577 



and may extend over from one to three weeks. Only the nymphs of 

 the last two instars can adapt themselves to a change of food-plant. 

 This fact offers a suggestion in the control of the species. Since the 

 adult is not affected by change of food, migration takes place entirely 

 in this stage. The most effective enemies of the leaf -hopper are its 

 egg parasites, two species of which, viz., Gonaiocerus gibsoni and Ahhella 

 auriscutellum, have been reared. Abbella (Brachistella) acuminata and 

 Ufens niger, also parasitic in the eggs, have been found in Florida. 

 Reduviolus ferus and the ant, Pogonomyrmex barbatus, are predaceous 

 upon the adult. A fungoid disease caused by Empusa grylli frequently 

 attacks this species. An artificial control measure consists of cutting 

 or otherwise removing broad-leaved grasses, which afford the summer 

 food. The ground should be broken up and planted as soon as possible 

 after harvest. If immediate planting is not practicable, all native grasses 

 should be kept down by replougbing. Direct treatment consists in 

 the use of the hopperdozer, formed from a sheet-iron strip coated with 

 coal tar. The apparatus is drawn over the grass, the insects falling 

 upon the tarred surface, and it can be used with advantage while the 

 grain is short. Where the pest is infesting grass land, close cutting 

 while in the egg-stage is advised ; this would prove beneficial in the 

 Northern States, where the egg-stage lasts several weeks. The burning 

 of grasses in which the insects may be hibernating would destroy 

 many of the adults. 



Kelly (E. 0. G.). A New Wheat Thrips. — Jl. Agric. Research, 

 Washington, D.C., iv, no. 3, June 1915, pp. 219-224, 1 plate. 



Prosopotkrips cognatus, Hood, frequently becomes injurious to wheat 

 in localised areas, but has not yet been found attacking oats or other 

 grain crops. It occurs in Kansas, Oklahoma, Missouri, and southern 

 Nebraska. The female cuts the tissue of the young leaves of wheat or 

 grass, usually on the ventral side, and places a single, minute egg in 

 each puncture. The hatching period varies from 6 to 10 days. 

 The full-grown larva is green in colour and measures from about 1 mm. 

 to 1-2 mm. in length. The larval stage lasts from 10 to 12 days, and 

 the larva then crawls down the plant into the soil, where it pupates. 

 There is no indication of the yellow colour of the adult when the 

 larva enters the soil. The complete life-cycle from egg to adult 

 requires from 30 to 35 days. The adults emerge from their winter 

 quarters as soon a? the warm days of spring arrive. Although 

 the length of life of an adult has not been definitely determined, 

 a few have lived 8 months in the laboratory. There are four to 

 five generations a year. These overlap each other, so that adults 

 and larvae are present at all times, even in late winter. The larvae 

 are most numerous in the spring, late summer and late autumn. They 

 feed until the cold weather causes them to hibernate. During the 

 interval between the wheat harvest in June and the sprouting of self- 

 sown wheat in August, the thrips feed and reproduce on Agropyron 

 smithii, Elymus canadensis, E. virginicus, Syntherisnia sanguinalis, 

 Panicum crus-galli and Hordeum jubatum. They are found on these 

 grasses all the year round, but more especially during the period 

 mentioned. The injury is confined to the leaves of young plants, 

 unfolding heads and newly formed grains of wheat, and the young 

 (C208) B 



