Les variations pondérales du tissu adipeux et des ovaires, et les variations de longueur des ovocytes, chez Ips sexdentatus Boern (Coleoptera : Scolytidae) ; relations avec le parasitisme par les Nématodes

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Abstract
Variations in fat body and ovary weights as well as length of the most mature oocyte, were studied in Ips sexdentatus, from the end of the maturation of pre-swarming to the 24th h after the copulation. In healthy insects the weight of the ovaries and the size of the terminal oocyte grew until swarming, but declined slightly at the 3rd h after copulation; growth recovers afterwards, slowly at first, then very steeply after the 12th h. The fat body atrophies at swarming, but grows distinctly at the 6th h; its weight decreases markedly at the 12th and 18th h, then grows again considerably at the 24th h. The variations in weight of the ovaries (and of the size of the terminal oocyte) may be compared with that of the fat body, the delay in the response of the ovaries is taken into account. This combined variations may coincide with important periods of the biology of the bark-beetle: swarming, slow then steep maturation of the ovaries, oviposition. Insects parasitized by the nematodes Parasitaphelenchus sp., P. sexdentati (Fuchs 1937) Ruehm 1956 and Contortylenchus diplogaster (V. Lins 1890) Ruehm 1956, the fat body and the ovaries are always smaller, and the terminal oocyte less developed than in the healthy insects. Moreover, the fat body of the infected insects cannot accumulate reserves for the maturation of the oocytes. The resultant delay in maturation of oocytes might explain the important reduction of oviposition in parasitized insects. The effect of the nematodes on the ovaries of I. sexdentatus might be indirect, the direct effect being related to the fat body or to the blood. The abdominal fat body seems to be more affected by parasitism than the prothoracic gland.

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