Cannibalistic feeding of larval Trichogramma carverae parasitoids in moth eggs
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Wasps of the genus Trichogramma parasitise the eggs of Lepidoptera. They may deposit one or many eggs in each host. Survival is high at low density but reaches a plateau as density increases. To reveal the mechanism by which excess larvae die we chose a lepidopteran host that has flattened, transparent eggs and used video microscopy to record novel feeding behaviours and interactions of larval Trichogramma carverae (Oatman and Pinto) at different densities. Single larvae show a rapid food ingestion phase, followed by a period of extensive saliva release. Ultimately the host egg is completely consumed. The larva then extracts excess moisture from the egg, providing a dry environment for pupation. When multiple larvae are present, the initial scramble for food results in the larvae consuming all of the egg contents early in development. All larvae survive if there is sufficient food for all to reach a threshold developmental stage. If not, physical proximity results in attack and consumption of others, continuing until the surviving larvae reach the threshold stage beyond which attacks seem to be no longer effective. The number of larvae remaining at the end of rapid ingestion dictates how many will survive to emerge as adults.
KeywordsPhysical Attack Developmental Threshold Single Larva Light Brown Apple Moth Urate Cell
Financial support came from an Australian Research Council SPIRT Grant C00107081. L. Heslin is the recipient of an ARC APAI award. We thank Molly Hunter and Gimme Walter for their comments on the manuscript, Dan Papacek (Bugs for Bugs, Mundubbera, Queensland) for supplying T. carverae, Nancy Cunningham (South Australian Research and Development Industry) and Queensland Department of Primary Industries for supplying moths. The experiments comply with the current laws of Australia.
S1. Development of a single T. carverae larva inside an E. postvittana host egg. Individual frames were captured at 10 minute intervals.
S2. Development of multiple T. carverae larva inside an E. postvittana host egg. Five larvae hatch but only two develop to the prepupal stage. Individual frames were captured at 10 minute intervals. Single frames from the movie are depicted in Figure 3.
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