Gray Bristle Weevil (Sitona Crinitus)

Pest Type: Bean Pest

Row: Coleoptera – Coleoptera

Family: Weevils – Curculionidae

Distributed mainly in the forest-steppe zone, in a smaller amount – in the steppe. It damages one-year and perennial legumes: peas, beans, lentils, lupins, clovers, alfalfa, sainfoin, sweet clover, wild legumes.

Beetle 2.8–4.5 mm in size; elytra in posterior half with long bright setae. The eyes are unevenly bulging. Pronotum with three bright oblong stripes. An egg 0.2-0.3 mm in size, first yellow-white, then blackens. Larva – 4-5 mm, curved, whitish with a light brown head, body covered with long reddish hairs. Pupa – 4.5-6 mm, pale yellow.

Beetles winter in the soil, mainly in the fields of leguminous plants, where they were fed in summer and autumn. In crop rotation, legumes are the usual wintering places. Beetles awaken at an air temperature of 3-4 ° C, are activated at 12-14 ° C and begin to fly at 13-17 ° C. During the migration period, they populate the stairs of one, two and perennial plants. In spring, depending on meteorological conditions, the breeding period can last between 5-7 days or last up to 20 days (in conditions of changing and dry weather with a frequent cold snap).

The mass departure of beetles begins in the second half of April, the maximum – in mid-May and ends at the end of this month. Damage the leaves of perennial legumes begin in the first warm spring days. First, the beetles eat little, on the young growing leaves there appear separate indentations, gnawed from the edges. In warm sunny weather, the damage becomes widespread, beetles actively migrate to the stairs of annual and perennial leguminous plants and immediately begin to eat intensely. There have been cases of complete destruction of the leaves on the stairs of peas and other leguminous plants. Egg-laying in the forest-steppe zone of Russia begins only after additional feeding. Females lay eggs on the soil or stalk, as well as on the leaves from which they roll onto the ground after drying. On average, embryonic development lasts 7-8 days. The mass revival of larvae is observed in May – June.

The absence of precipitation during this period leads to a significant decrease in the number of larvae. Larvae feed on balls. For full development, one larva eats the contents of 3-8 tubers, depending on their size. The development of larvae occurs within 40 days. They feed mainly on peas, fodder legumes, lentils, lupins, etc. Pupation begins in the forest-steppe zone in the first half of June, in years with a cold spring – in the second half of this month. The bulk of the pupae is at a depth of 10-12 cm. The pupal stage lasts 9-13 days. A new generation of beetles emerges at the end of the second – at the beginning of the third decades of June, in the steppe zone – at the end of May – the first half of June. The full development cycle is completed in 45-60 days. Young beetles migrate to plants with juicy green organs and immediately begin to feed.

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