Laboratory test on secondary killing effect of hydramethylnon by coprophagous uptake of Blattella germanica

Abstract

As it was reported that hydramethylnon was excreted in the feces of bait-fed German cockroaches before being killed and coprophagous uptake by other cockroaches resulted in high mortality, we observed how long such a secondary killing effect lasts and how effectively kill them in the laboratory condition. A group of 30 1st instar nymphs was exposed to the feces excreted by 25 male bait-fed cockroaches for 10 days and the mortality rate was counted, and new group was re-introduced with 10 days intervals until the mortality dropped to the control level. The mortality rate was 81.1% in average of 1st-5th tests, 61.5% in 6th-14th tests and 15.2% in 15th-18th tests, showing 57.6% (943 dead/1,636 exposed) of the cumulative mortality rate during 180 days of the study period. When 25 4th-5th instar nymphs were exposed to hydramethylnon instead of 25 males, the mortality rate was 79.5%, 37.8%, 17.9% in average of 1st-6th tests, 7th-13th tests and 14th-17th tests, respectively, showing 48.9% (799 dead/1,635 exposed) of the cumulative rate during 180 days of the study period.