The study was conducted to characterise the underlying resistance mechanisms responsible for high levels of pyrethroid resistance in Frankliniella occidentalis (Pergande) in Australia. Seven commercially available pyrethroids (acrinathrin, alpha-cypermethrin, bifenthrin, deltamethrin, esfenvalerate, permethrin and tau-fluvalinate) were evaluated against seven F. occidentalis strains collected from ornamentals, fruit and vegetables in three states of Australia. A Potter spray tower was used to test for pyrethroid resistance and all field strains were found to be resistant, with resistance ratios ranging from 15-fold deltamethrin to 1300-fold tau-fluvalinate. The two most resistant strains were further tested for detoxification enzymes that could be involved in resistance. Three synergists, piperonyl butoxide (PBO), diethyl maleate (DEM) and profenofos, which, respectively, inhibit the enzymes cytochrome P-450 monooxygenases, glutathione S-transferases and esterases, were used. The synergism data indicate that multiple mechanisms may be involved in pyrethroid resistance in Australian populations of F. occidentalis. Among the three synergists, PBO considerably reduced pyrethroid resistance in the selected strains compared with DEM and profenofos. The practical implication for PBO use to suppress pyrethroid resistance in F. occidentalis is elaborated.

Western flower thrips, Frankliniella occidentalis (Pergande), has developed a high level of resistance to pyrethroid insecticides in Australia. Biochemical examination of those pyrethroid-resistant populations shows esterase activity 2.0-to 6.5-fold higher in six of the seven resistant field populations compared with the susceptible population. This increase in esterase activity in the resistant populations was further supported by native polyacrylamide gel electrophoresis and inhibition studies with the organophosphate insecticide profenofos. The polyacrylamide gel electrophoresis analysis showed differences in the banding pattern and intensity of the esterase isozymes between the pyrethroid-resistant and susceptible F. occidentalis populations. Glutathione S-transferase activity was significantly higher (up to 1.7-fold) in five of the seven resistant field populations when compared with the susceptible populations. Esterases appear to be an important mechanism that contributes to pyrethroid resistance. Glutathione S-transferases may also play a role in pyrethroid resistance in Australian F. occidentalis populations.

As the ban on methyl bromide widens, the need for an effective phytosanitary fumigant alternative grows. Currently available alternatives, phosphine and sulfuryl fluoride, lack efficacy against the pinewood nematode. Ethanedinitrile is a highly efficacious fumigant with chemical properties similar to methyl bromide. Ethanedinitrile was tested against pinewood nematodes in a large-scale field setting with southern yellow pine wood chips at dose rates of 75 and 120 g/m3 for 24 hours. All treatments resulted in complete control of pinewood nematodes whereas a nontreated control confirmed the presence of live nematodes. These preliminary results confirm the efficacy of ethanedinitrile against pinewood nematodes in pine wood chips under field conditions.