Does being part of a group improve the survival of larval lady beetles?

Background/Question/Methods

Lady beetles are insect predators that typically lay eggs in clusters, and clutch-mates that emerge near to each other might benefit in several ways. For example, lady beetle larvae are attracted to chemicals that are released by damaged prey. Therefore, one potential advantage to larvae emerging as a group is that if one larva captures a prey item, others can share in the meal. While a shared meal likely reduces the per capita food intake of a hatchling, it might also provide enough nutrition to prevent an early death by starvation during an especially vulnerable stage. We manipulated densities of two-spotted lady beetle (Adalia bipunctata) hatchlings to test whether the presence of clutch mates increases probability of capturing prey and the survival of individual hatchlings. In one experiment, we placed a single prey item with densities of lady beetle hatchlings ranging from 1 to 10 in a small arena for 72 hours. Three experiments were performed on individual fava bean plants, with varying densities of prey and lady beetle hatchlings for 5 days. We measured foraging efficiency of the group and lady beetle larvae in the small-arena trials, and the survival of lady beetle larvae in the on-plant trials.

Results/Conclusions

In the small arenas, as the initial density of lady beetle larvae increased, their foraging efficiency increased (logistic regression: z = 3.506, df = 131, p = < 0.001). At the same time, the survival of lady beetle larvae was not affected by their initial density (linear regression: F = 3.318, df = 129, p = 0.071). Our three on-plant experiments were designed to focus on combinations of prey and lady beetle densities that would be most likely to reveal a positive effect of lady beetle clutch mates on each other’s survival. However, in all three sets of on-plant trials, increasing the initial density of lady beetle larvae did not improve the survival of the larvae (representative linear regression: F = 1.892, df = 32, p = 0.178). Therefore, while having more hatchlings in an area improved their collective ability to capture prey, it did not translate into an improvement in lady beetle survival. Understanding the influences on survival of two-spotted lady beetles during their hatchling stage might enhance their use in biological control.