SECONDARY TRANSFER OF TOXICITY FOLLOWING CONSUMPTION OF FIPRONIL GEL BAIT BY ORIENTAL COCKROACHES (DICTYOPTERA: BLATTIDAE)

Abstract:
Necrophagy was shown to provide efficient transfer of fipronil toxicity from poisoned oriental cockroach (Blatta orientalis(L.)) cadavers to groups of untreated cockroaches in laboratory experiments. Adult females poisoned with Goliath gel deposits of 0.1 - 40 mg 0.05% w/w a.i. formulation were individually caged with 5 adult females following death. Mortality in the secondary populations increased with increasing weight of gel consumed by the primary cockroach and reached a higher level over 5 days when no alternative food was provided than when alternative food was available. Third instar nymphs (10) or adult females (5) were caged for 5 days in the jars in which adult females had consumed gel bait, died, and been removed. Mortality in the secondary populations again increased with weight of bait consumed by the cockroach. Under laboratory conditions, adult oriental cockroaches consumed 24.6 +0.9 and 24.7 +15.3 mg gel bait respectively within a 1 h period. The 5 day LD50 and LD95 of the gel bait for adult females were estimated to be 0.12 mg and 0.21 mg, respectively. A field trial was carried out in which two treatments of gel bait were applied with a 14 day interval to control oriental cockroaches. One area of the site was treated with gel deposits dispensed onto card squares (30 mg/deposit and 2.9 deposits/m2) which were removed after 48 h. 31% of these deposits were consumed within 48 h, with 100% consumed in or near harbourages. Females killed by freezing were placed in the monitored area following removal of the gel deposits, and 11% of these cadavers showed signs of necrophagy during the subsequent 3 days. The baiting operation reduced 5-day sticky trap catches to 16% of the pre-application catch by 14 days and to 1.4% of the pre-application catch by 30 days after the first treatment. Females caged with cadavers freshly recovered from the trial site after the first treatment were all killed within 48 h.