304 



INJURIOUS AND BENEFICIAL INSECTS OF CALIFORNIA. 



numerous short tubercles or body projections. The full-grown speci- 

 mens vary from | to \ inch in length. The pupae are at first the color 



of the larva;, but gradually assume that 

 of the adults. They are T 5 o inch long and 

 enclosed in oval, greenish cocoons which 

 are about \ inch long and constructed 

 from the frass and chewed bits of the 

 stalks. They are usually located within 

 the burrows. 



Fig. 2 9 8.— The potato stalk borer, 

 Trichobaris trinotata Say. Larvse, 

 enlarged three times. (Original) 



Life History.- 1 " — The weevils hiber- 

 nate in the burrows within the old stalks 

 of the food plants and emerge in the 

 spring about the time the new plants 

 begin to come up. After mating, the 

 females puncture the tender stalks with 

 their snouts and deposit a single egg in 

 each hole. Upon hatching, the young 

 larvae begin to bore into the center of 

 the stalks, which they proceed to hollow 



out, continuing their burrows beneath the surface of the ground. By 



the middle of May the larva? are full-grown and at once begin to con- 

 struct the pupal cells from bits of the chewed potato stalks. These 



cells are made within 



the burrows. Pupa- 

 tion requires about 



one month and the 



adult stage is reached 



by the middle of 



June. The weevils 



do not generally 



leave the burrows at 



this time, however, 



but hibernate there 



until the following 



spring. Those which 



do emerge remain 



under rubbish or in 



sheltered places. 



There is but one 



brood a year. 

 Nature of Work. — 



The 1 a r y ae make 



their burrows in the 



hrnnnl-ioc. *r>A mo ,'„ Fig '- 299 - — Tne Potato stalk borer, Trichobaris trinotata 



uicuiiucb dim mam Say. Pupae in dead stalks and cocoon removed to show 

 Stalks of the plants, sna P e and texture. Slightly enlarged. (Original) 



causing them to wilt and die, thus preventing the proper maturing of 

 the tubers. In cutting open the infested stalks, the burrows, filled with 

 Trass, and the larva- or pupae may be seen. Fig. 297 shows the nature 

 of the work in freshly killed stalks. 



hese data are for Imperial County only. 



