Effects of host stages and temperature on population parameters of Oomyzussokolowskii, a larval-pupal parasitoid of Plutella xylostella

Oomyzus sokolowskii is a larval-pupal parasitoid of diamondback moth, Plute lla xylostella. In a host stage preference test, the parasitoid parasitised all larval and pupal stages, but exhibited a strong preference for larvae over prepupae or pupae, and did not show a preference among the larval inst ars. At 25 degrees C, the developmental time, number and sex ratio of offsp ring per host pupa, and successful parasitism did not differ significantly among parasitoids reared from host larvae of different instars, indicating similar host suitability between larvae of different instars. Mean developm ental times from egg to adult at 20, 22.5, 25, 30, 32.5, and 35 degrees C w ere 26.5, 21.0, 16.0, 12.7, 11.9 and 13.4 days, respectively. The favourabl e temperature range for development, survival, and reproduction of the para sitoid was 20-30 degrees C. However, wasps that developed and emerged at a favourable temperature could parasitise effectively at 32-35 degrees C for 24 hours. Life-fertility table studies at 20, 25, and 30 degrees C showed t hat each female wasp on average parasitised 3.1, 13.2, 6.8 larvae of diamon dback moth and produced 20.5, 92.1, 50.4 offspring, respectively, during he r lifetime. The highest intrinsic rate of natural increase (r(m)) of 0.263 female/day was reached at 30 degrees C as a result of the short mean genera tion time at this temperature compared to that at 20 and 25 degrees C, sugg esting that the parasitoid had the highest potential for population growth at relatively high temperatures.