Foraging egg parasitoids, Trissolcus vassilievi (Hymenoptera: Platygastridae), respond to host density and conspecific competitors in a patchy laboratory environment.

The egg parasitoid Trissolcus vassilievi (Mayr) is a key natural enemy of sunn pest, Eurygaster integriceps Puton (Hemiptera: Scutelleridae). This laboratory study examined how the aggregation of parasitoids varied in response to host density and numbers of foraging conspecifics. Five host densities (1, 2, 4, 8, and 15 clutches of E. integriceps eggs), were offered simultaneously to 1, 2, 4, 8, or 16 female wasps in a standardized arena (30 cm diameter) and patch residence times were recorded. Patch residence time was strongly correlated with parasitism, and increased as the number of host clutches increased up to eight, but declined when more clutches were offered. Wasps displayed low mobility and tended to remain in the patch initially encountered, even when it contained few egg masses. At higher wasp densities, patches were occupied more quickly, host exploitation began sooner, and per capita handling time was reduced. However, total patch residence times were similar across all densities. Thus, females responded to conspecifics with increased movement, which increased dispersal and resulted in a more homogeneous distribution of wasps among patches. Pseudo-interference, resulting from wasps remaining in some patches and neglecting others, had greater impact on final levels of host exploitation than did actual interference (patch abandonment following conspecific encounters). These phenomena resulted in decreased parasitoid searching rates and a 2-fold increase in host survival at higher wasp densities.

Susceptibility of Seven Selected Tomato Cultivars to Tuta absoluta (Lepidoptera: Gelechiidae): Implications for Its Management.

Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) is a serious pest originating from South America that affects tomato production in many countries, particularly in Iran (since 2010). In this study, by using age-stage, two-sex life-table parameters, the resistance of seven tomato cultivars, namely, 'Primo Early', 'Rio Grande', 'Cal JN3', 'Petomech', 'Early Urbana Y', 'Super 2270', and 'Super Strain B' to T. absoluta, was evaluated under laboratory conditions (25 ± 1 °C, 60 ± 5% RH, and a photoperiod of 16:8 (L:D) h). Larval and pupal periods were longest on Early Urbana Y, 13.86 and 6.52 d, respectively, and shortest on Cal JN3, 10.92 and 5.5 d, respectively. The longest and shortest development times of immature stages lasted 26.42 and 20.83 d on Early Urbana Y and Cal JN3, respectively. Male and female adult longevity was longest on Early Urbana Y, 30.42 and 38.52 d, respectively, and shortest on Cal JN3, 11.67 and 18.8 d, respectively. The net reproductive rate (R0) ranged between 80.94 (Cal JN3) and 45.87 (Primo Early) offspring. The lowest and the highest values of the intrinsic rate of increase (r) and finite rate of increase (λ) were on Early Urbana Y and Cal JN3, 0.1052 and 0.1522 and 1.1109 and 1.1644 d-1, respectively. The mean generation time (T) on different cultivars varied from 30.47 to 37.28 d. Our results indicated that Cal JN3 was the most susceptible to infestation and Primo Early and Early Urbana Y were the most resistant to T. absoluta among the tomato cultivars tested.