Potential new insecticides for the control of western flower thrips (Thysanoptera: Thripidae) on sweet pepper, tomato, and lettuce.

New pesticides are required to maintain effective resistance management strategies for control of western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae). We tested the efficacy of acetamiprid, and thiamethoxam, two neonicotinoids that represent a newer class of insecticides for the control of thrips. We also tested chlorfenapyr, a pyrrol compound, and a lower than registered rate of the biopesticide spinosad. Laboratory bioassays were used to predict the relative efficacy of insecticides against F. occidentalis and to forecast likely field rates. Two doses within the calculated LC99.99 range were used to predict field rates and trial rates of 0.5 g and 1.0 active ingredient (AI)/liter acetamiprid, 0.025 and 0.05 g (AI)/liter chlorfenapyr, 0.3 and 0.6 g (AI)/liter thiamethoxam, and 0.01 g (AI)/ liter spinosad were tested in the greenhouse against pepper, lettuce, and tomato. With the exception of acetamiprid, field trial doses predicted from laboratory bioassay translated to effective field efficacy. All products controlled F. occidentalis at the rates trialed and so have potential to augment current chemical controls. Increasing mortality correlated with increasing acetamiprid concentration in a greenhouse lettuce trial, suggesting that the higher trial rate (1.0 g [AI]/liter) may be required in some lettuce crops. The lower than registered (0.01 g [AI]/liter) rate of spinosad also significantly reduced F. occidentalis numbers and is a viable control option that may be useful in specific integrated pest management programs. The implications of introducing neonicotinoids into existing insecticide resistance management strategies for F. occidentalis are discussed.

Chlorfenapyr resistance in two-spotted spider mite (Acari: Tetranychidae) from Australian cotton.

The responses of Tetranychus urticae Koch from Australian cotton to chlorfenapyr has been monitored since the 1997--1998 growing season. Resistance was first detected in the 2001--2002 season and then increased quickly in both level and proportion of resistant strains detected. In response, the resistance management strategy for chlorfenapyr use in cotton was altered and now recommends a further restriction of use from two to one spray per season. There was no evidence of negative cross-resistance to the pyrethroid bifenthrin, but chlorfenapyr was associated with an undefined negative cross-resistance.

Potentiation of a propargite and fenpyroximate mixture against two-spotted spider mite, Tetranychus urticae (Acari: Tetranychidae).

Using susceptible and resistant reference strains and standard bioassay methods a new miticide product was screened for efficacy and cross-resistance against two-spotted spider mite, Tetranychus urticae Koch. Experimental product NN1 850.0 EW (fenpyroximate and propargite 3:10 ratio) was significantly (P<0.05) more toxic than either compound tested alone (co-toxicity index 1029). Non-overlapping 95% CIs at the LC50 and LC99 level suggest that there is no cross-resistance to NN1 850.0 EW from existing organophosphate and pyrethroid resistance. NN1 850.0 EW is worthy of further development for T. urticae control.

Use of a generalized linear mixed model to reduce excessive heterogeneity in petroleum spray oil bioassay data.

High heterogeneity (variance) is a consistent and significant problem in petroleum spray oil derived bioassay data. It can mask small statistical differences sought by researchers in relative toxicity or potency analysis. To compensate for excessive heterogeneity, researchers often use very large sample sizes to improve statistical accuracy. We present a statistical method of modeling heterogeneity extending the conventional probit model by adding random effects to it. We illustrate this by reanalyzing 26 of our own published experiments. Twelve of these had excessive heterogeneity that was significantly reduced in ten cases by including random replicate effects with or without random slopes. Five were further improved by allowing a nonlinear (spline) response. The result was tighter confidence intervals for the estimates of lethal dose.

First detection of chlorfenapyr (Secure) resistance in two-spotted spider mite (Acari: Tetranychidae) from nectarines in an Australian orchard.

Chlorfenapyr resistance (2.9- and 19.9-fold respectively at LC50 and LC99 level) was detected in Tetranychus urticae Koch causing control failure following a single application of product to nectarines.

The development of bifenthrin resistance in two-spotted spider mite (Acari: Tetranychidae) from Australian cotton.

Bifenthrin (Talstar) was registered at the beginning of the 1993/94 season for control of Helicoverpa spp. and Tetranychus urticae in Australian cotton. Resistance was monitored in T. urticae following registration but despite the implementation of resistance management, resistance evolved in the 1996/97 cotton-growing season after only four seasons use. During the following three seasons resistance increased progressively both in level (from 1.2- to 109-fold at LC50) and abundance (from 20 to 90% strains) and was linked to field control failures. The evolution of resistance has now reduced the reliability of bifenthrin for T. urticae control in Australian cotton. The impact of bifenthrin resistance in T urticae and its continued management in Australian cotton is discussed.