Report 
  Title  
  TOXICITY OF HYDRAMETHYLNON TO BLATTA ORIENTALIS L. BY DIRECT AND INDIRECT EXPOSURE, AND EFFECTS OF HYDRAMETHYLNON BAITS AGAINST A MIXED POPULATION OF BLATTA ORIENTALIS L. AND BLATTELLA GERMANICA (L.) IN A SIMULATED DOMESTIC ENVIRONME
  Key Words  
  Transferred troxic effect, insecticide transfer, indirect exposure
  Author  
  J.E. SHORT, H.J. MOSSON, J.L. WORSLEY AND J.P. EDWARDS
  Abstract  
  Small groups of nymphs and adults, or of 5th and 6th instar nymphs of the Oriental cockroach Blatta orientalis, were exposed to hydramethylnon baits Maxforce) for periods of time ranging from 1 to 14 days. These insects were also given access to standard laboratory cockroach food as an alternative to the hydramethylnon baits. In these tests, hydramethylnon baits produced high mortality (>90%) when exposure to the baits was allowed for 3 days or longer. When exposure to hydramethylnon baits was limited only to 24 hr, mortality also reached high levels, although populations containing adults appeared to be rather less affected than populations comprising 5th and 6th instar nymphs only. In tests investigating the transfer of hydramethylnon from treated cockroaches to conspecifics, 5th and 6th instar nymphs that had been exposed to hydramethylnon baits for different periods of time, were transferred to a clean glass tank containing a second, similar group of cockroaches that had not previously been exposed to the baits. After transfer, all cockroaches were fed only on standard laboratory cockroach food. In these tests, the mortality of the cockroaches directly exposed to the baits was similar to that recorded in the previous test. However, after 28 days, there was a noticeable mortality (30-50%) in the insects that had not had any previous direct exposure to hydramethylnon bait, but did have contact with cockroaches that had been exposed previously to the bait for 3-7 days. After 10 weeks, mortality in some of these indirectly-exposed cockroaches reached 100%. This transferred toxic effect was found to be transmitted by contact with (or consumption of) hydramethylnon contaminated dead bodies, faeces and harbourages. Finally, a mixed, semi-natural infestation of B. orientalis and Blattella germanica was established in a simulated domestic environment, and exposed to hydramethylnon baits. During the first 12 weeks of this large-scale experiment, average Roatel trap counts (a standard method of population assessment) declined from a mean total of 504 insects to only 2 insects in the case of Blattella germanica, and from 208 insects to 33 insects in the case of B. orientalis.