Hypera postica (Gyllenhal)
[Also known as Hypera variabilis Herbst)
Taxonomic placing: Insecta, Holometabola, Coleoptera, Curculionidae.
Common name: Alfalfa or clover or lucerne weevil.
Geographical distribution: North America, North Africa, Europe, and Middle East to Iran.
Morphology: Adults brown to black, about 5-7 mm long, with pale stripes along the thorax that extent onto the elytra. Larvae apodous, 10-12 mm in length, whitish, with a brown head,.
Host plants: Some leguminous crops, especially Medicago, and related genera, like Melilotus, Trifolium, and Trigonella.
Life cycle: The adults appear in winter, laying up to 1,500 eggs /female. The hatching larvae feed on the host leaves, at times completely devouring them. They pupate on the ground within woven cocoons; the emerging adults aestivate during summer in soil cracks and resume activity next winter. They are long-lived and usually raise only a single annual generation. Several strains of this beetle that differ in behavior, susceptibility to parasites, and in subtle morphological differences, occur in North America, but all are considered to be the same species.
Economic importance: This pest causes much damage to major forage crops in many parts of the world. Both the larvae and the adults feed on the foliage, the larvae causing most damage. Injured leaves dry quickly, and heavily-damaged alfalfa fields appear grayish. The increase in irrigated forage areas has in turn engendered the increases in clover weevil numbers and damage.
Management
Monitoring: Early season larval damage may be detected by finding minute holes in leaf terminals. Adults can be monitored by the shake-bucket method and by using a sweep-nets in the field.
Horticultural practices: Early harvesting is very effective for reducing pest numbers; such harvesting when weevil populations are high will decreasing weevil densities.
Biological control: The pest is attacked by several hymenopterous parasitoids, of which Bathyplectes curculionis (Thomson) (Ichneumonidae) is the more common. The weevil is also attacked by various entomopathogenic fungi. In some regions these antagonists seriously decrease the pest’s damage, thereby reducing the need for insecticides in alfalfa production.
References
Ben-Ze’ev, I. and Kenneth, R.G. 1980. Zoophthora phytonomi and Conidiobolus osmodes (Zygomycetes: Entomophthoraceae), two pathogens of Hypera species (Col.: Curculionidae) coincidental in time and place. Entomophaga 25: 171-186.
Bundy, C.S., Smith, P.F., English, L.M., Sutton, D. and Hanson, S. 2005. Strain distribution of alfalfa weevil (Coleoptera: Curculionidae) in an intergrade zone. Journal of Economic Entomology 98: 2028-32.
Böttger, J.A.A., Bundy, C.S., Oesterle, N. and Hanson, S.F. 2013. Phylogenetic analysis of the alfalfa weevil complex (Coleoptera: Curculionidae) in North America. Journal of Economic Entomology 106: 426-36.
Dysart, J.R. and Day, W.H. 1976. Release and recovery of introduced parasites of the alfalfa weevil in eastern North America. Agricultural Research Service, USDA Product Research Report 167: 61 p.
Hoff, K.M., Brewer, M.J. and Blodgett, S.L. 2002. Alfalfa weevil (Coleoptera: Curculionidae) larval sampling: comparison of shake-bucket and sweep-net methods and effect of training. Journal of Economic Entomology 95: 748-753.
Malamed-Madjar, V. 1967. The phenology of the alfalfa weevil, Hypera variabilis Hbst. in Israel. Israel Journal of Entomology 2: 29-36.
Moradi-Vajargah, M., Golizadeh, A., Rafiee-Dastjerdi, H., Zalucki, M.P., Hassanpour, M. and Naseri, B. 2011. Population density and spatial distribution pattern of Hypera postica (Coleoptera: Curculionidae) in Ardabil, Iran. Notulae Botanicae Horti Agrobotanici Cluj-Napoca 39(2): 42-48.
Radcliffe, E.B. and Flanders, K.L. 1998. Biological control of alfalfa weevil in North America. Integrated Pest Management Reviews 3: 225–242.
Rotrekl, J. 1993. Contribution to the bionomics of the lucerne weevil (Hypera variabilis Hbst.) on lucerne (Medicago sativa L.). Ochrana Rostlin 29: 293-301.