Reproductive Adaptations

It isn't as easy as you would think to find and parasitize a host and Ichneumons know this first hand. Host's have adapted many defensive mechanisms to evade these parasitoids. The most obvious defence is to hide and minimize time out in the open. Wood-boring horntail wasp larva are an exception to this as they are still detected by Megarhyssa macrurus through many inches of wood. Entomologists are still unsure of M. macrurus detects the larva so efficiently.

Other mechanisms of evasion are to get rid of body waste and to avoid plants that have been chewed on already. This ensures there are no visual cues for the parasitoid to track. Behavioural evasion is also a good method to avoid interaction with parasitoids.

Evolutionary defensive adaptations include a thickening of the egg wall and cuticle to make it more difficult for Ichneumons to successfully oviposit the egg into the host, and secretion or consumption of poisonous substances that can poison the eggs or larva in or on the host.

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Ichneumons have adapted along with the host to overcome these defensive mechanisms. Before ovipositing into the host, Ichneumons usually inject secretory products to paralyze the host. This prevents injury while ovipositing the egg.

Another adaptive secretory product is polyDNA virus. This virus replicates using the Ichneumonidae genome, and infects the host's cells causing symptoms that suppress the host's immune system while protecting and benefiting the egg/larva. This adaptation greatly improves the likelihood that the parasitic larva will survival to the pupal stage, but is an unfortunate advantage over the host.