58 



DECIDUOUS FRUIT INSECTS AND INSECTICIDES. 



THE LARVA. 



The thrips larva (fig. 15) is white, with red eyes; it moves about 

 slowly and does not jump, and, being without wings, it can not fly. 

 It does not spin a web, but seeks a sheltered place between rolled or 

 folded leaves or in blossoms, or it lies close along the veins on some 

 of the larger leaves. It reaches full growth after two or three weeks, 

 drops to the ground, and penetrates into it for several inches, where 

 it incloses itself in a tiny cell and here remains during all the rest of 

 the year. 



Larvae do not walk down the larger branches or tree trunks to get 

 to the ground, but drop down or are carried 

 within the old falling calices, or are more 

 usually thrown down by winds or rains. It 

 has been observed that a very large percent- 

 age of the thrips which are thus thrown from 

 the tree are not fully grown. Only those 

 which are mature are able to penetrate the 

 ground and form their cells; the others die. 

 Larvae are scattered everywhere under the 

 trees, and if the trees are large and have inter- 

 mingling branches the thrips are distributed 

 over nearly the whole surface of the soil. 



The period during which larvae are entering 

 the ground begins about April 1, and is at its 

 maximum from about April 10 to 30, practi- 

 cally all thrips having entered by May 15. 

 This period of entering the ground by larvae 

 in Contra Costa County corresponds very 

 closely to the San Jose record as given above. 

 It may be a few days earlier in the warmer 

 sections at Suisun, in the Vaca Valley, and 

 along the Sacramento River. 



Larvae penetrate the loose top soil and 

 usually remain in the 3 or 4 inches of harder 

 ground immediately below the surface. They penetrate to a 

 much greater depth where the soil is loose, owing to shallow 

 spring cultivation, than where it is firmer. If the thrips are 

 disturbed during their first few weeks in the ground — for example, 

 by cultivation — and if not killed, they immediately go deeper and 

 make new cells. The larvae remain in a dormant condition, in 

 which no food is taken, and do not move from their cells, unless 



Fig. 15.— The pear thrips: Larva, 

 Much enlarged. (Author's illus- 

 tration. ) 



