PINK BOLLWORM OF COTTON IN MEXICO. 47 



taken by the nymphs and adults of three species of small undeter- 

 mined Hemiptera is evidently very high. The attacks on the 

 small pink bollworm larvae from these predators are so important 

 that daily examinations of all food placed in the breeding cages was 

 absolutely necessary. Often one small nymph would destroy the 

 larvae from a large number of eggs during the night. 



The larvae of a lace- wing, Ghrysopa ruftlabris Burm., attacks 

 the newly hatched pink bollworm and also the larger larvae in the 

 flowers. 



Only very rarely is a dead larva found inside a boll. The feeding 

 habits within the green boll greatly reduce the chances of attack by 

 parasites and predators during this period. When the exit holes 

 are cut, or the boll begins to open, or when the larvae are migrating 

 to the ground, they are exposed to these enemies for a short time. 

 This short period of exposure may account for the very few parasites 

 found. Only three species and one specimen of each were found 

 attacking the larvae. They were the Hymenoptera Habrobracon 

 sp., Parisierola emigrate/, Rohwer, and a small dipteron, Tortri- 

 ciopTiaga tortricis Coquillett. The scarcity of these parasites during 

 the two years proves very conclusively that no relief can be hoped 

 for from this source. 



The pupae of the pink bollworm in Mexico were not attacked by 

 parasites, so far as our observations show. 



The small chalcid Trichogramma minutum Riley may prove bene- 

 ficial in parasitizing the eggs of the pink bollworm, but it was not 

 observed attacking the eggs until late in the season, and then only 

 very rarely. 



An outbreak of mites, Pediculoides ventricosus Newport, occurred 

 on the hibernating larvae in the laboratory in 1918. Steps were 

 taken immediately to check them by burning all infested material. 

 To what extent these mites occur in the seed houses was not deter- 

 mined. 



REPRESSION. 



FUMIGATION OF SEED. 



From the known instances in which infestations have occurred 

 from larvae planted in the seed there can be no doubt of the danger 

 of planting infested seed. Several methods of killing the larvae in 

 the seed have been used in Egypt and other places (10), but all 

 fall into three classes: Immersion of the seed in some substance to 

 kill the larvae, treatment with heat, or fumigation with poisonous 

 gases. Immersion of seed in liquids is obviously out of the question 

 where tons of seed are used for planting on a plantation. In Egypt 

 larvae can be killed by exposing them to the heat of the sun. Pre- 

 liminary experiments showed that the temperature in Mexico during 

 the planting season was not high enough to kill the larvae and that 



