Pest Type: Pest of perennial bean culture
Row: Coleoptera – Coleoptera
Family: Weevils – Curculionidae
It is widespread in Russia, rarely – in the woodland and Carpathian region, damages alfalfa.
The beetle is 2.1–2.7 mm in size, the pronotum and especially the elytra are densely covered with short round dull and oval scales; on the elytra, they are yellow, wide, chopped off or sharply rounded at the apex; bottom in white-yellow scales; antennae and legs brownish-black. The egg is 0.6 mm in size, short, cigar-shaped, colorless. Larva 3-4 mm long, white, somewhat curved, legless.
Beetles overwinter in the upper soil layer (3-7, sometimes up to 15 cm) on alfalfa crops and in stations of its wild species. Beetles are able to withstand frosts to -30 ° C. After wintering, the beetles leave when the soil warms up to 15-17 ° C (the second half of April – early May), after the growth of alfalfa. Beetles can remain at wintering places for a long time, eating buds, young stems, and leaves. At night and until 9-10 a.m., the beetles hide in cracks and under lumps of soil, under the remains of plants, and only with an increase in air temperature to 20 ° C rise to the top of the plants. Intensive migration up to 5-6 km and more is observed during the budding phase – the beginning of alfalfa flowering. Eggs are laid at the beginning of the formation of the beans. The female places the eggs only on green beans, gnawing a round hole in the bean leaf, in which it lays one, sometimes two or three eggs.
At the end of the laying of eggs, the beetles die and only a few hide in the ground and winter again. Embryonic development lasts 6 to 10 days. The hole quickly overgrows, and the larva feeds on the seeds inside the alfalfa bean. In the forest-steppe, the beginning of egg-laying is observed in the second half of June, massive – at the end of June – the first half of July, when the mass flowering of alfalfa ends. The larva during the development period, which is about 20 days, destroys 2-4 seeds.
During mass reproduction, there may be two, sometimes three, larvae of weevils in a bean. In the second half of June, the larvae complete their development, gnaw a hole in the bean leaf through which they crawl out and fall onto the soil for pupation. In the soil, the larvae form earthen nests, in which they turn into pupae. The development of pupae lasts 5-15 days. Beetles of the new generation remain in the earthen little box until the spring of next year. Earth nests are strong enough and even during plowing remain intact. One generation is developing in a year.
Protective measures. Harrowing crops before the growth of alfalfa or disking on thickened crops. Keeping the distance between the crops of legumes at least 1000 m. When the number is more than 15-25 beetles per 100 strokes of the net on the testes in the phase of stem growth – the budding of alfalfa – the use of insecticides.