Host patch quality increases parasitoid locomotor activity despite risk of egg limitation

Abstract

Abstract Theory predicts that egg load and foraging activity of insects should be positively related. Species that emerge with a low initial egg load and mature additional eggs as they age may limit initial foraging activity to avoid egg limitation. Similarly, females, which deplete their egg supply through oviposition, should decrease activity immediately afterwards and then increase activity as new eggs are matured. The authors used activity monitors to measure daily locomotor activity separately from exposure to host cues with the stink bug egg parasitoid, Trissolcus japonicus. The authors measured activity and egg load as newly emerged wasps aged and tested whether egg depletion from oviposition would reduce activity. Parasitoid activity increased with age in parallel with egg maturation, with both egg load and activity reaching their maximum about 6–7 days after emergence. Newly emerged wasps began activity later in the day and had lower activity intensity compared with older individuals. When given host experience, females that had laid many offspring, and had thus depleted their egg loads, unexpectedly increased their activity for up to 3 days. The present study results challenge the generally accepted positive relationship between foraging activity and egg load, suggesting that this relationship may be secondary to host patch quality. The authors provide evidence that host patch quality can influence not only within‐patch but also between‐patch foraging activity. Plastic responses in activity patterns may allow parasitoids to better exploit rich host environments while minimising foraging costs and decreasing likelihood of egg limitation in low‐quality environments.