Manner of Pickup of VLV Malathion by Grasshoppers from Aerially Sprayed Rangeland1

Abstract

Experimental control of an infestation of range grasshoppers with 8 fl oz ULV malathion applied by aircraft was carried out to study the pickup of the toxicant by 3 species, Ageneotettix deorum (Scudder), Amphitornus coloradus (Thomas), and Aulocara elliotti (Thomas). Caged grasshoppers were subjected to 5 treatments: (1) sprayed food and soil plus exposure to spray at time of application, (2) sprayed food, (3) exposure to spray at time of application, (4) sprayed soil, and (5) check untreated. A deorum and A. elliotti reacted similarly to the treatments, but A. coloradus exhibited interesting variations. Among caged individuals of A. deorum, treatments 1 and 2 resulted in mortality of 98 and 96%, respectively. 6.5 days after start of the tests; among caged individuals of A. elliotti both of these treatments caused 98% mortality; treatment 3 caused 22% mortality of A. deorum and 15% mortality of A. elliotti; treatment 4 did not differ significantly from the check. Mortality of A. coloradus was 98% in treatment 1 and 89% in treatment 2; no difference in mortality from the check occurred in treatments 3 and 4. The difference in response to treatment 3 by A. coloradus was attributed to difference in behavior; this species rests deep in grass which protects the grasshoppers from falling droplets of insecticide, whereas the other 2 species rest on bare ground. It was concluded that deposits of insecticide on vegetation were the source of most mortality and that the grasshoppers probably ingested the toxicant with their food.