Intraspecific interference between native parasitoids modified by a non‐native parasitoid and its consequence on population dynamics

Abstract

1. The number of natural enemies that should be introduced to control a pest is a controversial subject in biocontrol. A previous semi-mechanistic model parameterised using a laboratory system consisting of two parasitoid wasps, Anisopteromalus calandrae and Heterospilus prosopidis, parasitising a pest beetle, Callosobruchus chinensis, indicated that the introduction of the non-native parasitoid H. prosopidis decreases the level of intraspecific interference between native A. calandrae females. The model also suggested that this decrease was the main factor destabilising the population dynamics of the host-parasitoid system, resulting in chaos. 2. To test this population-level decrease and host density independence in the interference of A. calandrae, we observed individual behaviours to quantify the level of intraspecific interference between two A. calandrae females in the presence or absence of H. prosopidis at two different host densities. 3. When H. prosopidis was present, the number of direct antagonistic interference events between A. calandrae females, sting duration, host feeding events (but not stinging events), and patch residence time were reduced. However, the presence of H. prosopidis decreased the patch residence time and the proportion of hosts parasitised by A. calandrae only when the host density was low. 4. The reduction in intraspecific interference between A. calandrae females by H. prosopidis and its host density independence support the population-level prediction, whereas the observed reduction in host-feeding behaviours in A. calandrae by H. prosopidis was not predicted. Overall pest control by the native parasitoid was unaffected by the non-native parasitoid as host density increased.

Optimal rearing medium for the population growth of the predatory mite, Amblyseius swirskii (Athias-Henriot) (Acari: Phytoseiidae)

“…Because moisture increased in the SY diet after 2 weeks, this may have disturbed the foraging and reproduction of A. swirskii (even though C. lactis was still able to reproduce in these conditions). High prey densities might interfere with A. swirskii on the SY diet (Chant 1961); additionally, a saturating type II functional response as well as mutual interference by A. swirskii itself (Fathipour et al 2020) may limit oviposition rates and fecundity (Nakamichi et al 2020). In this study, A. swirskii populations (both males and females) increased 40.5 times after 30 days without additional prey at an initial predator:prey ratio of 1:20, on the baker's yeast diet.…”

Low concentrations of selenium nanoparticles enhance the performance of a generalist parasitoid and its host, with no net effect on host suppression

“…Note that we refer to a 'replicate' as a repetition of the complete set of treatment combinations (eight SeNP concentrations × two sexes), and, to reiterate, the parasitoids (400 in total) were subjected to treatment combinations individually rather than as part of a group. Although toxicity testing on groups of organisms is both common and convenient (with replication at the level of each set of groups), that approach is problematic, especially for A. calandrae because female A. calandrae exhibit high levels of density-dependent intraspecific interference competition 35,48,49 ; if these parasitoids were exposed to SeNPs in a group, then the resulting differential rates of death across groups treated with different concentrations would introduce an increasing asymmetry in the behavioral interactions among the individuals in each group over time, which would be a confounding variable.…”