Parasitic wasp

Aphelinus abdominalis

Aphelinus abdominalis is another small parasitic wasp that attacks aphids. The adults are somewhat smaller than the Aphidius species (approximately 1—1.5 mm long), with a dark head and thorax and a yellowish abdomen. This species has quite a broad host range, but in glasshouses is primarily used for managing potato aphid (Macrosiphum euphorbiae) and foxglove aphid (Aulacorthum solani); it will also attack the green peach aphid (Myzus persicae).

As in Aphidius species, a single egg is deposited in the host aphid, and the developing wasp larva feeds on the aphid’s internal tissues until the host dies and the wasp pupates. In this case, however, the dead, ‘mummified’ aphids turn black rather than golden Brown, and the ‘mummies’ may be found at some distance from active aphid colonies, as aphids parasitized by A. abdominalis have a tendency to disperse before the wasp within pupates. When pupation is complete, the newly formed adult wasp emerges by chewing an exit hole in the back of the dead aphid.

Aphelinus differs from the Aphidius species in that the adult females will kill not only the aphids that they parasitize, but also numerous others through the process of ‘host-feeding’; the latter involves puncturing the host with their ovipositor (egg-laying structure) and then feeding on the fluids leaking from the wound. With larger aphid species (such as the potato aphid and foxglove aphid), the youngest aphids (first and second instar nymphs) are usually used for host-feeding, while the second third instar nymphs are the main stages that are actually parasitized.

Aphelinus abdominalis has a longer adult lifespan than the Aphidius wasps (I5—27 days, depending on temperature), but typically lay fewer eggs per day. Nevertheless, a single adult female may parasitize a total of approximately 200 aphids and kill an additional 30—50 through host-feeding. This species performs best at temperatures of 20°C(68°F) or higher. At 20°C, it takes approximately 7 days for the first mummies to form, and an additional 14 days before the new adults emerge. Aphelinus species are not considered Strong fliers and are unlikely to disperse as far from their release points as the Aphidius species.