Maize Bushy Stunt Phytoplasma Favors Its Spread by Changing Host Preference of the Insect Vector.

Abstract

Simple SummaryPhytopathogenic bacteria such as phytoplasmas induce physiological changes in their host plants that may modulate the behavior of an insect vector in favor of their own spread. In this study we investigate changes in the host selection behavior of the leafhopper vector, Dalbulus maidis (DeLong and Wolcott), in choice tests between healthy vs. maize bushy stunt phytoplasma (MBSP)-infected maize leaves (Zea mays L.), for insects previously exposed to infected plants (named “bacteriliferous”) or not (naive). The results showed that males and naive females of D. maids did not distinguish the treatments when infected leaves were still asymptomatic, whereas bacteriliferous females prefer to settle on healthy leaves, a behavior that favors pathogen inoculation and primary spread at early crop stages. During the symptomatic phase of maize infection, naive males and females were initially attracted to infected leaves, favoring pathogen acquisition; interestingly, the females tend to move towards healthy leaves a few hours later, a behavioral shift that promotes secondary spread. Overall, this study presents evidences that MBSP optimizes its spread in maize crops by influencing the host selection behavior of the leafhopper vector.Plant pathogenic bacteria may influence vector behavior by inducing physiological changes in host plants, with implications for their spread. Here, we studied the effects of maize bushy stunt phytoplasma (MBSP) on the host selection behavior of the leafhopper vector, Dalbulus maidis (DeLong and Wolcott). Choice assays contrasting leaves of healthy (mock-inoculated) vs. infected maize (Zea mays L.) were conducted during the asymptomatic and symptomatic phases of plant infection, with leafhopper males or females previously exposed to infected plants (bacteriliferous insects) or not. In each assay, 40 adults were released in choice arenas where only the leaves of two plants from each treatment were offered and visible, and the insects landed on the leaves were counted 1, 2, 3, 5, 7, 9, 11 and 23 h after release. During the asymptomatic phase of plant infection, an effect was observed only on bacteriliferous females, who preferred leaves of healthy plants 5 h after release or later. The symptomatic phase triggered a pull–push effect on non-bacteriliferous females, who were first attracted to symptomatic leaves but hours later moved to healthy leaves. Non-bacteriliferous males initially preferred symptomatic leaves (up to 5 h after release) and later became equally distributed between treatments. Bacteriliferous males and females initially did not discriminate between healthy and symptomatic leaves, but only the females tended to move to healthy leaves 9 h after release. Oviposition was drastically reduced on symptomatic leaves. The changes in vector behavior induced by MBSP favor its primary spread, since bacteriliferous females prefer healthy leaves at early (asymptomatic) stages of the crop. At later stages, secondary spread may be favored because non-bacteriliferous females are initially attracted to infected (symptomatic) leaves, allowing pathogen acquisition and subsequent transmission as they move to healthy plants.