Improved Overwintering Ability in Dalbulus maidis (Homoptera: Cicadellidae) Vectors Infected with Spiroplasma kunkelii (Mycoplasmatales: Spiroplasmataceae)

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Abstract
Available evidence suggests that Dalbulus maidis (DeLong & Wolcott), the major vector of the corn stunt spiroplasma, Spiro plasma kunkelii, overwinters as an adult and has no breeding hosts other than the Zea species (maize and teosintes). Over the dry season, these breeding hosts are often absent, and, although feeding hosts may be available in some habitats, the vector may migrate mid-winter, or both, we argue that D. maidis can spend part or all of the dry and often cold Mexican winter feeding only sporadically, if at all. Because the corn stunt spiroplasma (CSS) apparently overwinters in D. maidis, we investigated its effect on the ability of D. maidis to survive these winter conditions (low temperatures and loss of host plants). We used two types of tests: exposing leafhoppers to either −5°C over 24 h or to less severe low temperatures (10 to 20°C) and starvation over several months. We used leafhoppers reared under fall conditions, previously shown to be more cold hardy, and varied food and water sources to simulate loss of host plants. We compared survival of males and females from laboratory colonies established from three field populations in Mexico. Our results do not support previous findings that CSS infection protects D. maidis from below zero temperatures. However, CSS improved survival at 10 to 20°C when D. maidis was provided only moist sand or maintained on oats (a feeding host), and preferentially benefitted females; for example, over all treatments, survival of infected individuals was 1.1 times that of un infected leafhoppers, but on moist sand, survival of CSS infected females averaged 2.2 times that of uninfected females. We conclude that, under certain conditions, CSS infection can benefit its vector and may play an important role in D. maidis overwintering strategies.

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