April IT. 1902. 



The Weekly Florists^ Review* 



739 



weeds are entirely free from them. They 

 are very active little creatures, and leap 

 and fly readily when disturbed. They 

 vary somewhat in habits, the injurious 

 forms being most destructive to culti- 

 vated flowers and vegetable crojis, al- 

 though a few do damage also to grain 

 and grasses. Some forms may be found 

 under the bark of trees and shrubs, while 

 a few are said to be beneficial by feeding 

 upon other insects. 



greenhouse plants it is known to do more 

 or less injury to nasturtium, mignonette, 

 candytuft, four o'clock and rudbeckia. 

 The most serious injury, however, in 

 greenhouses appears to be to carnations 

 and cucumbers. The damage is often 

 great, sometimes amounting to the de- 

 struction of entire crops or plantings. 



The general appearance of both sexes 

 of this thrips, which are very similar, is 

 shown in Fig. 1 a, highly magiiifled. It 



Fic. 1— Thrips tabaci: a. adult: b. antenna of same: c. young larva; d. full grown larva- 

 enlarfied (from HoAvard, U. S. Dept. Agriculture). 



•The word thrip is sometimes used, but tbis is 

 erroneous, as the form is .the same fer singular 

 and plural, "thrips". in which respect this 

 name is similar to species, sometimes incorrectly 

 pronounced "specie" in speaking of a single form 

 of insect. It recalls the case of the Irishman 

 who indignantly exclaimed to his spouse that 

 she was a disgrace to her '"sek entoirely. " 



The term thrips is also mis-used in England 

 and to some extent by American florists, for ex- 

 ample, to the leaf hoppers of the grape, part- 

 icularl.v when grow n under glass. These are en- 

 tirely distinct, and belong to a different class 

 from the true thrips. 



Life histori/. — Owing to the numbers of 

 species of thrips it is difSeult to formu- 

 late a life history that would fit them 

 all, and to generalize without knowing the 

 habits of the more important groups. 

 The follo.wing, therefore, is merely ap- 

 proximate. 



The parent insects are usually found 

 on the lower sides of leaves or imbedded 

 in flowers of various kinds. In their at- 

 tacks they induce the withering of the 

 parts affected. The females cut by 

 means of a tiny saw with which they are 

 provided near the end of the abdomen a 

 slit in a leaf or stem, usually, and in this 

 deposit an egg, generally inserting it un- 

 der the epidermis till concealed from 

 view. Here the egg hatches in a few 

 days, the young thrips working their way 

 out and beginning to feed. They also 

 suck the juices of plants in the same 

 manner as the adults, and as they feed 

 continuously their growth is rapid. In 

 from one to two weeks, depending upon 

 the temperature, they become full grown. 

 They then cease feeding and seek a spot 

 in which to transform to the final stage 

 of the nymph, and from that stage to the 

 adult. The entire life cycle from the 

 time of the deposition of the eggs until 

 the maturing of the adult has been found 

 to l)e passed under the most favorable 

 conditions, that is, in a warm atmosphere, 

 in three weeks. Half a dozen or more 

 generations may be produced in the arti- 

 ficial atmosphere of a greenhouse during 

 a season. 



THE ONIOX THKIPS. 



(Thrips tabaci Lind.) 

 One of the most destructive forms in 

 America is generally known under the 

 name of the onion or tobacco thrips. It 

 is not alone a pest in the conservatory, 

 but injures a great variety of field and 

 garden crops to which it is more destruc- 

 tive than to plants grown artificially. Be- 

 sides onion and tobacco it affects among 

 crop plants, garden leek, parsley, cab- 

 bage, melon, cucumber, squash, turnip, 

 cauliflower and strawberry, while of 



is pale yellow, with the thorax somewhat 

 darker. The wings are still paler 

 yeUow, with dusky fringes and bris- 

 tles. A full-grown nymph or young 

 is shown at d, and a younger one at c. 



The onion thrips is a comparatively old 

 pest in America, as there are records of 

 its having been injurious as early as 

 1857. In 1872 it attracted considerable 

 attention in Massachusetts, injury to 

 onions in Essex county alone being esti- 

 mated at $10,000 during that year, or 

 about one-tenth of the crop. In 1887 its 

 occurrence in Bermuda on onions was 

 noted, and in later years it did consid- 

 erable damage to this, one of the staple 

 crops of that island. 



The earliest establishment of this spe- 

 cies in South Russia, where it has been 

 stated by its describer to cause much 

 damage to tobacco, affords evidence of 

 its being native to the Old "World, and 

 there is little doubt that it was iijtro- 

 dued in this country from Europe, from 

 which country it was doubtless imported 

 either with green onion tops or on cab- 

 bage leaves which were brought ashore or 

 perhaps thrown overboard while the ships 

 which brought these vegetables lay in 

 our harbors. From the point of introduc- 

 tion, which appears to be Massachusetts, 

 the species has now spread, following 

 the trunk lines of railroads more or less 

 closely, until now it has reached the Pa- 

 cific. Injury has been most severe in tllfe 

 north. 



THE GREENHOtl.SE THRIPS. 



(Heliothrips haemorrhoidalis Bouche.) 

 The species to which the name of 

 greenhouse thrips has been given is of 

 about the same size as the preceding, 

 dark brown, or black in color, with the 

 exception that the end of the abdomen 

 is blood red, whence the scientific name. 

 In its life economy it differs little from 

 the onion thrips so far as is known, and 

 is perhaps of somewhat less importance 

 as an enemy to cultivated plants. Its 

 principal injuries, at least in the United 

 States, are to different species of palm, 

 fern, azalea, rubber plant, and some 

 other conservatoiy plants. It is recorded 

 from Massachusetts,- Pennsylvania and 

 Florida, and this implies a somewhat 

 wide distribution along the Atlantic sea- 

 board. It is more abundant in Europe, 

 but many have been introduced from the 

 West Indies or Central America, and, as 

 with most imported species, it will prob- 

 ably increase in numbers and destnic- 

 tiveness mth time. 



THE WHEAT THEIPS. 



(Thrips tritici Fitch.) 

 This is the most abundant of all thrips 

 occurring in the United States. It is 

 also the most nearly omnivorous, but, for- 

 tunately for the florist, it is not so fre- 

 cjuently found upon plants growing under 

 glass, and the fact that it has such a 

 wide range of food plants is in its fa- 

 vor, as attack is thus distributed and 

 only few forms of cultivated plants are 

 as a rule severely injured. In the time 

 of Fitch, who described this species in 

 1856, it was most abundant on wheat, 

 whence the above name. The strawberry 

 is also severely injured, and Prof. A. L. 

 Quaintance is authority for the statement 

 that during the years 1897 . and 1898 

 this species reduced the yield of 

 that fruit in Florida quite one-third. It 

 is also called the strawberry midget or 

 thrips, and has been reported as doing 

 some injury to orange, cotton, apple, 

 pear, plum, pea, parsley, endive, black- 

 berry, dewberry and roses. In the at- 

 tack upon roses it causes what is termed 

 "blighting," the petals are chafed so that 

 the rose soon blackens and withers. The 

 bud may become infested as soon as it 

 is open sufiiciently for the entrance of 

 the thrips, and in less than twenty-four 

 hours it may be blackened so as to be 

 worthless for market. 



The male of this species measures 

 about .03 inch, and the female between 

 .04 and .05 inch. The species is yellow, 

 with the thorax tinged with orange, and 

 the antennae or feelers are ringed with 

 a dusky color. This insect is probably 

 indigenous to the United States, as we 

 have no information of its occurrence 

 abroad, and it is distributed from Can- 

 ada to Florida, and westward. 



THE CESTRUM THRIPS. 



(Heliothrips cestri Perg.) 

 The present species remained unknown 

 to science until 1895, when it was de- 

 scribed as a new species by JMr. Th. Per- 

 gande, of this office, who is about the 

 only person who has made observations 



Fig. 2— Thripa tritici: a. adult thrips: b. antenna: 

 c. leg— a, much enlarged: b and c highly mag- 

 nified (from Hubbard, U. S. Dept. Agr). 



of any importance in regard to it. He 

 has been familiar with this thrips since 

 1884, when he found it attacking Oestrum 

 nocturnum from Massachusetts. About 

 the same time a specimen was received 

 from Helsingfors, Finland. 



This species measures about 1.2 mm. 

 It is dark brown or black, the end of the 

 body is more or less distinctly reddish, 

 the head reddish, and the eyes dark 

 brown. The fringes are dusky, and the 

 third joints of the antennse are almost 

 as long as the two following joints com- 



