The biology of Encarsia tricolor: an autoparasitoid of whitefly

Encarsia tricolor Forster (Hym.: Aphelinidae) is an autoparasitoid of a number of whitefly pest species. Females develop as primary endoparasitoids, whereas males develop hyperparasitically in other whitefly endoparasitoids including conspecific females. Under a constant regime of 25 degrees C and 16:8 h L:D, the biology of E. tricolor was investigated using the Cabbage whitefly, Aleyrodes proletella, as host. The following results were obtained. (1) A significant positive linear correlation was detected between size and longevity for both sexes, given a honey diet. Mean (+/-SE) longevity was 16.9 +/- 0.62 days for females and 13.8 +/- 0.66 days for males. Females were significantly larger than males. (2) Female E. tricolor could develop in all host instars. Development times were slowest in first instar nymphs (22.3 +/- 0.34 days) and fastest in fourth instar nymphs (18.7 +/- 0.26 days). Female development times were not overtly variable. (3) Male E. tricolor could hyperparasitize all stages of conspecific female larvae and pupae offered. When parasitizing larvae, male development times were longer, indicating that male development is delayed until the host approaches pupation. (4) Mean (+/-SE) lifetime fecundity of E. tricolor laying female eggs was 85.36 +/- 13.85 at a mean rate of 7.31 +/- 0.27 eggs/female/day. (5) In a study of sex ratio dynamics in the parasitoid culture, emergent sex ratios were a function of the period of parasitism. The emergent sex ratio (percentage male) from individual leaves increased from 44% after 2 weeks in the culture to 76% after 4 weeks. A concurrent increase in the overall percentage parasitism was also recorded: 23 +/- 3.4% at 2 weeks to 87 +/- 4.1% at 4 weeks. (6) Observations on oviposition behavior indicated a clear preference to exploit late instar nymphs for female production. All whitefly instars were used for host feeding. Oviposition times for male eggs (in conspecific pupae) were significantly greater than for female eggs (in late instar whitefly nymphs).