The Alfalfa Weevil (Hypera postica) is among the most important insect defoliators of Alfalfa (Medicago sativa), an important forage crop in many parts of the world. It is believed to be native to Eurasia, but is now far more widely distributed. It was first recorded from the United States in 1904 in Utah and is believed to have been introduced independently in Arizona (reported 1939) and Maryland (reported 1952). A fourth possible strain (or possibly a closely related species) was also detected in New Mexico in 2003. All these introductions appear to represent different strains (perhaps even species) that vary in behavioral, ecological, and physiological characteristics.
Both larval and adult Alfalfa Weevils feed on Alfalfa foliage, but the larvae cause the majority of the damage. Larvae feed initially on the inside of terminal leaves and later move to foliage on the lower portion of the plant. Early season larval damage (from first and second instars) shows up as pinholes in leaf terminals. Leaves are skeletonized as larvae increase in size. Third and fourth instars defoliate plants by feeding between the veins, as well as on the buds and growing tips. Adults generally feed on the leaf margins, which gives the foliage a feathery appearance. Injured leaves dry very quickly, imparting a grayish to whitish cast to a field of Alfalfa. Efforts at biocontrol have met with some success.
The Alfalfa Weevil is a typical oligophagous insect that feeds almost exclusively on leguminous plants of the genus Medicago, although it occasionally may feed on a few species of related genera including Melilotus, Trifolium, and Trigonella (Moradi-Vajargah et al. 2011).
(Cook et al. 2004; Bundy et al. 2005 and references therein)
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