ACQUISITION and TRANSFER of a LAMBDA-CYHALOTHRIN MICROCAPSULE FORMULATION by BLATTELLA GERMANICA

Abstract:
The processes by which insects acquire toxic doses of the microencapsulated formulation of lambda-cyhalothrin (Demand CS) were studied using the German cockroach, Blattella germanica (L.). Cockroaches exposed to treated substrates acquired toxic doses of the insecticide rapidly, and HPLC analysis of cuticular washes of B. germanica established a linear relationship between exposure time and dose acquired during exposures of up to 4 minutes. These tests also showed that the pick-up process was highly efficient, with 3 times the LC dose acquired by cockroaches during <1 second contact with a treated 90 unglazed tile. The mechanical attachment of capsules to insects was weaker than expected, at least for a proportion of capsules. Treated cockroaches exposed to untreated surfaces lost capsules, although the relationship between loss of insecticide and time was not strongly linear. The weak attachment of capsules proved advantageous and accounted for the observed transfer of lethal doses between insects exposed to a residual application of lambda-cyhalothrin and unexposed insects. The transfer of insecticide to untreated cockroaches was shown to occur as a result of direct physical contact and not from secondary pick-up of capsules lost to surfaces from contaminated insects. The effect of insecticide transfer on expellency was determined using computer-aided techniques. No immediate flushing effect was recorded when cockroaches contaminated with lambda-cyhalothrin were introduced into an arena containing a harbourage with untreated cockroaches within. However, there was an overall excitatory effect over several hours following the introduction of the treated cockroach and during this period transfer of lethal doses of lambda-cyhalothrin occurred.