THE BIOLOGICAL INDICATORS OF IMMUNE RESPONSE IN TWO INSECTS
Haas, Eric J.
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We aim to elucidate the role of eicosanoids in cellular immunity in the squash bug, Anasa tristis. Squash bugs are significant pest insects that cause major crop damage throughout the Midwest each year. Currently we are assaying the immune response of squash bugs to bacterial challenge by the pathogen Serratia marcescens by documenting hemocyte proliferation, microaggreagate formation, and nodulation in comparison to control insects. In addition to a bacterial challenge, we inject the eicosanoid biosynthesis inhibitor indomethacin to observe the potential effects on the immune response. Assays were also performed on the spined soldier bug, Podisus maculiventris, during periods when squash bugs were unavailable due to diapause. Eleven of 31 challenged squash bugs (35.5%) showed nodulation. The average count per challenged bug was 190 hemocytes and 2.56 microaggregates. This compared to 1 out of the 11 insects with nodulation (9.09%), and an average count of 145 hemocytes and 0.33 microaggregates in the control squash bugs. Of 14 challenged spined soldier bugs, 1 showed nodulation (7.14%) whereas two of 17 control insects showed nodules (11.8%). The hemocyte count was 2820 for challenged spined soldier bugs compared to 1210 in controls. Preliminary experiments with indomethacin showed reduced nodulation, microaggregate formation and hemocytes numbers in spined soldier bugs. More experiments are warranted to determine the overall effect. The bacteria, S. marcenscens, induced an immune response in both types of insects. The challenged squash bugs generally showed higher levels of the indicators of immunity that we chose. These results may establish a baseline for subsequent studies.