Diadegma mollipla parasitizing Plutella xylostella: host instar preference and suitability

Abstract

Oviposition decisions (i.e., host selection and sex allocation) of female parasitoids are expected to correspond with host quality, as their offspring fitness is dependent on the amount and quality of resources provided by a single host. The host size model assumes that host quality is a linear function of host size, with larger hosts believed to contain a greater quantity of resources, and thus be more profitable than smaller hosts. We tested this assertion in the laboratory on a solitary larval-pupal parasitoid Diadegma mollipla (Holmgren) (Hymenoptera: Ichneumonidae) developing on three instars (second-fourth) of one of its hosts, the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae). In a no-choice test, parasitism levels and sex ratio (i.e., proportion of female progeny) were significantly high in hosts attacked in the second instar followed by third then fourth instars. However, the few parasitoids that completed a generation from the fourth instars did so significantly faster than conspecifics that started development in the other two instars. In direct observations, however, the parasitoids (i) randomly attacked the various host instars, (ii) spent a similar period examining the various host instars with their ovipositors, (iii) subdued all three host instars with about the same effort, and (iv) no statistical differences were observed in the attack rates on the three host instars. In a choice test, the females parasitized significantly more third instars followed by second then fourth instars. However, total parasitism in this experiment was 43% lower compared to parasitism of only second instars in the no-choice test. No significant differences were detected in progeny sex ratios. In both choice and no-choice tests, significantly more fourth instars died during the course of the experiments than second instars, while third instars were intermediate. The higher parasitism of third than second instars in the choice test indicates that the females perceived larger hosts as higher quality than smaller hosts, despite their lower suitability for larval development.

Host Suitability of a Gregarious Parasitoid on Beetle Hosts: Flexibility between Fitness of Adult and Offspring

“…Both theories stress that there were trade-offs between maternal fitness through host-feeding [27]–[28] and enhanced reproduction through oviposition on the same host individual as used for host-feeding [9], [29]. However, we found that optimum foraging strategy was combined with optimum oviposition strategy.…”

Effects of Host Age on the Parasitism ofPachycrepoideus vindemmiae(Hymenoptera: Pteromalidae), an Ectoparasitic Pupal Parasitoid ofBactrocera cucurbitae(Diptera: Tephritidae)

“…We speculate that 3 or 4-day old pupae may provide better nutritional quality than pupae of other ages. Other parasitoid species, i.e., Diadromus collaris (Wang & Liu 2002), Diadegma mollipla (Nofemela 2008) and Microplitis mediator (Li et al 2006), also showed a preference for hosts of a particular age.…”

First report of Trichospilus diatraeae (Hymenoptera: Eulophidae) parasitizing pupae of Methona themisto (Lepidoptera: Nymphalidae)

“…Pupae that did not suffer parasitism were those that had the lowest weight. Parasitoid females look for the largest possible host, as it will possibly have the greatest quantity and quality of food resources for their offspring (Lin and Alves, 2003;Nofemela and Kfir, 2008). Non-parasitism of pupae 5 and 6 may be linked to the quality of the host.…”