The development of Monoctonus paludum Marshall (Hym., Braconidae) in Nasonovia ribis-nigri on lettuce, and immunity reactions in other Lettuce Aphids

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Abstract
Aphids belonging to the species Nasonovia ribis-nigri (Mosley), Aulacorthum circumflexum (Buckt.), Macrosiphum euphorbiae (Thos.), Myzus persicae (Sulz.) and A. solani (Kalt.) were exposed to attack by the parasite, Monoctonus paludum Marshall, and were sectioned and dissected at various time-intervals after attack in order to observe the developmental processes of the parasite.The egg was always laid in the posterior mass of fused ventral nerve ganglia in the thorax of the aphid host.The development of the parasite in N. ribis-nigri, its normal host on lettuce, is described.In the species A. circumflexum the development of the parasite was arrested after approximately 24 hours by the secretion around it of a thin brown capsule formed by certain of the host's blood cells.In the other three species, Macrosiphum euphorbiae, Myzus persicae and A. solani, no capsule formation occurred. The development of the parasite embryos was rather variable in these but it was common for parasites in Macrosiphum euphorbiae to reach the stage normal for 24-hour embryos and for parasites in Myzus persicae and A. solani to reach stages rather less advanced than this before degenerative changes set in.The degenerative changes in the parasite embryos are described for each species of aphid and the nature of these changes is discussed.