Survival strategies of Dalbulus maidis during maize off‐season in Brazil

Abstract

Despite the importance of Dalbulus maidis (DeLong & Wolcott) (Hemiptera: Cicadellidae) as a vector of maize‐stunting pathogens, it is not understood how this leafhopper survives the maize off‐season in regions where overwintering hosts do not occur. We investigated migration and the use of alternate hosts as possible survival mechanisms for D. maidis during maize off‐season in Brazil. Dalbulus maidis populations were monitored with yellow sticky cards for 16–29 months in Anastácio (Mato Grosso do Sul State), in two farms with perennial pastures (Pasture1 and Pasture2), where maize had not been planted for >5 years, in a subsistence farm >20 km distant, where maize was annually planted (spring) (Maize1), and in Piracicaba (São Paulo State), where maize was grown year round (Maize2). RAPD‐PCR analysis of leafhoppers sampled on maize in two plots (Maize1 and Pasture1) at 15–20 and 110–120 days after germination was performed. Dalbulus maidis was trapped in the maize plots of all areas, but not in weedy or woody vegetation adjacent to the plots. Higher numbers were trapped throughout the year in Piracicaba, where maize was continuously grown under irrigation, and in the subsistence farm of Anastácio, where volunteer maize plants were available for long periods in the maize off‐season. In Anastácio farms, some population peaks were recorded in the absence of maize from midwinter to early spring, especially after soil plowing. RAPD‐PCR analysis showed that D. maidis populations sampled were genetically similar. Our data suggest that D. maidis uses a mixed strategy to survive the over‐season period in Brazil, in which part of the population overwinters locally on volunteer maize plants or nearby irrigated maize crops, whereas the other individuals migrate to colonize new maize crops in distant areas or regions. We hypothesize that immigrant D. maidis uses the contrast between plowed and vegetated soil as a visual cue for locating new maize crops.

A few sequence polymorphisms among isolates of Maize bushy stunt phytoplasma associate with organ proliferation symptoms of infected maize plants

“…There are differences in transmission efficiencies of MBSP and AY phytoplasma isolates (Murral et al , 1996; Moya-Raygoza and Nault, 1998), and a dynamic spatio-temporal structure of MBSP isolates in the field is suggested by our observation that divergent MBSP isolates were collected from the same maize field in the same year. Moreover, D. maidis is capable of long-distance migration and can also survive locally, probably on alternative plant hosts, when maize plants are absent (Oliveira et al , 2007, 2013; E. Oliveira et al , 2007; Moya-Raygoza et al , 2007). Further studies are required to assess if the necrosis vs. lateral branching symptoms impact MBSP fitness either directly by increasing phytoplasma titres in maize plants or indirectly via promoting leafhopper attraction, migration and transmission.…”

“…Both the pathogen and the vector are present throughout maize production zones in Central and South America (Triplehorn and Nault, 1985; Oliveira et al , 2013; Van Nieuwenhove et al , 2015) and are thought to have coevolved with maize since its domestication from a teosinte ancestor (Nault, 1980; Nault and DeLong, 1980; Doebley et al , 1997). Maize bushy stunt disease symptoms are characterized by leaf reddening, shortening of internodes, plant height reduction (stunting), lower grain yield and lateral shoot production (Nault, 1980).…”

Seasonal and Vertical Distribution ofDalbulus maidis(Hemiptera: Cicadellidae) in Brazilian Corn Fields

“…This decline was also a result of physiological maturity and consequent senescence of the corn plants, an effect accelerated by environmental conditions. It is likely that the corn leafhoppers present in the field abandoned the area using their well-known migration capabilities to find new corn fields to be colonized (Oliveira CM et al 2013a).…”

“…The corn leafhopper transmits phytopathogens very efficiently (Oliveira E et al 2011) and has a high capability of migration, abandoning senescent corn fields and colonizing newly planted ones (Oliveira CM et al 2013a;Oliveira E et al 2015). Investigating the ecological and epidemiological characteristics of this insect vector are essential steps towards successfully managing it.…”

“…Such knowledge is also supportive of important practices such as defining the most adequate locations to apply insecticides or natural enemies (Fernandes et al 2006). Collection methods based on insect attraction to yellow visual stimuli can be important because they permit a simultaneous investigation of population fluctuations and vertical distribution of an insect (Nault 1990;Ávila & Arce 2008;Oliveira CM et al 2013a). Thus, we conducted a study to assess the seasonal and vertical distribution of D. maidis in corn fields in northeastern Brazil, in addition to describing the effect of yellow trap placement at 2 heights on the capture of this corn leafhopper, thus increasing knowledge about the population dynamics of this pest.…”