Influence of repellency on the efficacy of blatticides. II. Laboratory experiments with German cockroaches.

Abstract

The efficacy of insecticides under simulated field conditions in which German cockroaches, Blattella germanica (L.), had the opportunity to avoid the insecticide deposits (choice boxes or mock-up wall voids) was approximately inversely proportional to their contact activity when the insects were continuously confined with the deposits (petri-dish tests). The addition of attractants to insecticides or to areas in which they were applied did not appreciably counteract their repellency, which was the principal factor affecting their efficacy. An 8-fold increase in the quantity of insecticide dust of a given concentration of toxicant, when applied to the dark compartment of a choice box, generally did not significantly increase the kill of German cockroaches, but doubling the concentration of toxicant greatly increased it. Simulated field treatment against German cockroaches was adversely affected by physiological resistance or reduced concentration of toxicant, but only because the insects could take advantage of the slower insecticidal activity to begin evasive action before their initial exploratory Contacts with the toxicant became fatal. When deposits of boric acid formulations in open petri dishes were exposed to air of moderate humidity for 3 months, their insecticidal efficacy did not decrease, but when they remained in water-saturated air for 3 months and were then dried, the powders were not so fluffy and were not picked up as readily by the cockroaches. The addition of certain adjuvants had the effect of preventing agglomeration of boric acid particles and decreasing the adverse effects of prolonged high humidity. Storage of boric acid formulations in moisture-proof containers is recommended. In treated choice boxes and mock-up closets the rate of cockroach mortality increased with increased light intensity, since the area of acceptable insecticide-free harborage was decreased by the light. Increased environmental complexity decreased the effect of light on mortality. In an untreated choice box or closet, the closer the food and water were placed to the preferred harborage sites, the lower the rate of mortality. Cockroaches having approximately a 1-second contact with dust deposits carried away with them a lethal dose of insecticide, whereas a 5-minute contact with deposits from dilute solutions of insecticides that kill by cholinesterase inhibition did not result in the death of the insects in 48 hours. Organochlorine insecticides had a more potent latent effect than organophosphorus and carbamate insecticides. In wall-void tests, the efficacy of 5 insecticide dusts 30 days after treatment was in the order boric acid>2% diazinon>Drione = sodium fluoride>2% Baygon. Deposits from an aqueous solution of boric acid + detergent gave a 50% kill of cockroaches continuously confined to them in approximately 6 days on asphalt, red-clay tile, or glass, and 12.3 days on concrete. They gave a 63.5% net kill in 2 weeks in a mock-up kitchen. the floor of which was mopped once with the solution.