Preliminary Evaluation of Drop Cloth Sampling Efficiency for Lygus Adults In Cotton

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 in California cotton, the drop cloth is often used in other production regions and may be more effective for sampling nymphs than the sweep net. Methodology for mark-release-recapture studies of nymphs has not been developed, but such methods for adult lygus are well understood. 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 with fingernail polish to facilitate identification and prevent flight, were released into 1-m sample rows at two times, 1) on the evening before drop cloth samples were collected (PM), and 2) immediately before sampling (AM). A completely randomized design was used with two release times and four replications. The experiment was repeated three times in a field of Acala cotton, and twice in a field of Pima cotton. Recovery of marked bugs from Acala cotton tended to be higher than from Pima cotton. Also, no differences in collection efficiency were observed between dates or times of release in Acala cotton, whereas in Pima cotton collection efficiency was lowest on the second sample date and for the AM releases. Collection efficiency was <100 percent in either cotton type. Observations indicated bugs not collected by the drop cloth were either not dislodged from the sampled plants, or were dislodged onto surrounding plants or the soil surface.