Temperature-dependent development of four egg parasitoid Trichogramma species (Hymenoptera: Trichogrammatidae)

Trichogramma species have been successfully utilized for biocontrol of several lepidopteran pests worldwide. The development, survival and progeny production of two Kenyan species' Trichogramma bournieri Pintureau & Babault and Trichogramma sp. nr. mwanzai Schulten & Feijen (collected from Kenya), Trichogramma evanescens Westwood (Germany) and Trichogramma chilonis Ishii (India) was studied at four constant temperatures (13, 18, 25 and 34degreesC) with the aim of assessing the relative biotic potential of the two native species for biocontrol of Helicoverpa armigera and Plutella xylostella in Kenya. The study was conducted at the Institute for Biological Control (BBA), Darmstadt, Germany. The Trichogramma species tested showed variations in fertility, developmental time, percent emergence, progeny production and sex ratio at the four temperature regimes. Fertility decreased as temperature increased from 25 to 34degreesC. T. chilonis and T. evanescens completed development at all temperatures tested, but T. bournieri and T. sp. nr. mwanzai failed to complete development at 13degreesC. The developmental period for all the species decreased as the temperature increased. The duration of development from oviposition to adult emergence varied from 8 days to 12 weeks shorter at 34degreesC than at 13degreesC for T. chilonis and T. evanescens. For the various temperatures tested, a linear model was satisfactory for egg to adult development at P = 0.05 for T chilonis and T. evanescens. The lower temperature thresholds for development and duration in degree-days were 8.83degreesC and 188 for T. chilonis and 9.23degreesC and 192 for T. evanescens, respectively. For all temperatures tested, T. sp. nr. mwanzai had the highest preimaginal survivorship. Adult emergence was lower at 13degreesC and 34degreesC than at 18 and 25degreesC The highest fertility (mean SE) (50.37 +/- 2.32 adult female(-1)) and progeny production (44.03 +/- 2.02 adult female(-1)) was recorded at 25degreesC for T. evanescens. Sex ratio was biased towards female at all temperatures in T. bournieri and T. chilonis. At all temperatures tested, T. sp. nr. mwanzai produced more males than females. For all species tested, favourable parasitism was between 18 and 25degreesC. The results from this study will be useful for mass rearing purposes as well as for future field release programmes.