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Abstract
Abamectin has been widely used as an insecticide/acaricide for more than 30 years because of its superior bioactivity. Recently, an interesting phenomenon was identified in the carmine spider mite, Tetranychus cinnabarinus, an important pest in agriculture. The gamma aminobutyric acid (GABA) contents in a laboratory abamectin resistant strain of T. cinnabarinus (AbR) were significantly increased. Decreases in activity and mRNA expression of GABA transaminase (GABA-T) were responsible for GABA accumulation in AbR mites. To clarify the mechanism of GABA accumulation mediated abamectin resistance, three artificial approaches were conducted to increase GABA contents in susceptible mites, including feeding of vigabatrin (a specific inhibitor of GABA-T), feeding of exogenous GABA, and inhibition of GABA-T gene expression. The results showed that susceptible mites developed resistance to abamectin when the GABA contents were artificially increased. We also observed that the mites with higher GABA contents moved more slowly, which is consistent with the fact that GABA is an inhibitory neurotransmitter in arthropods. Subsequently, functional response assays revealed that predation rates of predatory mites on GABA accumulated abamectin-resistant mites were much higher than control groups. The tolerance to abamectin, slow crawling speed, and vulnerability to predators were all resulted from GABA accumulation. This relationship between GABA and predation was also confirmed in a field-collected population. Our finding indicates that predatory mites might be used as a tool for biological control to circumvent the development of abamectin resistance in mites.
Highlights
Spider mites have been one of the most polyphagous arthropods on this planet
The quantitative real time PCR results showed that the expression of glutamate decarboxylase (GAD) (GADTC1 and GADTC2) genes had no significant difference among susceptible (SS), fenpropathrin-resistant (FeR, used as extra control) and abamectin-resistant strains (AbR) (Figure 1A)
As the two most important enzymes in the GABAergic neurons, GAD is responsible for synthesis of gamma aminobutyric acid (GABA) while GABA transaminase (GABA-T) can metabolize GABA into succinic semialdehyde (SSA)
Summary
Spider mites have been one of the most polyphagous arthropods on this planet. They feed on more than 1,100 different plants in the field or in green houses (Grbicet al., 2011). The control of spider mites has been performed almost exclusively with the application of acaricides (Watanabe et al, 1994). An alternative method for the management of spider mites is biological control with predatory mites, which are considered effective natural enemies of phytophagous mites (Helle and Sabelis, 1985). The use of acaricides and predatory mites is mutually exclusive in most cases due to the fact that most acaricides are lack of selectivity between phytophagous and predatory mites
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