34 



Trelease^ observed more than thirty 3'^ears a^o that during- dry 

 weather, and on the drier situations of the field, ants were much more 

 abundant and hostile to bollworms than during rainy weather, or on 

 the lower and more moist parts of the field. Several observers have 

 advanced the theor}^ that the absence, during dry seasons, of both 

 the boll and cotton worm is largel}'- due to' the effectiveness of several 

 species of ants in keeping them in check. The importance of this 

 theory, in* its bearing on the subject under discussion, rests on the 

 assumption of the predatory habits of the ants. From our own obser- 

 vations we are not inclined to attach much importance to the work of 

 ants, for the reason that frequent and close observations of these 

 insects in cotton fields and elsewhere have failed to verify previous 

 statements of their habit of voluntarily pre3dn^ upon bollworm larvae. 

 Under certain conditions, as when provoked, several species of ants 

 have been observed to attack and kill small bollworms, but the few 

 instances when ants have been observed feeding on larvae in the fields 

 have not been free from the suspicion that the worms had been pre- 

 viously injured and more or less disabled, as b}^ one of their fellows. 

 At no time during the past two years have any of the native cotton- 

 field ants been observed, under natural conditions, to voluntarily 

 attack bollworms. 



It remains to mention a fact doubtless of considerable importance, 

 namely, that rains produce in the cotton plant a rapid and more succu- 

 lent growth, which, by furnishing the larvae an abundance of tender 

 food, greatly favors their development. This and the increased food 

 supply for the moths under these conditions, as well as the increased 

 percentage which are able to escape from the soil, are reasons which in 

 themselves are almost sufficient to account for the greater destructive- 

 ness. An illustration of this is to be seen almost every year in the 

 known greater destructiveness of bollworms on "bottom-land" cotton 

 where the soil is moist and more fertile and the weed growth stronger, 

 as compared with the injur}?^ on the more stunted growth on uplands. 

 It is probable that the moths are primarily attracted to the ranker cot- 

 ton by reason of the greater nectar supply, and eggs are deposited on 

 these plants during the course of their feeding. 



The influence of shade, as during cloud}^ and rainy weather or by 

 reason of the luxuriant growth of cotton in closel}^ planted rows, is 

 also apparently favorable to the larvae, but it is to be noted that these 

 feed readily without seeming discomfort on the exposed portions of 

 the plants, often in the direct rays of the sun. 



In the egg stage the bollworm is subject to parasitism by a minute 

 chalcidid flv {Trichogrcmiwa pretiosa Riley), the importance of which 

 in destro3^ing bollworm eggs doubtless varies much with the character 



ffOomstock's Kept, on Cotton Insects, Washington (1879)', p. 378. 



