Are the effects of hunger stage-specific? A case study in an aphidophagous ladybird beetle

Food availability is a fundamental factor determining an animal's potential fitness. Carry-over effects of food limitation from development to adulthood are known to influence reproduction, ageing, and tolerance to stress. We have examined the effect of stage-specific variation (before adult emergence or pre-emergence, post-emergence and post-mating) in food availability in Propylea dissecta (Mulsant). Larvae were reared separately on two different pre-emergence food regimes (abundant or restricted) until pupation. Newly emerged adults were further split into two groups and placed on abundant or restricted post-emergence regimes. After mating, females were split and reared on any one of two post-mating regimes. The results revealed that: (i) time to commence mating declined with increased food availability in pre- and post-emergence stages, (ii) mating duration increased with food availability post-emergence, (iii) highest reproduction output was observed in individuals who had abundant food pre- and post-emergence. However, food availability at the time of oviposition also had a strong influence on fecundity. Solo bouts of scarcity, regardless of which stage suffered them, were effectively managed in at least two of the three stages (pre-emergence, post-emergence, post-mating) had abundant food.

Slow and fast development in two aphidophagous ladybirds on scarce and abundant prey supply

Developmental rates are highly variable, both within and between genotypes and populations. But the rationale for two differential (slow and fast) developmental rates within same cohort under varying prey supply has yet not been explored. For this purpose, we investigated the effect of scarce and abundant prey supply on slow and fast development at 27°C in two aphidophagous ladybirds, Menochilus sexmaculatus (Fabricius) and Propylea dissecta (Mulsant) and its effect on their body mass and reproductive attributes. The ladybirds were provided with scarce and abundant supply of Aphis craccivora Koch under standardized abiotic conditions in the laboratory. A clear bimodal (two peaks, where the first peak represented the fast developing individuals and the second peak slow developing individuals) pattern of distribution for both prey supplies was obtained, which got skewed with change in prey supply. On abundant prey supply, more fast developing individuals (139 M. sexmaculatus and 123 P. dissecta) were found and less (46 M. sexmaculatus and 36 P. dissecta) on scarce prey supply. Slow developing individuals had female biased sex ratio, higher longevity and lower body mass. Fast developing females laid higher number of eggs with higher egg viability. Results of the study are indicative of occurrence and constancy of the slow and fast developing individuals in the egg batch.

Effect of photoperiod on slow and fast developing individuals in aphidophagous ladybirds, Menochilus sexmaculatus and Propylea dissecta (Coleoptera: Coccinellidae)

The effects of environmental parameters on insect development have been studied extensively. But the reasons for 2 differential developmental rates within same cohort under varying environmental factors have not been explored. For the purpose, in this study the existence and stability of slow and fast development under 5 photoperiods (i.e., 8L: 16D, 10L : 14D, 12L : 12D, 14L : 10D and 16L : 8D; light and dark hours per day) and its effect on body mass and reproductive attributes in 2 aphidophagous ladybirds, Menochilus sexmaculatus (Fabricius) and Propylea dissecta (Mulsant) was examined on Aphis craccivora Koch at 27 ± 1 °C temperature. A clear bimodal (2 peaks, where the first peak represented the fast developing and the 2nd peak slow developing individuals) pattern of distribution at each photoperiod was found. The proportion of slow and fast developing individuals in a cohort differed with photoperiods. The slow developing individuals were more in numbers at 8L : 16D, in equal numbers at 14L : 10D and in less numbers at 16L: 8D, indicating that the variation in emergence was owing to exogenous cues influenced differential rates of mortality. Slow developing individuals had female biased sex ratio, higher longevity and lower body mass than fast developing individuals. Fast developing females laid higher numbers of eggs with higher egg viability than slow developing females. Study of such variations in development at different photoperiods is helpful to understand its role in the development of insects particularly ladybirds and permits the selection of fast developing bioagents for their use in biocontrol of pest species.

Are thermal constants constant? A test using two species of ladybird

There is a controversy about whether the thermal constants, lower developmental threshold, rate of development and corresponding degree days required for development, change when a species is reared under different developmental conditions. We present a more precise way of measuring these constants using the linear relationship between the rate of development and temperature. First we use the equation proposed by Ikemoto and Takai (2000) to determine the linear phase of development and then a generalised linear model having a different variance at low and high temperatures, specific for each condition, to estimate the parameters of the linear relationship. Using this method, we show that providing the difference in food quality is sufficiently great, an aphidophagous ladybird develops significantly faster and starts developing at a significantly lower temperature on a good than on a poor quality diet. Adaptive significance of the thermal constants not remaining constant is discussed in terms of a trade-off between growth and rate of development, when temperature and food quality varies.