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

Authors: PAUL, RYAN - Oregon State University; ABRAM, PAUL - Agri Food - Canada; Lee, Jana

Submitted to: Ecological Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/14/2022
Publication Date: 6/14/2022
Citation: Paul, R.L., Abram, P.K., Lee, J.C. 2022. Host patch quality increases parasitoid locomotor activity despite risk of egg limitation. Ecological Entomology. 47(5):810-821. https://doi.org/10.1111/een.13171.
DOI: https://doi.org/10.1111/een.13171

Interpretive Summary: Insects use daylight, their internal circadian rhythm, and environmental cues to regulate whether they are active. Females may adjust activity to balance the risks of depleting eggs and running out of time. Females with few eggs should lower their activity or else they will encounter hosts and have no eggs available to lay. We tested this relationship with the Samurai wasp, a parasitoid that attacks brown marmorated stink bug eggs. At close range, wasps mainly find host eggs by walking. Females increased their rate of walking as they aged and matured more eggs. This delay in activity prevents them from encountering stink bug eggs when they don't have enough eggs to lay in the full cluster of 28 stink bug eggs. Contrary to expectations, females which laid many eggs still walked more for three days following laying eggs. This change in behavior may occur so parasitoids can take advantage of rich environments even though they risk depleting their eggs. For practical application, this may mean that releases of aged wasps will be more beneficial as they are actively finding hosts. Released young wasps may not be active right away, and risk dying in the field due to predation or environmental stress.

Technical Abstract: Insects use a combination of photoperiod, endogenous circadian rhythms, and physiological and environmental cues to regulate their patterns of activity and rest. For females, activity patterns may be adjusted to balance the risks of egg and time limitation. Theory predicts that females with low egg may reduce foraging to lower risk of egg limitation. As a result, synovigenic species which emerge with a low number of available eggs, may limit forage in response to their low egg loads. We tested this relationship between egg load and foraging activity using the egg parasitoid, Trissolcus japonicus. We used activity monitors to measure daily activity patterns separately from exposure to host cues. Parasitoid activity increased with age in parallel with egg maturation. Wasps reached peak activity and maximum egg load both around six days after emergence. One-day old wasps began activity later in the day and reached lower peak intensity of activity compared to 7-day old females. We also measured whether egg depletion from oviposition experience would reduce activity in response to low egg loads. Contrary to expectations, females which laid many offspring increased their activity for up to three days following host experience. Delays in early life activity may allow parasitoids to avoid the risk of egg limitation by reducing likelihood of encounters with host egg masses they could not fully exploit. However, experiencing a high-quality patch can increase parasitoid activity to take advantage of rich environments even at the risk of transient egg limitation. Our study demonstrates that parasitoids can adjust their activity through increases in the length and intensity of active periods in response to both physiological and environmental conditions. Plastic responses in activity patterns may allow parasitoids to minimize foraging costs and decrease likelihood of egg limitation in low quality environments.