COMPARATIVE TOXICOLOGY OF LIPOSCELIS ENTOMOPHILA AND L. BOSTRYCHOPHILA IN RELATION TO THEIR MANAGEMENT

Abstract

The life history of Liposcelis entomophila was investigated at 30 ± 1°C and 75 ± 3% r.h. A culturing regime to obtain populations of 1-3 week old female liposcelids was established.

The use of CO 2 was explored as a residue-free alternative in the control of liposcelids. L. bostrvchophila was found to be the more tolerant of the two species to CO 2 treatment. The most tolerant life stage for both species are the eggs. At 45% and 60% CO2, increases in exposure periods resulted in corresponding increases in mortality in both species. However, no decrease in either LT50 or LT95 values was observed with an increase in CO 2 concentration from 45% to 60%. Examination of liposcelid responses to fixed exposure periods showed that above 45% CO,, no corresponding increases in mortality were observed in either species at sublethal dosages.

L. entomophila was the more tolerant of the two species to the five organophoshorus and two carbamate insecticides tested, with malathion being least effective against both species. Chlorpyrifos-methyl was found to be the most effective insecticide against L. bostrychophila.

Esterases from L. bostrychophila had a significantly higher specific activity towards ?-naphthyl acetate than those from L. entomophila. Of the various inhibitors tested, dichlorovos was found to be the most potent whilst the carbamate inhibitors proved least effective in both species. Esterases from L. entomophila were least effective in both species. Esterases from L. entomophila were less susceptible to inhibition than those from L. bostrychopila implicating the involvement of esterases in the resulting higher tolerance of L. bostrychophila to various organophosphorus and carbamate insecticides. Based on the selective inhibition on polyacrylamide gels, eleven B-esterases, two A-type-esterases and one acetylcholinesterase were detected in L. entomophila whilst the corresponding numbers in L. bostrychophila were 9, 1 and 1.

The Ki values for inhibition indicated that acetylcholinesterase sensitivity was not responsible for the differences in the susceptibility between the two species nor amongst the insecticides for each species.

An integrated management programme for liposcelids is discussed in the light of these findings.