Threshold temperature for development of a North American diamondback moth population and its larval parasitoid, Diadegma insulare

The present lower threshold temperature for the world`s most destructive insect pest of cruciferous crops diamondback moth (DBM), Plutella xylostella (Lepidoptera: Plutellidae), is 7.3°C, but there is no upper threshold temperature for DBM.  Neither there is a set threshold temperature for DBM’s major natural enemy, Diadegma insulare (Hymenoptera: Ichneumonidae).  We conducted a laboratory study to determine the survival and development of a North American DBM population and its larval parasitoid D. insulare at twenty constant temperatures ranging from 2 to 38°C.  Data were then fitted to one linear and two nonlinear models. Considering as criteria the goodness of fit and the ability to estimate parameters of biological significance, the Wang Model was the most adequate to describe the relationship between temperature and development of both species.  The development of DBM from second larval instar to adult was successfully completed at temperatures as low as 4°C and as high as 37°C.  The temperature range for completing the life cycle from egg to adult of D. insulare was from 5 to 32°C. This suggests that temperature in North America is not a limiting factor for either DBM or its larval parasitoid D. insulare.