Egg distribution patterns in the almond seed wasp,Eurytoma amygdali |
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Authors: | N A Kouloussis and B I Katsoyannos |
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Institution: | (1) Laboratory of Applied Zoology and Parasitology, University of Thessaloniki, Department of Agriculture, 540 06 Thessaloniki, Greece |
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Abstract: | The egg distribution patterns ofEurytoma amygdali Enderlein (Hymenoptera, Eurytomidae), which oviposits singly in green, developing almonds, were studied in the laboratory
and in the field. In the laboratory, individual females were caged with a number of almonds and the eggs deposited in each
fruit were counted. In the field, eggs were censused in almonds of different varieties at regular intervals, over four seasons
(1988–91). In the susceptible ‘Retsou’ variety, eggs were uniformly distributed among fruits, both in the laboratory and in
the field, as long as the mean number of eggs per almond was ≤2.5. When the mean number of eggs per almond was higher the
egg distributions were random. This suggests that, up to a certain level of infestation, females were able to assess egg load
of fruits and oviposit in the less infested ones. The main factor enabling the females to discriminate and select the less
infested almonds for oviposition is probably a host-marking pheromone. In 1990, the same patterns of egg distribution were
observed in samples taken from 5 other almond varieties that are not as susceptible as Retsou and have thicker pericarp and
harder endocarp. In 1991 however, when fruits developed more rapidly than in 1990, egg distributions in 3 of these 5 varieties
(Truoito, Ai, and Marcona) were not uniform. Although the mean number of eggs per fruit was low (1.2–2.0), many fruits of
these varieties contained no eggs. This suggests that, in some less susceptible varieties, egg distribution might also be
affected by certain fruit parameters, unfavourable for oviposition, related to the pericarp thickness and endocarp hardness. |
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Keywords: | Eurytoma amygdali Hymenoptera Eurytomidae egg distribution superparasitism host discrimination oviposition behaviour |
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