Bulletin of Insectology 62 (2): 221-228, 2009 ISSN 1721-8861 Development of a methodology to study the intrinsic rate of increase of whitefly parasitoids: design of an oviposition device Jean Claude ONILLON 1 , Pascal MAIGNET 2 , Giovanna TROPEA GARZIA 3 1 INRA, Station de Lutte Biologique, Valbonne, France 2 Biotop, Valbonne, France 3 Dipartimento di Scienze e Tecnologie Fitosanitarie, Università di Catania, Italy Abstract 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, lon- gevity 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 vaporari- orum (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 parasi- toids because it reduces variations of abiotic origin. Key words: Aleyrodidae, Aphelinidae, Trialeurodes vaporariorum, Encarsia formosa, adult, oviposition device, intrinsic rate of increase, fecundity, longevity, host-feeding. Introduction The traditional integrated control strategy on horticul- tural and ornamental protected crops, based mainly on the use of beneficial insects, has been changed greatly since the arrival of the biotype “B” of the whitefly Be- misia tabaci (Gennadius) (Homoptera Aleyrodidae) in the western part of the Mediterranean basin. Before its introduction, the only injurious whitefly was Trialeu- rodes vaporariorum (Westwood) (Homoptera Aleyrodi- dae) which can be successfully controlled by the parasi- toid Encarsia formosa Gahan (Hymenoptera Aphelini- dae). Only a few studies pointing out the specific bio- logical features of this parasitoid, such as the major ef- fect of temperature, have been carried out under ex- perimental conditions (Burnett, 1949; Kajita, 1979; Arakawa, 1982). This feature varies according to the population structure of the pest [single nymphal instar (Burnett, 1949; Arakawa, 1982); many nymphal instars (Kajita, 1979)] and with or without feeding on honey- dew (Vet and van Lenteren, 1981). The first change in research orientation occurred with the rise in greenhouse-heating costs. The progressive cost reduction of inputs favoured research oriented to- wards a better knowledge of intrinsic-rate-of-increase parameters of E. formosa under constant low tempera- tures (van Lenteren and Schaal, 1981), and towards the use of less exigent species such as Encarsia tricolor Förster (Hymenoptera Aphelinidae) (Christochowitz et al., 1981). Nevertheless, the large heterogeneity of re- sults obtained as a consequence of the variety of adopted protocols did not lead to a reliable standard methodology for estimating biotic-parameters of a para- sitoid species under different abiotic factors. In addition, the results obtained did not provide a valid comparison for the performance of the various beneficial insects to be released. The introduction of the biotype “B” of B. tabaci and trials of indigenous parasitoids or of exotic beneficial insects justify the use of a methodology allowing the re- liable comparison between intrinsic rate of increases of these indigenous and exotic insects or between stocks of the same insect. Starting from 1995 (Brown et al., 1995), several systematic studies characterize the biotypes of B. tabaci living in the Mediterranean basin (Guirao et al., 1996; 1997a; 1997b; Chermiti et al., 1997; De Barro et al., 2000; Simón et al., 2003; Bosco et al., 2006; De La Rùa et al., 2006) and checklists of their parasitoids are published for the Mediterranean basin and for other re- gions of the world (Polaszek et al., 1992; Onillon et al., 1994; Riley and Ciomperlink, 1997; Stansly et al., 1997; Schuster et al., 1998; Benral Vega, 2000a; 2000b; Smith et al., 2000; Viscaret et al., 2000; Lopez-Avila et al., 2001). These checklists revealed a rich and diversified parasitic entomofauna which needs to be carefully char- acterized in order to estimate their efficacy and to com- pare their performance. It mainly concerns of Encarsia pergandiella Howard, Encarsia hispida De Santis, En- carsia inaron (Walker), Encarsia sophia (Giraud et Dodd) and Eretmocerus mundus Mercet.