted much injury on the trees, and are easily exterminated by the application of the usual remedies.
CYNIPS OLEÆ.
This insect has long antennæ which are enlarged slightly near the ends with fourteen or fifteen joints according to sex. The upper wings have three small cubical cells at the base. The borer at base of abdomen is placed between two blade shaped appendages. The female bores into the branches and deposits her eggs. The resulting larvæ gnaws the bark, wood, and even the pith, digging little winding tunnels. The buds on the branches attacked soon wither away.
This insect reaches its perfect development about the beginning of summer. The methods for its destruction should be the same as for the Hylesinus oleiperda.
PTEROMALUS QUADRUM.
This insect has antennæ like an elbow, having nine joints, the first long and the last oval. The head is large and broad, the abdomen of the female prolonged into a conical point. Wings without radiating cells. Tarsi with first joint the longest. Borer scarcely visible. Head a splendid bronze green. Upper wings transparent, without sinews, and with two black spots in each near the outer edge. The Antennæ and feet black. Tarsi deep yellow. Its habits are about the same as the insect just described.
PRAYS OLEELLUS.
(See Plate XIII.)
This formidable enemy of the olive is known as the olive moth. The egg is globular in form (Fig. 7), and its surface is composed of minute tubercles. In color it is milky white, and is about a hundredth of an inch in diameter.
The larva (Fig. 8, 8a, 8b) has a long, soft body, with fourteen rings, one cephalic, three thoracic, and ten abdominal. It has three pairs of true feet in the thoracic rings, and five false pairs in the third, fourth, fifth, sixth, and tenth abdominal rings.
The head is horn shaped, broader than it is long, with a convex bulb on each side. Two indented lines, starting from the base, cross in the middle of the back of the head, and form a V in front.
There are five or six little dots on either side of the head. The antennæ are very small, with three joints. The first thoracic ring is flat and smooth. The second and third have a transversal crease, on each side of which are two minute tubercles, each containing a bristly hair.
The first eight abdominal rings are uniform; they are broader than long, with three tubercles on each side, each holding a bristle. The ninth ring has six hairy tubercles equidistant from each other. The last ring is rounded and shield-shaped in the back, and has two false feet, which are larger than the others, and which project on either side.
When the larva is first hatched, its color is an ashy green, with the head light red. The first thoracic ring contains two brown spots, and the feet are black. As the larva increases in size, these colors become more decided; the head changes to a bright red, the back of the first ring inclines to a pale yellow, and the spots on it become black and nearly square. The last abdominal ring in some larvæ becomes brown, in others not. Subsequently a darker line appears each side of the center of the back, extending from the second thoracic to the ninth abdominal ring. These lines continue to darken, and between them will appear a pale yellow streak. The backs of the first thoracic and last abdominal rings become a straw color. Some larvæ do not change color till after their transformation into the pupa stage. Their greatest length is one-third of an inch.
The pupa is elongated, (Fig. 9, 9 a, 9 b,) and gradually tapers downward in a conical shape, rounded in front; the wings, antennæ, and eyes are visible. In its first days, the color is a light green, but grows darker as did the larva. Its length is about a quarter of an inch. The cocoon which envelops the pupa is composed of silky filaments so finely woven as to be transparent.
The moth (Fig. 10, 10-1, 10 a, 10 b,) has a rounded head covered with narrow scales. Antennæ wiry, with globular joints. Upper edge of upper wings fringed with soft hair, lower edge bare. Lower wings shorter than upper, and fringed all around with hair which is longer on the upper than on the lower edge. Half way the length of the posterior tibia, are two long spurs. Body, antennæ and feet, covered with ashy gray scales. Upper wings a whitish ash color, with a silvery gloss, with a disk-shaped black spot midway the wing, near the lower edge, and another less marked near lower outside corner. The remainder of the wing is dotted with very minute black specks, irregularly placed. The lower wings of a uniform dark ash color. Length, a quarter of an inch, with the wings folded, nearly half an inch with the wings spread. The foregoing is a description of the moth in its tpyical condition and in a state of perfect preservation. The upper wings sometimes vary in the number and size of the spots.
There are three generations of the moth.
First: The winter generation, which draw their nourishment from the leaves and tender buds.
Second: The spring generation, which devours the germ of the blossom even before it opens.
Third: The summer generation, which attacks only the kernel of the seed.
In February the eggs of the first generation are seen on the under part of the leaf (Fig. 1 a a,), In the last days of that month the larva hatches and commences to consume the foliage (Fig. 1 b,) making galleries under the epidermis of the leaf which takes the color of the dry leaf and becomes transparent. Later on, this gallery is burst by the young grub, which continues to prey upon the leaves. (Fig. 1 c,) enveloping itself in silken threads, as a screen against external agents. Some larvæ consume the entire web of the leaf (Fig. 1 d.) and all shun the direct action of the sun. At the end of twenty-five or thirty days (about the last of March) the larva commences its transformation into the pupa, weaving on the same leaf (Fig. 1 e), a cocoon which takes about twenty-four hours. In another twenty-four hours the last change takes place, and they acquire the semblance of the pupa (Fig. 9, 9 a, 9 b.) They remain in a lethargic state for twelve or fourteen days, when the moth appears, which is about the first of April. The moths live a month or more, and from the middle to the last of April they flutter about the olive in the evening when the sun is gone. During the day they remain quiet among the leaves and there the female deposits her eggs.
The larvæ of the second generation hatch in the first half of May and assault the floral cluster, penetrating within the blossom and consuming the pistil and gemmules (Fig. 2 a a). One larva can in this way destroy twenty or more blossoms. In the first half of June they change into pupæ and in seven or eight days after into moths. These live a little more than a month and towards the beginning of July the female deposits her eggs one by one, piercing the calix of the berry. It is seldom that two eggs are deposited in one berry.
THIRD GENERATION.
The eggs which have been deposited in the olive hatch in about ten days, and the larvæ penetrate into the seed of the berry and consume first the skin about the kernel, and eventually the whole almond. (Fig. 5, e, d.) When they have attained their full development they issue from the fruit by boring a hole in the softer part of the seed near the stem, which being thus weakened causes the olive to fall from the tree.
The larva weaves its cocoon at once, on either fruit, stem or leaves. In eight or ten days, that is, from the last of September to the middle of October, the moth of this third generation will appear, from which the generation of the following February will have origin. The damage caused by the moth we have already stated. Those of the first generation injure only a portion of the leaves, those of the second consume the blossoms which would be transformed into fruit, those of the third take the fruit itself.
The different methods that may be suggested to combat the moth may be reduced to these three:
First—To cut away in February and March the branches which shelter the first generation. Their presence can be detected by the appearance of the leaves, which become transparent.
Second— By gathering the olives of August and September as soon as they commence falling, the larvæ at this time being inside the fruit, and the subsequent treatment, in the usual way of oil making, will accomplish its destruction.
Third, The instincts of this insect, as well as others of its kindred, to hover about a flame, can also be utilized as a factor in its extermination. Fires can be built among the trees about sunset, or may be carried in suitable vessels from place to place. Meanwhile the trees should be shaken to dislodge the insects and attract them to the light.
This last operation must be performed either the last of April, from the middle to the end of June, or from the last of September to the middle of October, when the insect is in its last phase as a moth.
DACUS OLEÆ, OR OLIVE FLY.
(See Plate XIV.)
This is perhaps the most injurious to the olive of all insects, on account of the facility with which it multiplies, and the damage it can cause in a brief period of time. We may also add that it is the most common, the most numerous and the most invincible of all its enemies.
The egg (Fig. 9) is ovoidal, elongated in form, and of a milky white color. Length about one-fortieth of an inch. The larva (Fig. 10, 10 a, 10 b,) is conical in form, elongated, and is composed of fourteen rings. The mouth is furnished with two sharp, scaly black hooks (Fig. 10 a,) and on either side the base of the second ring there is a calix-formed papilla, (Fig. 10 b,) the edges of which are scalloped. The twelfth ring is the broadest of all. The thirteenth has small papillæ on each side. The last ring is the smallest and from a back view shows the anus and two lower false feet. The tracheal canals run in a flexuous line to the thirteenth ring where they connect, near the papillæ, with a transversal canal. The general color of the body is a dirty white. The teguments are so transparent that the tracheal and alimentary canals can easily be observed. The papillæ on the second and thirteenth rings are reddish in color. Maximum length a trifle over a quarter of an inch. The pupa is an elongated ovoid in shape. The first and last rings are visible only from a ventral view (Fig. 11, 11 a, 11 b.) The papillæ of the second and thirteenth rings retain their primitive form. All the rings are fluted transversely.
In the first period the pupa is of a dirty white tinge, but changes to a light yellow, the papillae remaining red as does the orifice of the anus. Its length is one-seventh of an inch.
The head of the perfect fly (Fig. 12.), is a little broader than the anterior part of the thorax. The eyes are large and black, antennae three jointed. Its color is sometimes a light straw, and at others a deep yellow.
Of the three joints (Fig. 12 a.), the first is short, the second a little longer, the third twice as long as the second, and ending in a flexuous bristle, longer than itself.
Upper thorax gray, with three lengthwise black lines. Back of abdomen, specked with black, with a lengthwise band, and lower edges of the first two rings a deep yellow. Ventrical, a dirty dark yellow. Wings glossy, with blotches of brown in apex, sometimes another blotch on lower edge, at the extremity of the anal nerve.
The roots of the wings are a pale yellow. Feet light, tarsi a little darker. The borer and ovisac (Fig. 12 b.) is about the same length as the abdomen, and is a dark red. The point of the borer is black. The male differs from the female by the absence of the borer, and by having the posterior margin of the third abdominal ring fringed with black hair turned backwards. The body is one-sixth of an inch in length.
The date of the most copious hatching of these insects is variable. When the olive has reached its greatest development (about the end of July) the flies just transformed from the pupa appear. Copulation then takes place, and the female, choosing the ripest fruit, deposits her eggs there, usually one egg to each berry. (Fig. 1 a. c. b.b).
In less than twenty four hours an amber spot will appear on the surface of the olive where the egg was deposited, which will turn darker after a little time. The spots can be seen only when the berry is green, as it grows ripe they are hardly discernible. Each female deposits about one hundred eggs. In ten or fifteen days these eggs hatch. The larva, with the hooks of borer, attacks the pulp of the fruit, and then makes its way into the seed, boring a winding tunnel. The pulp of the berry above the tunnel will become reddish wrinkled and transparent, thus showing the presence of the enemy. The larva lives from thirty to forty days. Some change into the pupa form inside of the seed and also into flies, but the greatest number abandon the berry by making an aperture through the pericarp and change into pupae either in the ground, or in the crevices on the trunk of the tree.
The flies appear after thirty or forty days. The duration of the three periods, that is the egg, larva and fly may vary as much as twenty days from the foregoing, as eggs deposited at one time may be hatching for twenty days consecutively, and eggs, larvae, pupae, and flies can be found at the same time.
The pupae of the last generation do not change in the given time, that is in thirty or forty days but remain in that state through the spring till the fruit has reached some size and the prosperity of their offspring is assured. Then the fly appears; it usually lives from twenty to thirty days on the trees, passing from branch to branch and sucking the sap wherever found. It is rather torpid during the cool weather but very agile when it grows warm.
The damage caused by this fly consists in the consumption of from one-third to one-half the pulp of the berry, thus diminishing the yield of oil and in leaving inside the seed a mass of excrement, which deteriorates its quality.
There are three expedients for combating the olive fly:
First—To gather the fruit as soon as it is barely ripe, and crush it at once,—thus destroying the larvæ and pupæae within and preventing further multiplication. The localities most afflicted by these pests are those where the harvesting of the olive is protracted through the winter and part of the spring, either from lack of sufficient help, or to make the white oil, as is done in Lucca and on the Riviera. These, in fact, are the regions devastated most frequently by this fly.
Second.—To keep the trunk of the tree clean and to spray the trees after the harvest is over with something strong enough to kill the pupae, and taking care that not even one berry remains on the ground.
Third.—To cultivate the ground well about the tree, after first shaking it and thus to bury all olives containing eggs, larvae, or pupae. The fruit when picked should not be kept in heaps, or the heat engendered will cause the flies to hatch immediately.
This closes the list of insects that are known to prey upon the olive. Some we already have with us, others a close degree of scrutiny may reveal, and still others let us hope we may ever be spared.
PARASITIC PLANTS OR VEGETABLE ENEMIES.
The olive tree is also subject to injury from the action of several parasitical plants of which the principal and best known are the following.
AGARICUS MELLEUS.
(Root rot.)
This fungus has a flat, thin, scaly top with a fluted expanded margin and spongy stalk. On first appearing, it is whitish, but afterwards becomes mottled with red. Spore a floury white. The hairs which are found on the head are black. It is found at the base of coniferous and fruit trees as well as the olive tree.
Its vegetable system is wrapped about the subterranean part of the tree, and its presence can be recognized by an abundant discharge of resinous matter on the trunk and principal roots, especially of coniferous trees, and by a white creeper which develops beneath the bark of the roots and trunk, and by brown filaments resembling fibrous roots which spread out and run over the ground.
The creepers which are first seen are produced from the germination of the spore. Developing from this, the parasite shews itself on the roots, in the form of a filament or creeper, the outer covering being smooth and dark, while the pith or marrow is white. These creepers take root in the wood, penetrating the pith and spreading out until in the form of a membrane, they fix themselves in the regenerating zone. By some writers this root rot has been given the name of Rhizomorpha subcorticallus. In a fresh state it has an agreeable odor and seen at a distance in the dark it has a phosphorescent appearance.
The regenerating zone attacked by the Rhizomorpha ceases to be prolific as the formation of new wood has been interrupted.
The cellular and fibrous elements invaded by these tendrils turn brown.
After this plant has devastated the lower part of the trunk of the tree, it spreads upward to the surface of the ground, showing itself in the autumn through crevices in the bark. The decay of the Mulberry, Chestnut, Fig, and sometimes citrus trees, it is believed is principally due to this fungus. The tree withers gradually without apparent cause, the climate and chemical or physicial conditions having no part in its decline. The propagation of this disease through the creeper, can be effected by the contact of healthy with infected plants. Infection through the spores commences in the trunk, and is transmissible by the wind.
Where this malady is suspected, if it exists, an examination will show the fungoid growth of the Agaricus melleus. The only radical treatment for this parasite is to uproot the infected trees at once, and burn at least the affected parts. The extirpation of the mushroom will prevent propagation by spores. Other trees should not be planted immediately in ground from which diseased ones have been removed.
FUMAGO OLEÆ, BLACK SMUT OR RUST.
(See Plate XV.)
This is an epiphyte fungus which attacks the branches and foliage of the olive more especialty on the under parts. (Fig. 1.) It consists of black sooty blotches which form an incrustation more or less dense, which is smooth on the adhering side and scaly on the outer side. The black powder, greatly magnified, is seen in (Fig. 2.) The trees attacked by this black smut, languish as it impedes the exhalation of the leaves. It manifests itself mostly on plants that have not sufficient light, or which are situated in soil that is poor, or low and humid. Sometimes it follows immediately the invasion of the scale which have enfeebled the branches or where the Honey dew prevails. These are conditions favorable to this fungus.
Some entomologists claim that the scale is the cause of this fungus. This is a question in olive culture that has been widely discussed and has occupied the attention of European experts for the last hundred years with the result that it may now be stated positively that this fungus can be propagated without the aid of the scale insect. The black scale and the black fungus are two separate and distinct pests to which the olive tree is subject and though they are often seen together, have origins entirely distinct.
The black fungus is due solely to local causes. There is either too much dampness or not enough light. The infected branches should be cut off and burned and the tree sprayed with kerosene as heretofore described. No olive tree on ground high enough for a sufficiency of air and ventilation was ever afflicted with this pest. The cultivation of the soil provokes moisture and stimulates the vegetable growth of the tree, so where the black fungus appears, cease this cultivation, do not stir up the soil, but on the contrary check the excessive growth and humidity, by allowing the surface of the ground to harden. Prune the trees so that each may have a maximum of light and air. If the excess of moisture cannot be remedied by these means, the soil must be drained.
VISCIM ALBUM, MISTLETOE.
The mistletoe is propagated from one tree to another by its seed. It extends its green roots through the branches from which it draws its nourishment, greatly enfeebling the tree. The only method of destroying it is, to cut off the branches on which it has effected a lodgment, and burn them.
LICHENS AND MOSSES.
It is erroneously claimed by many writers that the mossy substance which grows upon the trunk and branches of the olive and other trees is a parasite. Instead it is composed of moss and lichens, the principal ones of which are Parmelia, Lecanara, Verrucaria, etc., among the lichens, and Hypsum, Leskea, Bryum and Orthotrichum among the mosses.
These last are cormus fungi, and all are epiphytes and live on the outside of the dead bark and exercise no parasitical influence. They shield the bark from the sun, but the humidity they engender is a frequent cause of rot, and they also serve as nesting places for hurtful insects. For these reasons it is well to liberate the trees from them by scraping the infected parts, or spraying with a solution of lime.
HONEY DEW.
The Honey dew consists of a gummy sugary perspiration on the leaves, especially on the under side, on the flowers, and on the young branches. This substance sometimes forms itself into a varnish uniform in its deposit, and at others into drops like dew. This disease attacks the Olive, Poplar, Linden, Orange, Walnut, Willow and Elm trees and also the grape vine. The real cause of it is unknown. Some writers think that the viscous matter is exuded from the cochineal insect which infests the plants, but others have observed that this disturbance exists both on trees in the open air, and on those enclosed in greenhouses where there were no insects.
The popular idea is that the humor emitted by the morbid leaves is a production of the plant itself, caused by the unfavorable influence of a hot, dry soil. Admitting this to be the probable cause, the remedy would be copious fertilizing and to prune the tree so as to keep the top in proportion to the spread of the roots.
SCAB.
The scab manifests itself in wart-like excrescences as large as walnuts, often affecting the youngest and most slender branches. The plant impoverished by this pest takes on a languid appearance and sometimes dies. Ordinarily this evil is met with on soil that is low or too rich and not sufficiently ventilated, or where trees are placed too near together, in trees excessively pruned, or in those maltreated in the gathering of the fruit by beating with poles.
Some writers hold the opinion that the scab is caused by either a vegetable or animal parasite, but the most diligent microscopic observations have never revealed the presence of an insect, either before, after, or contemporaneously with, the apparition of the small protuberances. The cause therefore must arise from some disturbance of the functions provoked principally by contusions, either from hail storms or by poles in beating down the fruit, by excessive pruning, or by absence of light and air. The contusions of the cortical tissues and of the regenerating zone has the same effect that the puncture of an insect would, and at times produces the enlargement of the zone and sometimes the enlargement of the herbaceous tissues. These enlargements in time extend to the wood under the bark and cause the bark to draw away thus affording a receptacle for different insects. This would however be an effect and not a cause of the evil.
Some orchardists remove the protuberances by shaving them off with a sharp knife, but this does not restore the tree to health as this cutting does not remove the primary cause. The first method for its cure is to keep the trees wide apart, well lighted, to prune sparingly, and to abolish the barbarous usance of beating the trees when gathering the berries.
Senor Tablada says he found an insect eight hundredths of an inch in length in the act of making these warts and cured the tree by cutting them off.
THE OLIVE ROT.
(See Plate XVI.)
The rot is the gangrene which appears on the trunk and larger branches of the olive tree. At times it is so extensive as to consume nearly all the cylindrical part of the wood leaving the larger branches hollow and rendering them an easy prey to the action of the winds.
When a wound is made on the olive tree either by the breaking of a limb or by pruning, and is not at once shielded from contact with the air, a process of canker is initiated, provoked by the humidity found there, the action of insects and the spores of certain lichens or creepers. Trees improperly pruned are usually the ones attacked by the rot. To prevent it, an olive orchard should be placed on well drained soil and receive plenty of light. The trees should not be bruised and when a branch is cut off the wound should be immediately covered with grafting wax or a mixture of cow dung and clay. When the rot has taken hold the diseased part should be cut away till the sound wood is reached and this should be well spread with grafting wax.
INSECTICIDES.
If the orchard is sprayed once a year it will be sufficient, and the best time is in the winter after all danger from frost has passed. Whale oil soap is an excellent remedy but it has not the efficiency of kerosene. It will kill the coccids but has no effect upon their eggs. Kerosene pure and simple would be a dangerous and entirely unnecessary remedy to use, but diluted ten times with water it becomes much less expensive and by far the most efficacious.
The United States Department of Agriculture has published the following recipe to make thirty gallons of wash.
| Kerosene, 2 gallons | 67 per cent. | |
| Whale oil soap, ½ pound | 33 per cent. | |
| Water, 1 gallon |
Boil the soap in the water till entirely dissolved then add it to the two gallons of kerosene, and churn the mixture thoroughly for five or ten minutes. The emulsion if perfect forms a cream which thickens on cooling, and should adhere without oiliness to the surface of glass. Any danger in the use of kerosene lies in the faulty or half-made emulsion. The soap may be of insufficient strength through exposure or some similar cause, when an increase will oblige the oil and water to emulsify, and will also make the emulsion nearly permanent.
The percentage of kerosene should not exceed eighty per cent., as the oil weighs six and a half pounds to the gallon, while water weighs eight, and more cannot easily be held in suspension in water. On the other hand in the process of emulsification, kerosene loses a portion of its value as an insecticide, and emulsions containing less than thirty per cent. of oil, although they may not separate when diluted with water, are nevertheless too much weakened for effective use against scale insects.
The reason that high fire test kerosene is recommended as an insecticide is, that the lighter oils with which it is associated in a crude state, have been eliminated by the refining process, these being exceedingly deadly to vegetation, leaving the refined kerosene which should always be used for this purpose. The heat of the sun increases to an injurious extent the action of kerosene, and stronger solutions than that above given if used at all, should be applied on cloudy days or in the evening.
Experiments with different grades of refined oil, the Elaine amongst the number, show that they all emulsify equally well if the alkali contained in the soap is of sufficient strength. But the Elaine separates the soonest.
The kerosene wash should be applied in a fine spray from the center of the trees, and not the least of its recommendations will be its very great economy.
In addition to insect pests and vegetable parasites, the olive tree numbers among its enemies the blackbird, the robin, the starling, the jay, and the crow, as they are all eager devourers of its fruit, but it is aided and greatly assisted by the nightingale, the titmouse or tomtit, and the woodpecker, as they never touch the berries, and are insect eaters only, and should therefore be encouraged in the orchard. The predatory birds should be fired at in the air, so as not to wound the trees with the shot. The pugnacious English sparrow, by driving away all other birds, especially the little tomtit, is an enemy particularly to be marked for destruction.
- ↑ Kerosene is given the preference as a wash for olive trees, but care should be taken that the quality is first-class. It should be carefully experimented with before being used, in order to see if it will hold the water in solution, for if it does not, it may result in killing the trees. See Mr. Ellwood Cooper's relation of his experience, before the Fruit Growers' Convention, held in Santa Barbara, April 12, 1888.