Analysis of acquirement mechanism for nutritional resource in host-parasitoid interaction

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The nutritional relationship that is established between hosts and their parasites is never simple and often reflects a long co-evolutionary ‘arms-race' between each other. In this arms-race, hosts evolve mechanisms that enable them to escape from their parasites or to eliminate them ; on the other hand, the parasites need to overcome host defenses and utilize the host as a nutritional reservoir. The parasitoid larvae feed selectively on certain host tissues in order to keep a minimal damage to the host. Severe damage of the host during early development may lead to precocious death of the parasitoid. Feeding exclusively on the nutrient-rich hemolymph is one strategy that parasitoid. larvae employed to minimize host damage. Hemolymph retains a high nutritional value since it efficiently retrieves nutrients, which have already been or are to be stored in organs like the fat body via a specialized metabolic pathway, through inhibition of absorption of nutrients by the fat body, or only by slowly reducing the amount of fat body. The koinobiont larvae, however, possess well-developed gut to digest some foods during their late stages. Also, during late larval stages, the parasitoid larvae exhibit rapid growth just prior to pupation. These facts are difficult to explain on the sole basis of nutrient uptake from host hemolymph. Elucidation of how ecto- and endo-parasitic koinobionts utilize the hosts as a food resource will be useful in clarifying the evolution of common or different strategies in koinobionts. We studied strategies that enable parasitoids to ensure a sufficient food resource in both ecto- and endoparasitic koinobionts and explain how the parasitoid larvae utilize the host resource to enhance successful parasitism.