Ayman Mostafa, Lydia Brown, and Peter Ellsworth - University of Arizona; and Vonny Barlow - University of California
The Egyptian alfalfa weevil (EAW), Hypera brunneipennis – the Egyptian strain of H. postica), is a major winter pest of Arizona alfalfa.
EAW adults are one-quarter inch long, gray-brown insects with ridges on the hardened forewings. The adult has a distinct, extended snout which can be confused with the similar clover root curculio (CRC), a non-economic weevil. The CRC weevil is about two-thirds the size of EAW and has a short, blunt snout.
Young EAW larvae are yellow-green with a brown head. The larvae are often difficult to find since they hide in tightly folded young leaves. The older larvae are darker green with a white line down the center of the back and a distinct brown head capsule.
Fully-grown EAW larvae are one-quarter inch long. EAW larvae can be confused with syrphid larvae, a valuable natural enemy which lacks a head capsule on the tapered head, and with lepidopteran larvae which are summer pests with legs and rarely occur simultaneously in the field. The EAW is legless.
EAW is active from December through April. Adults aestivate (summer hibernation) under loose bark or other sheltered places. In late fall or early winter, adults emerge and migrate to alfalfa fields.
Females insert eggs into alfalfa stems. Once hatched, the larvae feed on leaves and terminal buds causing skeletonization, bronzing, and stunted growth. Larvae are the most damaging stage.
Adult EAW weevils also feed on alfalfa leaflets and stems but generally do not cause significant damage. EAW is the most damaging to the second cutting but can also damage the third cutting.
No resistant non-dormant commercial cultivar exists. Varieties with rapid spring growth may be more tolerant of weevil damage.
Early harvesting can mitigate damage but surviving larvae under windrows can reduce growth.
Begin monitoring for EAW when temperatures drop below 42 degrees Fahrenheit (usually in January) with 180-degree sweep net samples from four areas in the field (five sweeps per area) two times a week. Treat when an average of 20 larvae per sweep is found.
If averages of 15 to 20 larvae per sweep are found just prior to harvest, an application of an appropriately short pre-harvest interval insecticide may be needed to reduce damage to regrowth, especially under the windrow.
To view the photos associated with this article, click on this link: http://ag.arizona.edu/crops/cotton/files/EAW_ShortFc.pdf