Insect immune defenses include encapsulation and the production of lysozymes and phenoloxidase. However, the highly mobile larvae of parasitoid Ormiine flies (Ormia ochracea) can evade initial encapsulation, and instead co-opt host immune responses to form a critical respiratory funnel connecting them to outside oxygen. Here we ask how field crickets (Teleogryllus oceanicus) respond immunologically to O. ochracea infestation. Host encapsulation and phenoloxidase play important roles in the formation of the respiratory funnel, so we hypothesized that decreases in these immune parameters during infestation may interfere with respiratory funnel formation and increase the likelihood of larval death. Encapsulation ability decreased after infestation with O. ochracea larvae, but phenoloxidase activity increased in both infested crickets and controls, whereas lysozyme activity decreased in infested crickets but remained constant in controls. Hosts with fewer established larvae showed greater decreases in encapsulation, and phenoloxidase activity was positively associated with the degree of larval respiratory funnel melanization. Differences between phenoloxidase and lysozyme activity in infested crickets are consistent with a trade-off within the immune system of hosts, and our results demonstrate the effects of a prior immune challenge on the ability to mount a subsequent response.
Bibliographical noteFunding Information:
Funding for this research was provided by grants from the National Science Foundation and the UCR Academic Senate to M. Zuk. R. Sauvajot and W. Wagner were a great help with obtaining permits and collecting flies, and S. Adamo gave valuable advice on the immune assays. We are particularly grateful to J. Wang for his help with the artificial infestations, and to K. Farooq for assisting with cricket maintenance. Two anonymous reviewers provided helpful comments on the manuscript. Last but not least, we thank C. Hayashi for use of her -80 freezer.
- Insect immunity
- Ormia ochracea
- Respiratory funnel
- Teleogryllus oceanicus