UP KK 03
Manipulation of insect vector behaviour by aster yellows phytoplasma: potential for vector control
University of Pretoria. Faculty of Natural and Agricultural Sciences. Department of Zoology and Entomology
La Grange, R
Phytoplasmas can influence the behaviour of vectors by modifying plant and insect characteristics, for example by altering plant volatiles to lure their insect vectors to infected plants. In addition, sieve tube elements of phytoplasma-infected plants have been reported to contain increased levels of sucrose of up to 1 M which may influence feeding time and potentially the acquisition of phytoplasma by insect vectors.
The objectives of the study were (i) to determine the influence of sucrose on feeding of the vector Mgenia fuscovaria (Stål) (Hemiptera: Cicadellidae), (ii) to identify volatile compounds that manipulate M. fuscovaria and could thus be used in vector management strategies, e.g. traps, to improve disease management, (iii) to determine if the grass feeding leafhopper Aconurella prolixa (Lethierry) (Hemiptera: Cicadellidae) is a vector of aster yellows phytoplasma (AY), and (iv) to continue monitoring of M. fuscovaria in an AY-infected vineyard.
Microtube-feeding assays were carried out to determine the effect of sucrose concentration on adult M. fuscovaria choice. Different sucrose concentrations (0.001, 0.01, 0.1, and 1 M) were tested in dual choice experiments. Field-collected adult M. fuscovaria tended to prefer sucrose-free buffer solution to a sucrose concentration of 1 M, and a 0.1 M sucrose solution to the buffer. No differences were observed between the lower sucrose concentrations (0.01 and 0.001 M) and buffer solution. The trends observed in the current study suggest that M. fuscovaria prefers sucrose concentrations lower than the 1 M recorded from phytoplasma-infected plants. Therefore, high sucrose levels in AY-infected leaves may not lead to increased feeding times.
The antennal responses of adult M. fuscovaria to volatile compounds of AY-infected and AY-free grapevine branches (cv. Colombard, cv. Chenin blanc) were tested with gas-chromatography coupled electroantennography
(GC-EAG). Although some compounds were identified that elicited antennal responses, the responses were very weak, suggesting that the attraction of M. fuscovaria to AY-infected plants may be mainly based on visual cues. Development of management strategies based on the behaviour of M. fuscovaria should focus on visual cues combined with olfactory cues instead of olfactory cues only. Transmission experiments were carried out with A. prolixa collected from the grass Cynodon dactylo (Poaceae) in an AY-infected vineyard. One individual and the corresponding artificial feeding medium tested positive for AY. Aconurella prolixa is a grass-feeding species. Therefore, controlled transmission experiments were carried out with wheat. Eight out of 51 wheat plants exposed to field-collected leafhoppers tested positive for AY. The identification of A. prolixa as a potential vector suggests complex interactions between AY, host plants and the involvement of potentially more than one leafhopper vector species in the pathosystem.
The leafhopper vector M. fuscovaria has been monitored with yellow sticky traps in an AY-infected vineyard in Vredendal since 2009. The population of M. fuscovaria monitored in the field was severely affected by the continued drought. Very few adults were collected between May and December 2017, although there is usually a peak in abundance (numbers) in June/July, suggesting that the risk of spread of AY was low during this period.
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Krüger, K. 2015. Current innovations in insect pest control – Plant volatiles as targets for plant breeding. Paper presented at the 2nd Annual DuPont Plant Breeding Symposium Africa. 29 September, Pretoria, South Africa.
Krüger, K, La Grange, R, Schröder, M L, Ignell, R, Glinnwood, R. 2015. Influence of aster yellows phytoplasma in grapevine on the leafhopper vector Mgenia fuscovaria. Paper presented at the 40th Meeting of the IOBC-WPRS Working Group. Pheromones and Other Semio-Chemicals in Integrated Production: The Good Sense of Scent. 8-13 November, Jerusalem, Israel.
La Grange, M.R, Schröder, M, Glinwood, R, Ignell, R, Krüger, K. 2015. Preference for phytoplasma-infected plants by an insect vector: a visual or olfactory mechanism? Paper presented at the 19th Congress of the Entomological Society of Southern Africa. 12-17 July, Grahamstown, South Africa.
La Grange, M R, Schröder, M L, Ignell, R, Glinwood, R, Bouwer, M, Krüger, K. 2017. The role of olfaction in host plant location of the leafhopper vector of aster yellows phytoplasma in grapevine vector of aster yellows phytoplasma in grapevine. 2017 Paper presented at the Combined Congress of the Entomological and Zoological Societies of Southern Africa. 3-7 July, Pretoria, South Africa.
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La Grange, R, Schröder, M L, Glinwood, R, Ignell, R, Krüger, K. 2017. Leafhopper interactions with host plants – a role for volatile cues? IOBC-WPRS Bulletin, v. 126 (p. 22-26)
La Grange, M R. 2016. Olfactory responses of the leafhopper vector, Mgenia fuscovaria Stål (Hemiptera: Cicadellidae), to volatiles from aster yellows phytoplasma-infected and uninfected grapevine (Vitis vinifera). MSc. Natural and Agricultural Sciences. University of Pretoria, Pretoria.