Preliminary evaluation of drop cloth sampling efficiency for lygus adults in cotton

Authors: Spurgeon, Dale; Cooper, William - Rodney

Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: 1/7/2011
Publication Date: 4/25/2011
Citation: Spurgeon, D.W., Cooper, W.R. 2011. Preliminary evaluation of drop cloth sampling efficiency for lygus adults in cotton. National Cotton Council, Memphis, TN. pp. 804-809.

Interpretive Summary: Lygus bugs (the western tarnished plant bug in the West, the tarnished plant bug in the Southeast) represent the most important pest complex in US cotton. Although the sweep net is commonly used for sampling lygus in California cotton, the drop cloth may be a more effective method for sampling nymphs (the immature stages of lygus). We recently developed an approach for evaluating sampling methods in which known numbers of adult lygus, marked so they cannot fly, are released into rows to be sampled. The ability to sample known population levels makes sampling evaluations straightforward. However, no similar method is available for nymphs. Therefore, we used marked adult lygus to evaluate the drop cloth in an effort to gain insights that will be useful in designing evaluations of the drop cloth for sampling nymphs. Marked bugs were released into sample rows in the evening, and into different sample rows on the following morning. The cotton was sampled about 1 hour after the morning releases. In Upland cotton, which had a relatively simple canopy structure, the numbers of marked lygus captured on the drop cloth were similar among sample dates and between release times. In Pima cotton, which had a more complex canopy, drop cloth effectiveness declined as plant canopy width increased, and when the bugs were released in the morning. Less than 80% of marked bugs were recovered from either cotton type. We observed that many of the marked bugs were dislodged onto the soil or surrounding plants, and therefore were not collected by the drop cloth. The loss of these marked bugs was pronounced in plants with a broad canopy. These results indicate that future studies should not use release times close to the time of sampling, and that effort should be made to account for bugs dislodged from the plants but not collected on the drop cloth.

Technical Abstract: The western tarnished plant bug, Lygus hesperus Knight, is a key pest of cotton in western production regions. Although the sweep net is the predominant sampling method used for lygus in California cotton, the drop cloth is used in other regions and may be more effective than the sweep net for sampling nymphs. Methodology for mark-release-recapture studies of nymphs has not been developed, but such methods for adult lygus are available. We evaluated the collection efficiency of the standard 1-m drop cloth against marked and released adults to gain insights into the optimal design of subsequent studies of nymphs. Adult lygus, marked to facilitate identification and prevent flight, were released into 1-m sample rows either 1) on the evening before drop cloth samples were collected (PM), or 2) about 1 h before sampling (AM). A completely randomized design was used with two release times and four replications. The experiment was conducted on three dates in Acala cotton, and on two dates in Pima cotton. In Acala cotton, captures of marked bugs were similar among combinations of sample dates and release times. In Pima cotton, captures of marked bugs were lowest on the second sample date and for AM releases. Recovery of marked bugs on the drop cloth was <80% regardless of cotton type. Additional searches indicated some bugs were not dislodged from the sampled plants, or were dislodged onto the surrounding plants or soil. These results illustrate the importance of allowing sufficient time between bug release and sampling, and suggest a need to account for bugs dislodged from the plants but not collected on the drop cloth.