Comparing Natural Parasitism and Resistance with Proxies of Host Immune Response in Lestid Damselflies

Abstract

Commonly used proxies for measuring immune responses in invertebrates include the amount of melanin deposited on nylon inserts and assays of activity of the enzyme phenoloxidase (PO) in the haemolymph. We used these proxies to estimate immunity in unpar- asitized individuals from four Lestid damselfly species from popula- tions with different levels of water mite parasitism. Levels of para- sitism and resistance by hosts were population level estimates from published papers. These parasitism levels were not correlated posi- tively with immune response measured by proxies in the current study. The species with the strongest melanization response to the inserts and the highest PO levels was the one that currently experienced no mite parasitism. The species with the weakest response to the inserts and the lowest PO levels had low current levels of parasitism. The two species that are heavily parasitized had an intermediate response. Natural resistance levels were also not correlated with the response measured by proxies, but the species with a strong response had high levels of resistance in the past. This finding is supported by earlier work done with Lepidoptera in which the most well-defended species currently experience no natural parasitism.