Do resource value and ownership status affect intensity and resolution of contests in a parasitoid wasp?

Abstract

International audienceBiological control of bruchid beetles, Callosobruchus maculatus (Fabricius) (Coleoptera: Bruchidae), infesting cowpea seeds, Vigna unguiculata (L.)Walpers (Fabaceae), can be performed via augmentative releases of Dinarmus basalis Rondani (Hymenoptera: Pteromalidae) parasitoid wasps. Females of the latter species are therefore likely to experience intense intraspecific competition: they should encounter numerous previously parasitized hosts but also conspecific competitors, with which they may fight to secure hosts on which to lay their eggs. Such contests might therefore disrupt biological control programs. Here, we studied aggressive behavior that D. basalis females show toward conspecific competitors and subsequent host exploitation strategies. We further investigated factors that classically affect contest intensity and outcomes in animals, such as the effect of ownership status, by manipulating the residency period before the intruder's arrival. In addition, we tested the effect of the size of female reproductive tissue (measured in terms of egg load) and the quality of the habitat previously experienced by females (either rich or poor in hosts). These two factors are expected to influence the value that females place on the host and therefore the costs they are willing to pay to win it. Finally, we discussed the consequences of agonistic behaviors on females' host exploitation strategies. Our results suggest that contest competition may actually enhance host control by favoring parasitoid dispersion, rather than disrupting it

Observations of parasitism and aggression by female Enoggera nassaui, an egg parasitoid of the eucalypt pest, Paropsis charybdis

“…The parasitism sequence for E. nassaui was similar to the behaviour of Pachycrepoideus vindemiae (Goubault et al 2007) and D. basalis (Mohamad et al 2013), except for the frequency of host feeding. For the pupal parasitoid P. vindemiae, host feeding takes place after several hosts have been attacked, increasing the number of eggs a female can mature and/or providing energy to search for hosts (Phillips 1993;Goubault et al 2007).…”

“…Again, this is similar to Pachycrepoideus vindemiae (Goubault et al 2007) and D. basalis (Mohamad et al 2013). Females (whether owners or intruders) that were interrupted during the parasitism sequence before completing oviposition would usually revert back to drumming (the beginning of the parasitism sequence) when they resumed parasitism after aggressive interactions finished.…”

“…Survival analysis followed by log-rank tests was used to compare time spent on parasitism-related behaviour between (1) solo and owner females and (2) solo and intruder females, following the approach of Mohamad et al (2013). Survival analysis was chosen to analyse the time data (behaviour durations related to oviposition events) because this type of analysis can handle unequal sample sizes, censored observations and data that are not normally distributed (Manly 1992).…”

“…This may explain why it was rare for host ownership to be resolved clearly even after frequent contests. A longer period between arrival of owner and intruder may be needed to confer a consistent advantage to E. nassaui owners (Field and Calbert 1999;Mohamad et al 2013).…”

“…If female-female aggression is common across Enoggera spp., there may be unexpected consequences for ongoing and future biological control programmes. Aggression between conspecifics increased the time needed to complete oviposition in another parasitoid, Dinarmus basalis Rondani (Hymenoptera: Pteromalidae), and it was hypothesised that contests between females would enhance biological control by encouraging parasitoid dispersal (Mohamad et al 2013). This parasitoid attacks a stored product pest where hosts will be aggregated within storage facilities, which is very different from the situation of E. nassaui females searching for a forestry pest within large-scale plantations.…”