Relationships between Body Size and Parasitic Fitness and Offspring Performance of Sclerodermus pupariae Yang et Yao (Hymenoptera: Bethylidae)

Abstract

The relationship between body size and fitness in parasitoid wasps has several effects on parasitic ability, reproductive behavior in female wasps, and progeny fitness. Female wasps with various body sizes were obtained by mass-rearing a gregarious ectoparasitoid, Sclerodermus pupariae, which is one of the excellent parasites to control the larvae and pupae of Buprestidae and Cerambycidae. We investigated the effects of body size of adult females introduced on Thyestilla gebleri (Coleoptera: Cerambycidae) larvae on their paralysis time, pre-oviposition period, oviposition period and fecundity, and the related fitness of their offspring. Results showed that small female wasps needed more time to paralyze a host and had a higher mortality rate than large female wasps. More offspring were produced by large female wasps than by small female wasps, and the percentage and body size of female offspring was not affected by maternal body size. The duration of the egg stage was not affected by foundress size, nor was that of the pupal stage, but the duration of the larval stage and generation time of small female wasps was longer than that of large females. Our findings suggest that the parasitic fitness and offspring performance are affected by maternal size, and there is need to choose reasonable body size of female wasps, to optimally utilize mass rearing and to control target pests with the lowest mortality cost.

Fig 1. The reproduction time of Sclerodermus pupariae with various body sizes.

(a) paralysis time (Chi–square = 9.424, df = 2, P = 0.009), (b) pre–oviposition period (Chi–square = 4.75, df = 2, P = 0.093), and (c) oviposition period (Chi–square = 2.258, df = 2, P = 0. 323) (Log–rank test).

Fig 2. Relationship between body size of female wasps and fecundity (number of offspring emerged).

Effect of body size on fecundity (number of offspring emerged) is significant (y = 25.434x – 21.136, R² = 0.1495, F = 13.53, df = 1, 77, P < 0.0001).

Fig 3. Offspring performance of Sclerodermus pupariae with mothers of various body sizes.

(a) numbers of female offspring (y = 16.394x – 0.7234, R² = 0.0581, F = 4.75, df = 1, 76, P = 0.032), (b) sex ratio (proportion of females) (F = 2.03, df = 2, 75, P = 0.14), (c) body size of female offspring (y = –0.0024x + 2.8051, R² = 8 × 10⁻⁵, F = 0.006, df = 1, 76, P = 0.94). Bars indicate standard errors and different letters indicate significant differences at P ≤ 0.05 with Tukey’s multiple comparison (ANOVA).