Insect enemies of the lucerne aphid.
Aphis craccivora Koch is an important pest of species of liquorice [Glycyrrhiza spp.] on irrigated lands near Tashkent, in the Soviet Union. The aphid forms large colonies in the inflorescences at the beginning of the flowering period and infestation of plants sometimes reaches 60-75%. As a result, plant development is delayed and some of the buds and flowers fall. The aphid has various natural enemies, and the most important are coccinellid predators, including Coccinella septempunctata L., Synharmonia conglobata (L.), Scymnus subvillosus (Goeze) (Pullus subvillosus) and Stethorus punctillum Weise. The first of these is the most numerous and 10-12 larvae and adults are found on individual inflorescences. The larvae devour 45-50 aphids per day. The second most numerous is Scymnus subvillosus. Syrphids are also common predators of the aphid, larvae of Paragus tibialis (Fall.) being the commonest. They are present from late May or early June, and there are up to 15/10 cm of flower stem. Other syrphids present are Syrphus interrumpens Wlk. and Metasyrphus corollae (F.) (S. corollae). They are quite active, and adults of the former destroy up to 120 aphids/day. Other predators present are Chrysopa septempunctata Wesm. and C. carnea Steph., these being somewhat less numerous than the syrphids. Some control is also afforded by Leucopis sp. and the mite Allothrombium fuliginosum Herm. This last is the earliest predator to appear (in the second ten days of May) and forms colonies of up to 35 individuals; it destroys some 20% of the aphids. However, the most important factor in natural control is the parasite Lysiphlebus fabarum (Marshall), which appears in mid-April, reproduces at a rate parallelling that of the aphid and reaches its peak of activity in June, when it parasitises up to 85% of the aphid population. To conserve these valuable natural enemies, insecticides should be used against the aphid only in cases of absolute necessity.