Control. So far the best results in controlling the citrus thrips have come from spraying; experiments being conducted in California and Arizona with very good results. Two sprays were used in the work, lime-sulphur diluted at the rate of one part to eighty parts of water, and tobacco extract (40 per cent nicotine) diluted one part to eighteen hundred parts of water. The lime-sulphur causes slight burnings, but otherwise is as effectual and much less expensive than the tobacco extract. Four applications are recommended: the first just after most of the petals have fallen; the second in ten to fifteen days after the first; the third from three to four weeks after the second and the fourth during the months of August or September, when the thrips are numerous on the foliage. In spraying for this insect it is advisable to use angle nozzles and from 175 to 200 pounds pressure, care being taken that every portion of the tree is thoroughly drenched.

THE PEAR THRIPS.

Euthrips pyri Daniel.
(Fig. 32.)

General Appearance. The eggs are very minute, white and bean shaped. They are embedded in the tender tissues of the host. The first born larvæ are white, with distinct red eyes, and move slowly. They are often very thick on the trees and are known as "white thrips.' Pupation takes place in the ground, the pupa being white and seldom met with except by careful investigation. The adult insect is dark in

FIG. 32. The pear thrips (Euthrips pyri Dan.). Adult female and nymph. (After Moulton.)

color, varying from an amber to a dark brown or almost black. The presence of this species is usually told by ravages on the tender tissues of the expanding flowers and leaf buds and later by the attacks on the young fruit. In badly infected orchards the buds often fail to open and the whole orchard may present a brown fire-swept appearance.

The fruit may be scabbed and curled or otherwise deformed by the constant chafing.

Life History.-As stated above, the eggs are inserted in the stem, leaf or small fruits of the host. They hatch in from four to five days, the larva or "white thrips" beginning to feed at once and to do damage. When full grown, which takes from two to three weeks, they drop to the ground and after penetrating several inches enclose themselves in a small cell, where they remain throughout the transforming or pupal period. This period usually begins about September and continues throughout the months of October, November and December, when adult insects are formed. These remain in the ground until February before emerging. The transformation from the larval to the adult stage occupies several months, the slow growth being probably due to the cold winter season.

Distribution. The pear thrips is distributed throughout the Sacramento and San Joaquin valleys, and particularly in the following counties: Santa Clara, Alameda, Contra Costa, San Joaquin, Solano, Sacramento, Yolo, Napa and Sonoma. It has also been reported from the Sierra foothills in Placer County.

Food Plants. This insect is particularly a deciduous tree pest and works great damage upon the leaf and flower buds as well as the young fruit. The initial damage is done just before or after blossoming time. The pear suffers probably more than any other tree due to ravages of this insect, although prunes and plums are also severely attacked. Peaches, apricots and almonds also receive serious damage some seasons. The following are other hosts of this pest: apple, cherry, fig, grape and English walnut.

Control.-*Government Formula. "The formula which has given the best results is made up of the 3 per cent distillate oil emulsion, to which is added from 1 per cent to 13 per cent of tobacco extract No. 1 (black leaf containing 2.75 per cent nicotine) or tobacco extract No. 2 (sulphate of nicotine or black leaf 40), which is 40 per cent nicotine, at the rate of one part to from 1,500 to 2,000 parts of the spray mixture. The distillate oil emulsion may be obtained from several dealers in chemical and spraying supplies, or may be made at home. By the use of the homemade emulsion, a considerable proportion of the cost of spraying is saved and, what is more important, the quality of the emulsion is above reproach, when good materials are properly used in its manufacture."

Whitewash.-Mr. Earl Morris, horticultural commissioner of Santa Clara County, has had remarkable results in controlling pear thrips on pear trees by the use of a whitewash spray. His work covers a period of two years. The trees were sprayed with thick whitewash when the buds were just beginning to open. Some of his results as published in Bull. No. 238, Cal. Agrel. Exp. Sta. are as follows:

"We used eighty (80) pounds of quicklime for one hundred (100)

*From G. E. Merrill, M. B. Cal. Hort. Com., Vol. I, No. 2, p. 54.

gallons of spraying material. The whitewash was strained through a one fourteenth (1-14) inch mesh wire screen and the same sized screen used on the suction hose of the pump. The ordinary Bordeaux nozzles worked well, but it was necessary to enlarge slightly the opening in the disks of vermorel type nozzles. We found it very important to have the lime properly slaked. Good lime properly slaked is of creamy consistency, with a negligible amount of grit. It forms a smooth. uniform, creamy coating on the tree. An attempt to use improperly slaked lime will usually result in complete failure. No amount of written instruction will teach one to slake lime. The knowledge must come from actual work with some one who has had the experience.

In orchard practice we found it convenient to have our slaking vat, which was 1 by 4 by 6 feet, elevated about three feet, with one end slightly lower than the other. In the lower end we arranged a sliding door through which the whitewash flowed by gravity into a containing vat. The lower vat was shorter, narrower and deeper than the slaking vat to facilitate the removal of the material to the spray tank. Between the two vats we arranged a piece of window screen, of one fourteenth inch mesh, supported by chicken fencing, through which the whitewash passed in flowing from the slaking vat.

The cost of material ranges from one (1) to one and one half (14) cents per gallon, depending upon the cost of lime and labor. One application proved sufficient to protect the blossoms and permit setting of fruit. We did not find it necessary to spray a second time for larvæ, although in the first experiment enough larvæ appeared to lead us to believe that in some cases a second spraying would be necessary with some good contact spray."

THE ONION THRIPS.
Thrips tabaci Lindeman.

General Appearance. The adult female is pale yellow in color with an elongated dusky spot on the dorsal surface of the middle thoracic segment. The length of the body varies from 1 to 1.2 mm. The eyes are brown, while the antenna and legs are dusky. The wings are faintly yellowish, their fringes being dusky. The antennæ are seven jointed. The male larvæ are somewhat smaller than the female and of a darker color and often with a greenish tint. The eyes are

red.

Life History.-The life history of this pest has not been thoroughly worked out, but no doubt greatly resembles those previously described. Distribution. This species is generally distributed throughout the entire State.

Food Plants. The onion thrips is especially destructive to onions. grown for seed. It damages the seed buds before the seeds have hardened and in many instances causes a complete failure of the seed crop.

It is also destructive to roses, carnations and other flowers (wild and cultivated), grasses, fruit blossoms and truck crops.

Control. Nicotine extracts or the Government formula as recommended for pear thrips are efficient control methods for this species. The thrips are most active on the outside of the buds early in the morning, so that is the best time for applying a spray. The flour paste as recommended for the bean thrips is also applicable to this species.

HEMIPTERA (Order).

HALF-WINGED INSECTS.

CICADAS, LEAF-HOPPERS, TREE-HOPPERS, PLANT LICE, SCALE INSECTS AND TRUE BUGS.

This is one of the largest orders of insects as well as one of the most destructive known. There are nearly twenty thousand species.

The term Hemiptera comes from the fact that the fore wings of one of the suborders are thickened at the base, the tips being membranous and overlapping, thus appearing like half wings. Not all of the members possess these thickened wings, in fact a great many of them have no wings at all. This is specially true of some plant lice and of the female scale insects. The mouth-parts are formed for piercing and sucking and not for chewing. The metamorphoses are incomplete; that is, the young and nymphs differ from the adults only by the lack of wings in those species having well developed wings, while the young in those individuals not having wings appear almost identical with the adults.

The order Hemiptera is usually divided into the three following suborders: Homoptera, Heteroptera and Parasita or Anoplura, each of which will be considered separately.

HOMOPTERA (Suborder).

This suborder includes insects of the order Hemiptera, all of which, without exception, are very destructive to plant life. Wherever wings are present they are usually membranous and held roof-like over the body when at rest. The front of the head is bent under so as to touch the bases of the fore legs.

The families of this suborder are:

Cicadida (Cicadas).

Fulgorida (Lantern flies).

Membracida (Tree-hoppers).

Cercopida (Spittle insects).

Jassida (Leaf-hoppers).

Psyllida (Jumping plant lice).

Aphidida (Plant lice).

Coccida (Scale insects).

Aleyrodida (Mealy wings or white flies).

The Fulgorida and Cercopida will not be considered here.

CICADIDE (Family).

CICADAS.

The cicadas are well-known insects, being commonly called harvest flies or locusts in the eastern states. The proboscis rises plainly from the head; there are ocelli present; the males have musical organs; feet with three segments and the antennæ are very small and bristle-like. The eggs are laid by the female in small twigs, punctures being made

FIG. 33. The periodical cicada. (Tibicen septendecim Linn.). a, pupa ready to transform; b, old pupal skin; c, adult; d, egg-punctures; e, eggs. (After Riley.)

by the ovipositor for their insertion. The damage is caused by these egg-punctures. The young larvæ hatch within a few weeks and continue throughout their existence under the ground, where they remain for two or more years, depending upon the species: the so-called 17-year locusts requiring about seventeen years in which to transform from the larva to the adult. The pupa stage is passed in a small cell, also in the earth. When ready to change into the adult the pupa or nymph leaves the ground and crawls up some tree or shrub. The back splits and the adult issues. These insects appear in such great numbers during certain years as to become terrible pests, their depredations being known as plagues. There are many species in California, though none of them are as destructive as the 17-year locusts or the periodical cicada of the eastern states.

MEMBRACIDE (Family).

TREE-HOPPERS.

The membracids are rather small insects and generally characterized by the prolongation of the prothorax which covers nearly the entire