Monitoring Bemisia Susceptibility to Applaud (buprofezin) during the 1998 Cotton Season

Starting in 1993, we developed a field-based protocol for bioassaying sweetpotato whiteflies (SWF) for susceptibility to buprofezin (Applaud®). Since then, we have monitored Arizona SWF populations (up to 5 regions) for susceptibility to Applaud in four out of the last six seasons. We observed no appreciable decrease in susceptibility. Instead, we have observed an increase in susceptibility of present day whiteflies when compared to populations bioassayed in 1993 and 1996, before any Applaud use in the U.S.. This result, however, is likely related to various procedural changes in the bioassay methodology. Nevertheless, our current estimates of whitefly susceptibility are similar to those obtained from various unexposed populations from around the world and to populations we bioassayed in 1997. Differences between our LC50 estimates and those of some other researchers can probably be explained by various procedural differences: 1) method of Applaud application, 2) whitefly stage collected and sources of leaf foliage, and 3) bioassay environmental conditions. Our results also showed each year that Applaud susceptibility does not decline after Applaud application(s) based on commercial paired field comparisons and replicated small and large plot evaluations. In fact, susceptibilities actually marginally increased after an Applaud application. This fact does not alter the recommendation for Arizona to limit Applaud use to one time per crop season, but does provide hope for the development of a sustainable use pattern even if usage continues on non-cotton hosts (i.e., on melons and vegetables under Section 18). Given the tremendous value of this mode of action, however, commodity groups should work together wherever possible to coordinate the usage of this and other valuable compounds so that whitefly generations are not successively exposed to this product

Monitoring Whitefly Susceptibility to Applaud

A bioassay developed by one of the authors (MY) in 1993 was used to monitor susceptibility of sweetpotato whitefly to Applaud in five different field locations. Whitefly populations were exposed to from 0 (untreated fields) to 4 (small plot trial) applications of Applaud. Susceptibilities of whiteflies, as measured by LC₅₀s and LC₉₅s, did not increase with exposure to Applaud (0 to 4 applications) nor since baseline measurements of susceptibility were made in 1993. Under current patterns of use (single use), risk of resistance to Applaud appears to be minimal

Diet-dependent effects of gut bacteria on their insect host: the symbiosis of Erwinia sp. and western flower thrips.

Studies on bacteria in the gut of insect species are numerous, but their focus is hardly ever on the impact on host performance. We showed earlier that Erwinia bacteria occur in the gut of western flower thrips, most probably acquired during feeding. Here, we investigate whether thrips gain a net benefit or pay a net cost because of these gut bacteria. On a diet of cucumber leaves, the time to maturity is shorter and the oviposition rate is higher in thrips with bacteria than in thrips without (aposymbionts). When fed on cucumber leaves and pollen, aposymbionts develop faster and lay more eggs. So Erwinia bacteria benefit or parasitize their thrips hosts depending on the diet, which is in accordance with theoretical predictions for fitness of organisms engaged in symbiotic interactions. Possibly, the transmission of gut bacteria has not become strictly vertical because of this diet-dependent fitness variability

Effect of Diet on Development and Reproduction of Pezothrips kellyanus (Thysanoptera: Thripidae)

The developmental time, fecundity, and longevity of Pezothrips kellyanus (Bagnall) (Thysanoptera: Thripidae) encaged on lemon, Citrus limon (L.) Burm.f., leaves supplied with different food sources (pollen, sucrose, and honey) were compared at 25 degrees C. Only the addition of pollen offered a nutritional benefit for this thrips species. Pollen to the lemon leaf reduced total developmental time from egg to adult from 12.42 to 9.68 d, increased survival from 22.6 to 80.6%, and increased fecundity. When sugar was offered, only 10% of larvae survived. P. kellyanus larvae were unable to grow on lemon leaves as well as when honey was supplied to the leaves (recorded survival was 22.6 and 42.86%, respectively), and adult females were slightly able to reproduce (1.4 and 4.2 larvae per female, respectively). Pollen and honey supplements fed to adults double and triple adult longevity, respectively