Aphid midge

Aphidoletes aphidimyza

Aphidoletes aphidimyza is a small, delicate midge , the adults of which are approximately 2.5 mm long, with relatively long legs and antennae. The adults feed on
aphid honeydew and are mainly nocturnal, becoming active at dusk; during the day they tend to rest amongst leaves. The minute orange eggs are Iaid on the leaf surface amongst aphid colonies, and all of the larval stages prey on aphids. They feed by injecting a paralyzing toxin into the leg of the target aphid, and then use their hook-like mouthparts to suck out the aphid’s body fluids, eventually leaving little more than a dry husk. When fully mature, the larvae drop to the soil surface, where they form a cocoon Within the top 1-2 cm (0.5″) in which they pupate. This aspect of their behavior may be disrupted if much of the floor area is covered with impermeable materials such as concrete or weed-suppressing fabric.  Aphidoletes aphidimyza has been recorded attacking more than 70 different species of aphids (including most of those commonly found in glasshouse crops), with the cotton-melon aphid (Aphis gossypii) being a highly preferred species. Larvae will also attack nymphs of the cannabis aphid (Phorodon cannabis).

Adult emergence from pupal cocoons typically begins at dusk (i.e_, when the light intensity gradually declines), and is largely complete by midnight. Most adults will mate on the night on which they emerge, seeking out spider webs or similar fine supporting structures to which they can cling. Egg-laying also takes place mainly at night.  Despite their delicate appearance, the adults have quite a high searching capacity and can disperse at least 45 m (approximately 150 ft) from their release point.

Optimal conditions for this species are temperatures of 20—25°C (68—77°F) with a relative humidity of 70% or higher (the pupae in particular are very sensitive to Iow humidity).
Note that, in autumn, larvae exposed to short days and reduced temperatures may enter diapause, resulting in delayed or reduced emergence from the pupal stage. The critical day-length at which this occurs depends on temperature, but at a night-time temperature of 20°C, will vary from 14—16 hours. However, raising the night-time temperature or adding even quite Iow levels of supplemental light can prevent or reduce the onset of diapause. If using supplemental lighting for this purpose, it is best to increase the day-length by adding extra light in the morning rather than the evening, so as to preserve the natural ‘dusk’ that regulates adult activity.