Development of a methodology to study the intrinsic rate of increase of whitefly parasitoids: design of an oviposition device

The present work contributes to an accurate quantification method of the parameters of the biotic potential of Encarsia formosa Gahan (Hymenoptera Aphelinidae), applicable to other species of whitefly parasitoids. The oviposition devices are easy to make and they allow standardisation of a whitefly parasitoid study by daily observations of the main parameters such as fecundity, longevity and host-feeding by adult parasitoids, which are important for the parasitoids mass-production and biological control of whiteflies. Results show that two physical parameters determine the expression of biotic potential: the confinement induces an important decrease of the fecundity and longevity of E. formosa; the position of plant leaf with nymphs of Trialeurodes vaporariorum (Westwood) (Homoptera Aleyrodidae) that the parasitoid female can explore for oviposition and host-feeding influences on the biotic potential. The heterogeneity observed in the replicates suggests that during their mass-processing the parasitoids suffer abiotic conditions leading to changes in the biotic potential of progeny. Under strictly constant laboratory conditions of temperature, hygrometry and photoperiod, an identical trend is observed for mother and daughter generations: fecundity and longevity are higher in aired oviposition devices and exploitable host-nymphs on leaf situated on top of device. In these laboratory conditions, results for fecundity and longevity are better, and the same trend is observed for host-feeding of mother and daughter generations. The above defined standardised methodology will allow comparison of the biotic potential of other species of whitefly parasitoids because it reduces variations of abiotic origin.