Mate‐guarding behaviour is regarded as a means of increasing paternity share by reducing sperm competition. It is known to be a plastic response which varies with operational sex ratios and competitor presence in the vicinity. In a recent study, prolonged mating duration in Menochilus sexmaculatus (Fabricius) (Coleoptera: Coccinellidae) has been found to incorporate mate‐guarding behaviour. The present investigation was conducted to assess its plasticity in the presence of competitors. The physical and chemical presence of competitors of both sexes at varying densities was provided to a pair of ladybirds, and their time to commence mating, latent period and mate‐guarding duration was observed. These were compared to a control treatment where other partners were absent. All treatments were conducted with sibling as well as non‐sibling competitors. It was our hypothesis that mate guarding would be increased in the presence of male competitors and would be reduced by female presence. The results revealed that while mate‐guarding duration was increased by the chemical presence of males it was decreased by their physical presence. The latter result was attributed to interference by other males who dislodge the mating male in order to access the female. Female chemical presence had no effect on mate guarding, while physical presence increased the duration of mate guarding. The reasons for the latter behaviour require further investigation. Responses were not significantly affected by the relationship between the focal pair and the competitor. The authenticity of the mate guarding in this ladybird is strongly affirmed by our results.
Under natural conditions, prey resources may fluctuate considerably in space and time; and predators are continuously faced with challenges of resource availability and use. In this study, effects of fluctuations (scarce/optimal/abundant) in biomass of pea aphid (Acyrthosiphon pisum (Harris); Hemiptera: Aphididae) during rearing and experimental conditions on certain predatory attributes (consumption rate/conversion, efficiency/growth rate) of two sympatric aphidophagous Coccinellidae (Coleoptera) were evaluated. Results revealed significant influence of rearing conditions on conversion efficiency and growth rate; and experimental conditions on all three predation attributes of Menochilus sexmaculatus (Fabricius) (Coleoptera: Coccinellidae). Larvae/adults of M. sexmaculatus had similar consumption rates per rearing condition, but exhibited highest and lowest consumption rates when abruptly shifted to abundant and scarce prey experimental conditions. Further, scarce prey reared larvae/adults of M. sexmaculatus displayed highest conversion efficiency and growth rate on optimal/abundant prey experimental condition(s). However, all three predation attributes of larvae/adults of Propylea dissecta (Mulsant) (Coleoptera: Coccinellidae) were influenced substantially by both the rearing and experimental conditions; and scarce prey reared larvae/adults exhibited highest predation attributes on optimal/abundant prey experimental condition(s). Moreover, predation attributes of M. sexmaculatus were higher than P. dissecta on the three experimental conditions. Therefore, this study suggests that M. sexmaculatus has a better compensatory ability to overcome prey resource fluctuation than P. dissecta.
In the present study, resource partitioning by natural conspecific size variants (small and large) of ladybird, Menochilus sexmaculatus (Fabricius) females, in response to varying prey densities was assessed using functional and numerical responses as measures of prey density. The prey provided was small (second) and large (fourth) instars of Aphis craccivora Koch. Results revealed that under choice condition, small and large females of M. sexmaculatus consumed higher number of small and large instars, respectively. Small females exhibited a modified Type II functional response on small aphid instars and a Type II functional response on fourth aphid instars. Large females exhibited a Type II functional response when provided either second or fourth aphid instars. Numerical response in terms of numbers of eggs laid by both the females increased with increase in the density of either of the aphid instars. However, in small females, oviposition had a positive correlation with the numbers of small and large aphid instars consumed; being strong for the small aphid instars. While in large females, oviposition was positively correlated with the numbers of large aphid instars consumed and not small aphid instars. It therefore seems that intraspecific resource partitioning in M. sexmaculatus occurs prominently in large females than the small females.
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