Dietary conditioning on aphids and conspecific eggs in the ladybird Menochilus sexmaculatus Fabricius influences cannibalistic food choices in subsequent generations

Menochilus sexmaculatus, a generalist aphidophagous ladybird beetle, is one of the potential biocontrol agents of multiple aphid species. This beetle exhibits cannibalism among different life stages. A laboratory experiment was conducted by conditioning the larvae and adults on their natural prey that is aphids, or the conspecific eggs for five generations to assess whether cannibalism was affected by prior cannibalistic experiences or not. Adults of the fifth generation were provided with a choice of aphids and eggs. The time of first prey encounter and prey first encountered along with latency to consume prey and prey first consumed were recorded. Non-cannibalistic individuals preferred aphids over eggs, while cannibalistic individuals showed no preference. The time of first prey encounter and consumption were similar for aphids and eggs irrespective of the diet they were reared on. To assess the long-term effects, offspring developmental duration and body weight were recorded across generations. Similar developmental duration of immature stages was recorded in the first and second generations of cannibalistic and non-cannibalistic lines; however, prolonged developmental duration was recorded in cannibalistic lines when compared with non-cannibalistic ones of later generations. Offspring of later generations developed faster in both lines. The offspring body weight of the second and fourth generations of both lines was found to be similar. However, a decline in body weight was recorded in cannibalistic offspring of the first, third and fifth generations when compared with non-cannibalistic ones. A decline in the body weight of offspring across generations was observed in both lines. The findings suggest that M. sexmaculatus rearing diet influences its preference for prey and that long-term dietary conditioning can affect different fitness components. This could potentially reduce their effectiveness in biocontrol.