Eslin P, Prévost G
Laboratoire de Biologie des Entomophages, Université de Picardie-Jules Verne, 33 rue Saint Leu, 80 039 Amiens cedex, France
J Insect Physiol. 2000 Aug 1;46(8):1161-1167. doi: 10.1016/s0022-1910(99)00227-9.
The hymenopteran Asobara tabida Nees (Braconidae, Alysiinae) develops as a solitary endophagous parasite in larvae of several Drosophila species. Most A. tabida eggs possess a sticky chorion which attaches to the tissue of the host organs within a few hours following oviposition. A. tabida sticky eggs usually avoid encapsulation, though the probability of survival decreases in hosts carrying a larger number of circulating hemocytes. Here, we hypothesized that the elicitation of the encapsulation reaction may result from a race between two phenomena: the host's hemocytic reaction and the embedment of the parasitic egg within the host tissues. In order to test this hypothesis, we measured the speed of capsule formation in D. melanogaster larvae of different ages, knowing that the number of circulating hemocytes increases with the age of the larvae. Using a non-virulent A. tabida strain, the eggs of which do not attach to the host tissue, we found that the speed of capsule formation increased correlatively with the age of the D. melanogaster larva. Therefore, the hypothesis of a physiological race between host's immunity defenses and parasite's avoidance of host's defenses is strongly supported by our results. Also, A. tabida eggs which attach to the host's tissue before the attack by the hemocytes has taken place may be considered as a strategy of passive evasion from encapsulation.
膜翅目昆虫塔比阿索芭拉（Asobara tabida Nees，茧蜂科，阿丽茧蜂亚科）作为几种果蝇幼虫体内的单寄生内寄生性寄生虫发育。大多数塔比阿索芭拉的卵具有粘性卵壳，产卵后数小时内会附着在宿主器官组织上。塔比阿索芭拉的粘性卵通常能避免被包囊化，不过在携带较多循环血细胞的宿主中存活概率会降低。在此，我们假设包囊化反应的引发可能源于两种现象之间的竞争：宿主的血细胞反应以及寄生卵在宿主组织内的嵌入。为了验证这一假设，我们测量了不同年龄黑腹果蝇幼虫中包囊形成的速度，因为已知循环血细胞的数量会随着幼虫年龄的增长而增加。使用一种无毒的塔比阿索芭拉菌株，其卵不会附着在宿主组织上，我们发现包囊形成的速度与黑腹果蝇幼虫的年龄呈正相关。因此，我们的结果有力地支持了宿主免疫防御与寄生虫逃避宿主防御之间存在生理竞争的假设。此外，在血细胞攻击发生之前就附着在宿主组织上的塔比阿索芭拉卵可被视为一种被动逃避包囊化的策略。
