Does superparasitism improve host suitability for parasitoid development? A case study in the Microplitis rufiventris-Spodoptera littoralis system |
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Authors: | Wedad E Khafagi Esmat M Hegazi |
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Institution: | (1) Biological Control, Plant Protection Research Institute, Sabahia, Alexandria, Egypt;(2) Department of Economic Entomology, Faculty of Agriculture, Alexandria University, Alexandria, Egypt |
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Abstract: | Superparasitism refers to the oviposition behavior of parasitoid females who lay their eggs in an already parasitized host.
Recent studies have shown that allocation of additional eggs to an already parasitized host may be beneficial under certain
conditions. In the present work, mortality of Microplitis rufiventris wasps was significantly influenced by both host instar of Spodoptera littoralis larvae at parasitism and level of parasitism. In single parasitization, all host instars (first through sixth) were not equally
suitable. Percentage of emergence success of wasp larvae was very high in parasitized first through third (highly suitable
hosts), fell to 60% in the fourth instar (moderate suitable) and sharply decreased in the penultimate (5th) instars (marginally
suitable). Singly parasitized sixth (last) instar hosts produced no wasp larvae (entirely unsuitable), pupated and eclosed
to apparently normal adult moths. The scenario was different under superparasitism, whereas supernumerary individuals in the
highly suitable hosts were almost always killed as first instars, superparasitization in unsuitable hosts (4th through 6th)
had significant increase in number of emergence success of wasp larvae. Also, significantly greater number of parasitoid larvae
successfully developed in unsuitable hosts containing three wasp eggs than counterparts containing two wasp eggs. Moreover,
the development of surplus wasp larvae was siblicidal in earlier instars and nonsiblicidal gregarious one in the penultimate
and last “sixth” instars. It is suggested that the optimal way for M. rufiventris to deal with high quality hosts (early instars) is to lay a single egg, while the optimal way to deal with low quality hosts
(late instars) might be to superparasitize these hosts. |
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Keywords: | Spodoptera littoralis Microplitis rufiventris Superparasitization Parasitoid survival Evolution of gregariousness |
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