2009 Annual Report
1a.Objectives (from AD-416)
Establish baseline responses to insecticides where feasible and evaluate longer term performance to safeguard against resistance development. Incorporate resistance management strategies into pest management programs for particular pests of cotton and associated crops including silverleaf whitefly, glassy-winged sharpshooter, and Lygus spp.
1b.Approach (from AD-416)
Develop bioassay methods for various insect pests that realistically depict the type of exposures that occur in the field. Collect target pests in their crop habitat and establish and maintain cultures for repetitive testing. Evaluate relative susceptibilities to crucial insecticides by examining dose-mortality responses of immature and adults stages. Determine stability of resistance when it occurs in populations and formulate effective strategies for mitigating resistance by incorporating information on resistance stability. Documenst SCA with UC Riverside.
Monitoring populations of B. tabaci for susceptibility to neonicotinoids has been carried out for many years in Maricopa and Yuma, AZ and in the Imperial Valley, CA. Four neonicotinoids (imidacloprid, thiamethoxam, acetamiprid, dinotefuran) continue to play a critical role in the management of B. tabaci in melons and vegetable crops. Their systemic and translaminar mobilities enable long persistence in plants and help to provide extended protection against steady whitefly pressure. However, the decline curve of these active ingredients as they are metabolized in plants is also protracted and therefore provides a wider window over which selection for resistance occurs. Resistance monitoring results for adult whiteflies collected in Yuma and Imperial Valley in 2009 so far do not show any appreciable rise in resistance levels over previous years. The relative performance pattern among the four neonicotinoids in the bioassays also remains similar with imidacloprid and thiamethoxam having a lower killing power than acetamiprid or dinotefuran.
In addition to monitoring resistance to existing commercial compounds, newer experimental chemistry is also being tested to establish baseline responses of whitefly populations. Spirotetramat and pyrifluquinazon are two new insecticides for which baseline bioassays have been conducted over the past two years and continuing to 2009. Commercial registration for spirotetramat in certain crops began in 2008 as demand is increasing for this highly effective insecticide, a lipid synthesis inhibitor that impairs growth and development. In contrast, the mode of action for pyrifluquinazon is not known, yet this compound has a powerful impact on adult whiteflies in lab bioassays and is able to disrupt transmission of plant viruses. We have demonstrated translaminar properties by pyrifluquinazon that translates to long residual activity against whitefly adults. We will soon be testing field-collected samples of adult whiteflies for laboratory bioassay testing that will begin to build the baseline profile for this compound.
Other activities conducted in 2009 include extensive testing of vine mealybug populations infesting grape vineyards throughout much of California. The pest status of this insect continues to grow as more vineyards become infested and the magnitude of infestations increases. This is placing greater pressure on insecticides for managing infestations. Results from 2009 early summer indicate good efficacy by many compounds in controlled bioassays, yet control in the field is not always adequate. This points to the difference between a bioassay result and a field result using the same concentration of a given insecticide. The nature and degree of exposure between the two are likely much different and often incomparable. However, by maintaining constant bioassay conditions, susceptibility changes through time will be revealed in the controlled bioassay and serve as a mechanism for monitoring insecticide resistance.
ADODR monitors progress by site visit and email.