Pests
Hypera postica Gyll. - Lucerne weevil.
Systematic position.
Class Insecta, order Coleoptera, family Curculionidae, genus Hypera. Closely related to H. transsylvanicus Petri, misidentification occurs very often.Synonyms.
Phytonomus variabilis Herbst.Biological group.
Pest of lucerne.Morphology and biology.
Body length, 4-5.5 mm. Rostrum almost straight, rather short and thick, frons about 2 times narrower than rostrum. Antennal scape reaching to the middle of eyes. Pronotum broadest near the middle. Body covered with bifid scales. Aedeagus long and narrow, slightly curved dorsoventrally in apical part. Hibernate usually as adults. Feeding, mating and oviposition begin in spring when air temperature are at least 12°c; beetles lay eggs into old green stems or into leaf axils. The first oviposition is possible on warm days during the autumn and winter in southern regions; in early spring abundant oviposition coincides with the beginning of alfalfa vegetation. Female gnaws a cavity in stem, and lays 1-20 eggs. Eggs are yellowish, broadly oval. Fertility is not more than 2500 eggs. Development of eggs lasts 10 to 18 days. After hatching larvae leave the chamber, and are highly mobile, searching for leaf buds. Larvae have 4 instars and develop in 15 to 28 days. At the last (4th) instar larvae are light green with median white line along dorsal side, with body length reaching up to 8 mm. During last instars larvae live openly and make globular white cocoon before pupation. The pupa development lasts 6 to 11 days. Most adults hibernate in the upper layer of soil.Distribution.
Inhabits most parts of West Europe, Canary Islands, northern Africa, Turkey, Israel, Iran, Afghanistan, and was introduced into the USA. In the former USSR it is distributed in Baltic countries, in the south of the European part, the Caucasus and Middle Asia.Ecology.
Almost everywhere monovoltine, a second generation is possible in places only with long summer. Summer diapause is possible during hot months when temperatures exceed 25°. Medicago sativa is the most preferable as host plant. Larvae concentrate at top of plants. Additional feeding of adults is possible on Alhagi camelorum, Robinia pseudoacacia, and on cotton shoots. Population density in nature depends on entomophages and diseases, e.g., egg parasite Anaphoidea luna Girault, larva parasite Canidia curculionis Thoms. (that was introduced into the USA); larvae may also be infected by mycosis of Entomophtora phytonomi Arthur, Tarichium phytonomy Jacz., and adults by Sporotrichium globuliphera Spreg.Economic significance.
Larvae cause the most significant damage to alfalfa, particularly to seed-crops. In the republics of Middle Asia the pest population density reaches to 1500 larvae per 1 sq. m. Alfalfa varieties with early vegetation are the most susceptible. Control measures include harvesting alfalfa when young larvae move out from leaf axils and immediate removal of the yield from fields. Good results are also obtained by disking after cutting alfalfa in early spring, when the plant height reaches 10 to 11 cm. Alfalfa growing in crop rotation is not desirable for more than 5 years.Reference citations:
Shamuratov G.Sh., Deordiev I.T. 1990. Lucerne weevil and decrease of its population. In: G. Sh. Shamuratov, editor. Sbornik nauchn. trudov. Nukus.: Izd. Karakalpakstan. 15-17 pp. (In Russian)Shchegolev V.N., ed. 1955. Agricultural Entomology. Leningrad & Moscow: Gos. Izd. Selskokhoz. Lit. 616 pp. (In Russian)
Yakhontov V.V. 1934. The alfalfa weevil (Phytonomus variabilis Hbst.). Proceedings of Middle Asia Insitute of Cotton Growing. Moscow & Tashkent. 238 pp. (In Russian)
Zaslavskii V.A. 1961. Review of the species of the genus Phytonomus Schonh. (Coleoptera, Curculionidae) in the fauna of the USSR. Entomologicheskoe Obozrenie 60(3): 625-635. (In Russian)