NEW PUBLICATION | The influence of host adaptation on crop rotations in managing the redlegged earth mite

Words and photo: Xuan Cheng

This research has been published in the Journal of Economic Entomology

The redlegged earth mite, Halotydeus destructor (Tucker) (Trombidiformes: Penthaleidae) is a polyphagous economic pest in Australia, attacking a broad range of host plants in broadacre farming systems¹. Although applications of pesticides are currently the main method in managing earth mites, resistance against pyrethroid and organophosphate chemicals has been found in some populations of H. destructor^2–4. In order to postpone the evolution of pesticides resistance, it is essential to develop alternative control practices, such as crop rotations.

Host plant preferences between different species of earth mites (e.g. H. destructor and Penthaleus spp.) have been evaluated in previous studies while results were inconsistent. A previous study suggested that H. destructor had a poor survival and reproduction in wheat and oats⁵, while another study showed that H. destructor survived and reproduced well on these plants⁶. Interestingly, mites in the former and latter studies were collected from habitats dominated by clovers and thick-blade grasses, respectively. Clovers belonged to the Fabaceae family, while thick-blade grasses, wheat and oats all belong to the Poaceae family. Therefore, mites in the former study experienced a shift of host species from different families, while mites in the latter study had a shift to host species of the same family.

Many studies show that polyphagous arthropod species can evolve into genetically-based host races to adapt to different defense systems of host plants^7–12. However, genetic studies suggest that H. destructor isn’t subdivided into either host races or geographical races, rather, represents a single population in in Australia^13–15. Hence our study aims to investigate whether host adaptation without causes performance trade-offs on H. destructor even without genetic differentiated races. Adult mites were collected in the same suburb from grasses, legumes and broad-leaf weeds, which belonged to Poaceae, Fabaceae and Asteraceae families, respectively. Then, each mite origin was introduced and reared in microcosms with either grasses, legumes or broad-leaf weeds in order to investigate whether mite performance was impacted by the interaction between the original and introduced host plants.

Our results showed a significant effect of the interaction on the survival and net reproductive output of the parental generation, as well as offspring development and feeding damage. In general, performances were poorer if the original plant type differed to the introduced plant type in microcosms, even though these plants have been reported as suitable hosts. These findings indicate that host adaptation harboured fitness costs which are potentially useful to suppress the population size of H. destructor in crop rotations.

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