Positive and negative effects of phoretic mites on the reproductive output of an invasive bark beetle

When multiple species coexist upon a single host, their combined effect on the host can be unpredictable. We explored the effect of phoretic mites on the reproductive output of the five-spined bark beetle, Ips grandicollis. Using correlative approaches and experimental manipulation of mite numbers we examined how mite load affected the number, size and condition of bark beetle offspring produced. We found that mites have both negative and positive consequences on different aspects of bark beetle reproduction. Females from which mites were removed were more fecund and produced larger offspring than females with mites, implying a cost of mite loads. However, when mites were present on females, those bearing the highest mite loads produced offspring that were larger and in better condition, indicating a beneficial effect of mites. These data suggest that phoretic interactions between mites and bark beetles differ over the course of the host’s lifespan, with either the mites interacting in different ways with different life stages of the host (parasitic on adult, mutualistic with larvae), and/or the beetles being host to different mite assemblages over their lifetime.

Potential new sources of wheat curl mite resistance in wheat to prevent the spread of yield-reducing pathogens

The wheat curl mite (WCM), Aceria tosichella Keifer (Trombidiformes: Eriophyidae), is a major pest in cropping regions of the world and is recognised as the primary vector of several yield-reducing pathogens, primarily affecting wheat. Management of WCM is complicated due to several aspects of the mite's biology and ecology; however, commercially viable mite resistant wheat varieties may offer practical long-term management options. Unfortunately, mite populations have adapted to previously identified sources of resistance, highlighting the need for further sources of resistance and the value of stacking different resistances to give greater degrees and longevity of control. In this study we assessed the susceptibility of 42 wheat-derived genotypes to mite population growth using a new experimental method that overcomes methodological limitations of previous studies. Experimental wheat lines included a variety of wheat genotypes, related Triticeae species, wheat-alien chromosome amphiploids, and chromosome addition or substitution lines. From these we identify new promising sources of WCM resistance associated with Thinopyrum intermedium, Th. ponticum and Hordeum marinum chromosomes. More specifically we identify group 1J and 5J chromosomes of the L3 and L5 wheat-Th. intermedium addition lines as new sources of resistance that could be exploited to transfer resistance onto homoeologous wheat chromosomes. This study offers new methods for reliable in situ estimations of mite abundance on cereal plants, and new sources of WCM resistance that may assist management of WCM and associated viruses in wheat.