FIELD-SCALE MOVEMENT OF LYGUS BUGS IN ARIZONA COTTON
Ayman Mostafa, University of Arizona
Lygus bugs are major insect pests of cotton in Arizona with potential to affect yield quantity and quality. Dispersal of Lygus bugs is a complicated issue and movement is affected by the bug's age, sex and reproductive status. In Arizona, the inter-field movements of Lygus bugs were studied over large areas. From these early studies, we identified "source" hosts like alfalfa and weeds that readily supply Lygus to "sink" cotton fields. However, very little is known about smaller scale Lygus movement within cotton fields or precisely how they colonize and develop once arriving in individual cotton fields.
Research has shown that egg white, cow milk, or soy proteins can be sprayed in the field using conventional spray equipment to mark insects. In turn, protein-marked insects can be tracked to measure their movements in the field. For this project we propose to measure within field movements of Lygus adults and nymphs with an ultimate goal of developing an understanding that could lead to more efficient detection (sampling) and precise control of Lygus while reducing economic risk.
During the first year of this project, methods development conducted for plot marking, sampling, insect sorting and analysis. Milk (three) and egg proteins (once) were tested in cotton field divided into 66 plots, 40 x 40 ft, on the MAC Research Farm. Active monsoons (3.5 inches of rain at MAC) have compromised the egg protein and one of the milk protein mark residual. The milk protein was detected in 65% of sprayed leaves in marked plots. About 1200 Lygus were recovered from marked and unmarked plots. An average of 17.5% of Lygus bugs collected from different plots in the field was marked by the protein after the first two sprays. The results of the first year of this project indicates proof that the milk protein applied using a commercial sprayer provides good coverage of the canopy as indicated by the percentage of marking cotton leaf discs. The experimental design and procedure are subject to review to refine the plan for 2013 season and evaluate results. Suggested improvements may include: enhance technique to retrieving a large percentage of marked Lygus from the samples, measures to further reduce the risk and confounding factor of secondary transfer, and measures to secure our inferences that retrieved marked Lygus are indeed as a result of insect movement and not due to other uncontrolled factors.