Effects of host larval stage preferences and diet on life history traits of Diadegma mollipla, an African parasitoid of the Diamondback Moth

Knowledge of the biological attributes of parasitoids plays a fundamental role in improved management of their pest hosts. Diadegma mollipla is a major indigenous parasitoid of the Diamondback Moth (DBM), Plutella xylostella (Linnaeus), in Eastern Africa. Two laboratory experiments were conducted to determine the DBM larval stage preferences of D.mollipla and their influence on life history traits and the effect of different diets (20% honey, 20% sugar solution, water or nothing) on adult parasitoid longevity. In the first study, 60 DBM larvae (15 each of larval stages L1-L4) were exposed to either one adult parasitoid female or four competing females in choice experiments. When DBM larvae were exposed to one parasitoid, in terms of parasitism, L1 and L2 were found to be the most preferred stages, followed by L3 and then L4. Sex ratio (females/males) increased with host larval stage from 1.3 to 3.1. Pre-imaginal development time was longer in L1 than in the other three stages. When exposed to four parasitoids, no significant differences in parasitism rates and progeny production were obtained between DBM larval stages. However, sex ratio increased from 0.8 in L1 to 4.1 in L4. Developmental time was longest in L4, intermediate in L1 and L3, and shortest in L2. In the diet experiment, honey and sugar were found to significantly increase longevity for D.mollipla adults of both sexes. Overall, combined adult male and female longevity was 24.5, 9.9, 2.2 and 1.9 days when fed on honey, sugar, water or nothing, respectively.