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Animalia >Arthropoda >Insecta >Hymenoptera >Scelionidae >Trissolcus >

This wasp Trissolcus plautiae is the primary wasp that parasitizes eggs of the stinkbug Plautia crossota stali. When a wasp encounters a stinkbug egg, it shows a series of oviposition behaviors. It first taps the egg with its antennae and determines whether it is of the right host species and whether it has already been parasitized. It then proceeds to insertion of the ovipositor and then to oviposition. After oviposition, it puts an "already-parasitized" mark on the egg by rubbing the egg surface with its ovipositor. Markings like this, in general, are effective in repelling individuals of the same species but are ineffective in repelling individuals of other species. Effectiveness of markings also differs depending on females' experience (i.e., whether they have an egg-laying experience or not) or condition (i.e., whether their egg laying was inhibited or not). In the study of another wasp that parasitizes eggs of a different stinkbug Nezara viridula, it has been suggested that wasps mark eggs with some kind of pheromones.
I analyzed marking behaviors in Trissolcus plautiae and examined marked eggs under SEM. The marker was a thread-like material and was stretched between the tips of projections on the egg surface. Female wasps have hair cells specialized in detecting the presence of the markers in their antennae. The thread-like markers are cut as females tap them, and recognition of markers becomes more and more difficult with more tappings. In cases where an egg was tapped more than a dozen times, recognition seems to have become impossible and more than one wasp oviposited in a single egg. Rinsing an egg with water or organic solvent made thread-like markers stick to the egg surface and diminished the effectiveness of the markers. These results suggested that the thread-like makers that are stretched between the egg-surface projections signal the presence of prior oviposition and that females recognize their presence by hair cells in their antennae. It is possible that the thread-markers may also function as carriers or vectors of pheromones. The thread-like markers are secreted from a tip of a poison gland that reached the tip of the ovipositor.

(Data No.momo050122tp01b)

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