THE IMPORTED CABBAGE WEB WORM. 33 



almost without exception, ignorant of methods of control, and as a 

 result much of the crop is injured and the growers become discour- 

 aged and plant other crops which are less damaged by insects. 



Among these insects are the common cabbage worm (Pontia rapce 

 L.), the imported cabbage webworm {Hellula undalis Fab.), cut- 

 worms {Agrostis crinigera Butl.), a looper (Autographa precationis 

 Guen.), the diamond-back moth {Plutella maculipennis Curtis), the 

 jeet army worm (Caradrina exigua Hiibn.) , the cabbage aphis {Aphis 

 brassicce L.), the spinach aphis {Rhopalosiphum dianthi Schrank), 

 and a number of minor pests. Among the latter is a leaf -miner 

 (Agromyza diminuta Walk.), an unidentified species of thrips, and 

 the melon fly {Dacus cucnrbitce Coq.). The larvse of the melon fly 

 work in cabbage which has previously been injured by the larvse of 

 Hellida undalis. This fruit fly is an exceedingly destructive enemy 

 of cucurbits, and its occurrence in cabbage is rather uncommon. 



The operations in Hawaii occupied a period of about seven months 

 (July, 1910, until February, 1911), and during this time the insects 

 affecting cabbage were kept under fairly constant observation. Dur- 

 ing this period the imported cabbage webworm apparently caused 

 more damage to cabbage than any other insect. The growers claim, 

 however, that from January to April the common cabbage worm 

 {Pontia rapce L.) is the most troublesome pest. During the period 

 of actual observation, however, the webworm appeared to outrank 

 the other species in destructiveness ; in fact, at least a few of the web- 

 worms could be found whenever a search was made for them, although 

 cabbage and turnips were the only crops which were noticeably 

 damaged. The most serious infestation observed in 1910 occurred at 

 Wahiawa : Oahu. On October 10, in company with Mr. E. M. Ehr- 

 horn, a visit was made to a grower at Wahiawa, who planned to grow 

 about 7 acres of cabbage that season. At this time he had three seed 

 beds containing thousands of small cabbage plants. In one bed many 

 plants had been killed, and of those which remained fully 75 per 

 cent were infested by webworms and were worthless. In the other 

 two beds in another field, at a distance of about 200 yards from the 

 first, about 10 per cent of the plants were infested. The larvse in the 

 seed beds were all small. On large cabbage plants in a garden, a 

 mile or more from the seed beds, full-grown larvse were found in 

 moderate numbers. One moth was observed, but no eggs were seen. 

 In small garden patches at this place the Japanese killed occasional 

 larva? which lived in folded leaves or between two leaves, by crush- 

 ing them with the fingers. Apparently only larva? of conspicuous 

 size were found, and as the majority of the webworms mined into the 

 plants, beyond the reach of hand-picking, this method of control 

 seemed of doubtful value. 



