Survival relative to new and ancestral host plants, phytoplasma infection, and genetic constitution in host races of a polyphagous insect disease vector

Abstract

Dissemination of vectorborne diseases depends strongly on the vector's host range and the pathogen's reservoir range. Because vectors interact with pathogens, the direction and strength of a vector's host shift is vital for understanding epidemiology and is embedded in the framework of ecological specialization. This study investigates survival in host-race evolution of a polyphagous insect disease vector, Hyalesthes obsoletus, whether survival is related to the direction of the host shift (from field bindweed to stinging nettle), the interaction with plant-specific strains of obligate vectored pathogens/symbionts (stolbur phytoplasma), and whether survival is related to genetic differentiation between the host races. We used a twice repeated, identical nested experimental design to study survival of the vector on alternative hosts and relative to infection status. Survival was tested with Kaplan–Meier analyses, while genetic differentiation between vector populations was quantified with microsatellite allele frequencies. We found significant direct effects of host plant (reduced survival on wrong hosts) and sex (males survive longer than females) in both host races and relative effects of host (nettle animals more affected than bindweed animals) and sex (males more affected than females). Survival of bindweed animals was significantly higher on symptomatic than nonsymptomatic field bindweed, but in the second experiment only. Infection potentially had a positive effect on survival in nettle animals but due to low infection rates the results remain suggestive. Genetic differentiation was not related to survival. Greater negative plant-transfer effect but no negative effect of stolbur in the derived host race suggests preadaptation to the new pathogen/symbiont strain before strong diversifying selection during the specialization process. Physiological maladaptation or failure to accept the ancestral plant will have similar consequences, namely positive assortative mating within host races and a reduction in the likelihood of oviposition on the alternative plant and thus the acquisition of alternative stolbur strains.

Phytoplasma Infection of Cranberries Benefits Non-vector Phytophagous Insects

“…Faster growth on phytoplasma-infected plants could provide a fitness advantage as the insects are then not exposed as long to predators and entomopathogens. Previous studies on phytoplasma infection have reported positive (Sugio et al, 2011a;Maixner et al, 2014), negative (Mayer et al, 2011), and neutral effects (Vega et al, 1995) on the performance of insect vectors. There are, however, fewer data on the impact of plant bacterial infections on nonvector species.…”

“…Phytoplasma infection has also been shown to increase levels of plant secondary metabolites, including phenolic compounds and hydrogen peroxide (Junqueira et al, 2004;Musetti et al, 2004;Musetti, 2009). Previous work has shown that these changes in the phytochemistry of phytoplasma-infected plants can influence the behavior of insect vectors (e.g., leafhoppers and psyllids) (Weintraub and Beanland, 2006;Mayer et al, 2008aMayer et al, ,b, 2011Kaul et al, 2009;Maixner et al, 2014). For example, Beanland et al (2000) showed that aster leafhoppers, Macrosteles quadrilineatus Forbes, live longer and have higher fecundity on asters [Callistephus chinensis (L.) Nees] infected by the aster yellows phytoplasma than on uninfected plants.…”

Widespread plant specialization in the polyphagous planthopper Hyalesthes obsoletus (Cixiidae), a major vector of stolbur phytoplasma: Evidence of cryptic speciation

“…H . obsoletus populations affiliated with these plants are well studied in central Europe [ 14 , 25 , 28 ], especially along the northernmost border of the species distribution range [ 7 , 15 , 29 ]. Recent research has also confirmed these associations and its epidemiological importance in southeastern Europe [ 13 , 30 ].…”

Invasive mutualisms between a plant pathogen and insect vectors in the Middle East and Brazil

“…Hence, epidemiology of a pathogen like ‘ Ca . Phytoplasma aurantifolia’ is intimately associated with the evolution of the insect–plant interactions [27,52]. When generalist pathogens are spread by polyphagous vectors, the number and diversity of interactions between pathogen, host and alternative hosts are increased [49].…”