Tychius medicaginis Ch. Brisout - Alfalfa Seed Gall Weevil.
Systematic position.Class Insecta, order Coleoptera, family Curculionidae, genus Tychius Germar. It differs from Tychius aureolus Kiezw. and T. flavus Becker in white lateral band on elytra, from T. junceus Reich. in flattened rostrum and darkened apical part of antennae.
Biological group.Pests of alfalfa seed crops.
Morphology and biology.Body length without head is 2-2.6 mm. Rostrum is moderately stout and elongated, gradually narrowed apicad. Dorsal side of rostrum in preapical part is transversely convex, without carinae and rows of punctures. Apical part of antennal funicle and clava darkened. Eyes are weakly convex. Elytra are oviform, widest in mid length and strongly convex along suture. Dorsum is light-yellow, rarely grayish, with white longitudinal bands on each side of elytra. Body integument is not obscured by overlying scales. Lower margin of male femora has no erect scales. Aedeagus gradually and moderately narrowed apicad.
Distribution.Middle and South Europe, Middle East. In the former USSR, it inhabits the European part northward to Baltic States; the Caucasus, the South of Western Siberia, Middle Asia, and Kazakhstan.
Ecology.Monovoltine species. It hibernates in the soil during adult stage. Medicago falcata, M. sativa, and in lesser degree Melilotus sp. are host plants for the pest. In spring time, adults usually feed on the lower surface of alfalfa leaves. Mating begins in the 2nd half of June. Female gnaws hole in the bud or rarely in the ovary and lays egg. Inflicted damage promotes gall forming on the ovary. Embryogenesis lasts 10 days. Larva feeds on gall tissue; its development takes 12-13 days. From the end of July to the 1st half of August, mature larva gnaw hole outward from the gall and drops to the soil for pupation. Young beetles emerging in summer do not reproduce. After alfalfa mowing, the adults migrate to surrounding fields. Larval parasite Habrocytus sp. (Pteromalidae) infests up to 22% of population.
Economic significance.Damage in the adult and larva stages result in disturbing seed formation. Main damage is observed in steppe zone, where seed yield losses amount to 25%. Medicago falcata is more resistant to the pest than M. sativa. The pest number decreases after multiple mowing of alfalfa. Control measures include distant planting of seed alfalfa from other alfalfa fields. Insecticide treatment is necessary before blossoming of the alfalfa for preservation of insect pollinators.
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