Change in abundance of three phytophagous mite species (Acari: Eriophyidae, Tetranychidae) on quackgrass in the presence of choke disease

Relationships between the Pathogen Erysiphe alphitoides, the Phytophagous Mite Schizotetranychus garmani (Acari: Tetranychidae) and the Predatory Mite Euseius finlandicus (Acari: Phytoseiidae) in Oak

Simple Summary

Knowledge about the relationships between plant pathogens, arthropods, and their natural enemies is scarce. We studied the relationships between the plant fungal pathogen, Erysiphe alphitoides, the phytophagous mite Schizotetranychus garmani, and the predatory mite Euseius finlandicus in leaves of pedunculate oak. In June, July and August 2016, in 30 trees located in three forests near Belgrade, Serbia, the presence of E. alphitoides, S. garmani and E. finlandicus was assessed. The occurrence of E. alphitoides was high where the population of S. garmani was high. However, the presence of the leaf pathogen E. alphitoides was not related to the amount of the predatory mite E. finlandicus. The relationships between powdery mildew and the two mite species were stable across time and space, and the presence of one mite was not influenced by the presence of the other mite.

Abstract

Food webs on forest trees include plant pathogens, arthropods, and their natural enemies. To increase the understanding of the impact of a plant pathogen on herbivore-natural enemy interactions, we studied the powdery mildew fungus Erysiphe alphitoides, the phytophagous mite Schizotetranychus garmani, and the predatory and mycophagous mite Euseius finlandicus in pedunculate oak (Quercus robur) leaves. In June, July and August of 2016, we assessed the severity of powdery mildew, mite population density and adult female mite size in 30 trees in three forests near Belgrade, Serbia. In August, the infection severity of E. alphitoides related positively to the population density of S. garmani and negatively to the body size of S. garmani females. Throughout the vegetative season, the infection severity of E. alphitoides related positively to the population density of E. finlandicus but not to its body size. The effect of E. alphitoides on the population density and adult size of S. garmani was not mediated by the population density of E. finlandicus, and vice versa. Interactions were consistent in all forests and varied with the summer month. Our findings indicate that E. alphitoides can influence the average body size and population densities of prey and predatory mites studied, irrespective of predator-prey relationships.

Endophytic entomopathogenic fungi enhance the growth of Phaseolus vulgaris L. (Fabaceae) and negatively affect the development and reproduction of Tetranychus urticae Koch (Acari: Tetranychidae)

Entomopathogenic fungi (EPF) have primarily been applied as an inundative approach to manage pests. However, in recent decade multifunctional role of EPF have been documented which provide multiple benefits to host plants when colonized as an endophyte. In this study five fungal isolates from the genus Beauveria (three), Isaria (one) and Lecanicillium (one) were evaluated for their ability to colonize common bean, Phaseolus vulgaris and to assess their effects in planta on plant growth promotion and possible negative effects on the two-spotted spider mites, Tetranychus urticae. All the tested isolates in this study were able to endophytically colonize root, stem and even leaves of inoculated plants examined at 7 and 14 days post inoculation, indicating the systemic colonization of EPF. Colonized plants showed increased plant heights, fresh shoot and root weights compared to plants without inoculation. Survivorship of T. urticae significantly differed among the treatments with higher survival probability in control plants. Significant reduction in larval development, adult longevity and female fecundity of spider mites were observed when fed on treated plants compared to control plants. The negative effects were found to be carried over the second generation fed on fresh plants. Overall, our results show (i) the positive effects of fungal endophytes on plant growth, (ii) reduction in population growth rate and (iii) negative effects of endophytes on growth and reproduction of spider mites in successive generations. The study presents reports on the endophytic management of plant-feeding mites and highlights the possibility of utilizing entomopathogenic fungal endophytes in the integrated pest management program.