Operational sex ratio and paternal age sway mating and reproductive performance inMenochilus sexmaculatus(Coleoptera: Coccinellidae)

Abstract

Operational sex ratio and paternal age are known to independently affect mating behaviour and reproductive performance. We conducted experiments to assess the effects of operational sex ratio and paternal age on mating, reproduction, and total development duration of Menochilus sexmaculatus (Fabricius) (Coleoptera: Coccinellidae). Three male-biased sex ratios, no (1:1), modest (1:2), and extreme (1:5) competition treatments, were formed using young, middle-aged, and old males. The reproductive performance of M. sexmaculatus at all ages under extreme competition (1:5) surpassed the other two treatments. More competition among males decreased the time of commencement of mating and increased the duration of copulation. Females laid a greater number of eggs in extreme competition treatments. The operational sex ratio (irrespective of age) had no significant effect on the total developmental duration of offspring. Among different age groups, older males took more time to commence mating and mated for longer durations in all the sex ratio treatments. The number of eggs in the first clutch was lowest when females were mated with older males with increased offspring development duration. Thus, it can be concluded that male-biased sex ratio elevates the performance of M. sexmaculatus. Among different age groups, older males were poor performers than young and middle-aged males.

Effects of Delayed Mating on the Reproductive Performance of Henosepilachna vigintioctopunctata (F.) (Coleoptera: Coccinellidae)

“…In other insects, when the hatch rates were shown to be affected as a result of delayed mating in females versus males, the results have varied widely depending on the species. For example, egg hatchability in A. orientalis was not affected by mating delay [35], while delaying mating in Cheilomenes sexmaculata [59], Dasylepida ishigakiensis [33], Zygogramma bicolorata [34], Menochilus sexmaculatus (Fabricius) (Coleoptera: Coccinellidae) [40], Coccinella septempunctata [61], Propylea dissecta (Mulsant) (Coleoptera: Coccinellidae) [77,78], and Callosobruchus maculatus (Fabricius) (Coleoptera: Bruchidae) [70] significantly affected egg fertility. However, there is an interesting phenomenon in our study that the effect of delayed mating on females decreased linearly within 4 days, but there was no significant difference among 4 days, 6 days and 8 days.…”

“…A delay in mating will often affect the reproductive physiology and lead to decreased production and adaptability of an insect's progeny [39]. This phenomenon has been shown to exist in many species [35,[40][41][42][43]. Due to the effects generated by sex pheromones, both males and females have readily identifiable targets for their selection of mates [32,33,[44][45][46][47].…”