1. The Argentine ant, Linepithema humile , tends honeydew-excreting homopterans and can disrupt the activity of their natural enemies. This mutualism is often cited for increases in homopteran densities; however, the ant's impact on natural enemies may be only one of several effects of ant tending that alters insect densities. To test for the variable impacts of ants, mealybug and natural enemy densities were monitored on ant-tended and ant-excluded vines in two California vineyard regions.2. Ant tending increased densities of the obscure mealybug, Pseudococcus viburni , and lowered densities of its encyrtid parasitoids Pseudaphycus flavidulus and Leptomastix epona . Differences in parasitoid recovery rates suggest that P. flavidulus was better able to forage on ant-tended vines than L. epona .3. Densities of a coccinellid predator, Cryptolaemus montrouzieri , were higher on ant-tended vines, where there were more mealybugs. Together with behavioural observations, the results showed that this predator can forage in patches of ant-tended mealybugs, and that it effectively mimics mealybugs to avoid disturbance by ants.4. Ant tending increased densities of the grape mealybug, Pseudococcus maritimus , by increasing the number of surviving first-instar mealybugs. Parasitoids were nearly absent from the vineyard infested with P. maritimus . Therefore, ants improved either mealybug habitat or fitness.5. There was no difference in mealybug distribution or seasonal development patterns on ant-tended and ant-excluded vines, indicating that ants did not move mealybugs to better feeding locations or create a spatial refuge from natural enemies.6. Results showed that while Argentine ants were clearly associated with increased mealybug densities, it is not a simple matter of disrupting natural enemies. Instead, ant tending includes benefits independent of the effect on natural enemies. Moreover, the effects on different natural enemy species varied, as some species thrive in the presence of ants.

Planning (FWQP) series, developed for a short course that provides training for growers of irrigated crops who are interested in implementing water quality protection practices. The short course teaches the basic concepts of watersheds, nonpoint source pollution (NPS), self-assessment techniques, and evaluation techniques. Management goals and practices are presented for a variety of cropping systems.

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There is significant interest in nonpoint source (NPS) pollution monitoring within California' s agricultural community. This interest reflects growers' awareness of water quality issues related to nonpoint source pollution. Regulatory agencies and citizen monitoring groups are involved in controlled monitoring studies of nonpoint source pollution in many of California' s watersheds. In most cases, this type of monitoring is beyond the finances, labor resources, technical expertise, and needs of individual growers. A simple program can be useful for self-evaluation, however, and particularly for evaluation of the effectiveness of a grower' s management practices. The purpose of this publication is to familiarize growers with the basics of self-evaluation.A valid evaluation design is necessary if you are going to identify the changes to water quality that result from modifications to farming operations. Evaluation should answer two questions:• Is water quality degraded as a result of farming operations?• If water quality is degraded, is the water quality improved by subsequent changes in farming operations?

This FACT SHEET is part of the Farm Water Quality Planning (FWQP) series, developed for a short course that provides training for growers of irrigated crops who are interested in implementing water quality protection practices. The short course teaches the basic concepts of watersheds, nonpoint source pollution (NPS), self-assessment techniques, and evaluation techniques. Management goals and practices are presented for a variety of cropping systems.