Evaluation and Calibration of Sampling Methods Used to Estimate Abundance of Alfalfa Weevil Larvae (Coleoptera: Curculionidae)

Three sampling methods for estimating abundance of alfalfa weevil larvae (Hypera postica Gyllenhal) were evaluated for both accuracy and precision. A plastic bag/Tullgren funnel method collected significantly fewer second, third, fourth instar and total larvae than did the bucket-shake method. Calibration equations were developed to convert intensity estimates (alfalfa weevil larvae per alfalfa stem) obtained from the plastic bag/Tullgren funnel method to bucket-shake estimates. Sweep-net sampling produced significantly lower coefficients of variation than both bucket-shake and plastic bag/Tullgren funnel sampling methods, however mean estimates of larval abundance obtained from sweep-net sampling could be reliably converted to bucket-shake estimates for only fourth instar larvae.