The mortality of three species of Psocoptera, Liposcelis bostrychophila Badonnel, Liposcelis decolor Pearman and Liposcelis paeta Pearman, at moderately elevated temperatures

Psocids are becoming serious pests in storage structures and standard practices of protection and disinfestation frequently fail. One possible alternative is heat disinfestation at moderately elevated temperatures (approximate to 45-55degreesC). Heat has several advantages such as being pervasive, relatively rapid and residue free, but little is known about dosages for the removal of psocid infestations. Therefore, it was necessary to determine the heat tolerance of a range of species that might reasonably be expected to differ in heat tolerance. Liposcelis bostrychophila, Liposcelis decolor and Liposcelis paeta were investigated to determine the times required to achieve mortality in the most heat tolerant developmental stage. The psocids were exposed to a single step temperature/time dose, where the temperature experienced by the insects was continuously monitored and environmental moisture loss was minimised. The egg was generally found to be the most tolerant stage and a linear predictor model was used to determine a range of lethal treatment times (LTs) from LT 50 to LT 99.99 for the stage for each species. Logit, probit and complementary log-log links were investigated with the logit link giving the best fit for L. bostrychophila and the log-log link giving the best fit for the other two species. Comparing egg mortality, L. decolor was found to be the most heat tolerant at temperatures from 46degreesC to 51degreesC, while below 46degreesC, L. paeta became considerably more tolerant than the other two species. L. bostrychophila was generally more susceptible than L. decolor, although it was relatively less susceptible at lower temperatures as LT levels increased above LT 99. L. paeta was the most susceptible species at and above LT 99 from 47degreesC to 51degreesC. The psocids were considerably more vulnerable to heat disinfestation at moderate temperatures than either Rhyzopertha dominica or Sitophilus oryzae. (C) 2002 Elsevier Science Ltd. All rights reserved.