BEHAVIORAL DIFFERENCES IN HOST- FINDING AMONG TWO MAIZE DISEASE VECTORS: Dalbulus maidis (CICADELLIDAE) AND Peregrinus maidis (DELPHACIDAE).

JACOBI VANESA GISELA; VIRLA EDUARDO; COLL ARÁOZ MARÍA VICTORIA; JORGE ZAVALA; FERNANDEZ PATRICIA C.

Mendes, R.J

Congreso; 15 th International Auchenorrhyncha Congress and 10 th International Workshop on Leafhoppers and Planthoppers of Economic Importance; 2017

Among the main maize diseases in Argentina there are those that are caused by maize-stunting pathogens transmitted in a persistent propagative way by the leafhopper Dalbulusmaidis and the planthoppers Delphacodes kuscheli and Peregrinus maidis.Dalbulus maidis (DeLong) is considered a serious maize pest throughout most of LatinAmerica, primarily by serving as a vector of Corn Stunt Spiroplasma (CSS), Maize RayadoFino Virus (MRFV) and Maize Bushy Stunt Micoplasm (MBSM). It is a specialistherbivore feeding only on plants of the genus Zea, maize (Zea mays L.) and its wildrelatives, the teosintes (Zea spp.). In Argentina it is present in the NW and NE (Carloni etal. 2013).Although Delphacodes kuscheli is the main vector of Mal de Rio Cuarto Virus (MRCV),the most prejudicial stunting pathogen in Argentina, it has been demonstratedexperimentally that Peregrinus maidis (Ashmead), a planthopper present in the center, NEand NW of Argentina, could also transmit MRCV (Virla et al. 2004), besides being aknown vector of several other diseases. P. maidis is a more polyphagous insect, althoughmost frequently associated with maize, it has been found on Sorghum spp., Panicum spp.,other grasses, and even Citrus (Tesón & Remes Lenicov, 1989).Behavioural differences in host-finding among different maize germplasms have not beenstudied, and may contribute to the pest status of stunting pathogens vectors. In this study,we compared the preferences of a specialist leafhopper D. maidis (Hemiptera: Cicadellidae)and a more generalist planthopper, P. maidis (Delphacidae) on a suite of three maizecultivars, a temperate and a tropical germoplasm and a landrace. Moreover, we analysed thevolatile organic compounds (VOCs) emitted constitutively by the maize plants that couldact as non-contact cues determining host-finding.Materials and methodsTwo corn hybrids, P1780YR (temperate) versus P30B39HR (tropical) and a landraceknown as sweet white maize (SWM) were employed. Maize plants were planted in potswith commercial soil and left in greenhouse conditions until analysis. Insects were obtainedfrom a colony reared in PROIMI.Olfactometer Bioassays: The attractiveness of volatile compounds from V2 maize plantsfrom the three evaluated germplasm on D. maidis and P. maidis females was evaluated inolfactory dual choice tests using a stationary phase olfactometer, with the odor sourcesplaced in opposite directions. The system consisted of a central choice chamber and two opposite side arms connected to glass cages with the odor source plants. The first choice ofeach female was recorded when it trespassed about an inch towards the odor source in theolfactometer arm. Statistical differences in choices made by the females where determinedwith Chi-square goodness-of- fit test (χ 2 ).Volatile Collection and Chemical Analysis: Headspace samples were taken by enclosingintact V2 plants into a 2L glass recipient. Charcoal-filtered air was pushed into the recipientwith an aquarium air pump and then pulled by a suction pump at a constant rate of 0.5 L permin. Air leaving the recipient through an outlet passed through a volatile collection trap (30mg HayeSep Q) where volatiles were collected. After a sampling period of 6 h (between10:00 and 16:00 h), the volatile collection traps were eluted with 150 μl of dichloromethanecontaining 5 ng of dodecane as internal standard. Samples were analysed by GC/MS.ResultsAdults of Dalbulus maidis preferred seedlings with temperate genetic background (75%)instead of tropical background ( 2 = 10.000, P = 0.002). D. maidis was slightly moreattracted, but not significantly, towards SWM (60,8%) over tropical maize ( 2 = 2.174, P =0.140), and did not discriminate between white and temperate maize ( 2 = 0.364, P =0.546).On the other hand, Peregrinus maidis chose seedlings with tropical genetic background(71,4%) over temperate maize ( 2 = 7.714, P = 0.005); and significantly chose SWM(69,5%) over temperate ( 2 = 7.043, P = 0.008). P. maidis did not discriminate betweenSWM and tropical maize ( 2 = 0.857, P = 0.355).All three types of corn differed both qualitatively and quantitatively in their constitutivevolatiles compounds. Temperate corn was correlated with a greater abundance ofmonoterpenes, whereas SWM was positively correlated with aromatic compounds andtropical maize lacked monoterpenes, homoterpenes and salycilates. This results suggest thatboth D. maidis and P. maidis could select their host plants based on the emitted VOCs,even though having opposed comportamental responses.ReferencesCarloni, E., Carpane, P., Paradell, S., Laguna, I. & Gimenez Pecci, M.P. (2013) Presence ofDalbulus maidis (Hemiptera: Cicadellidae) and of Spiroplasma kunkelii in theTemperate Region of Argentina. Journal of Economic Entomology 106, 1574-1581.Tesón, A. & A. M. M. de Remes Lenicov, A.M.M. (1989) Contribución al estudio de losfulgoroideos argentinos IV (Homoptera-Fulgoroidea). Observaciones sobre tresespecies halladas en cultivos de maíz (Zea mays L.). Revista de la SociedadEntomológica Argentina 47, 101-107.Virla, E., Miotti, I., Giménez Pecci, M.P., Carpane, P. & Laguna, G. (2004) Peregrinusmaidis (Hem.: Delphacidae), new experimental vector of the «Mal de Río Cuarto»disease to corn. Biocell, 28(1), 54.