Acylsugars of L. pennellii deter feeding and oviposition of the leafminer L. trifolii.

Hawthorne, D.J.,^2^ Shapiro, J. A.^1^, Tingey, W.M.^2^ and Mutschler, M.A.^1^

Departments of Plant Breeding^1^ and Entomology^2^, Cornell University, Ithaca, New York 14853.

Lycopersicon pennellii (Corr.) D'Arcy is a potential source of insect resistance for the cultivated tomato Lycopersicon esculentum (Mill.) (for citations, see reports of Rodriguez et al. and Juvik et al. in this volume of the TGC). Resistance of L. pennellii (LA 716) to the potato aphid, (Macrosiphum euphorbiae (Thomas), is related to the secretion of a viscous mixture of acylsugars from glandular trichomes (type IV) (Goffreda et al. 1989, Steffens & Walters 1991). The objectives of our study were to determine 1) whether L. pennellii (LA 716) and the F1 hybrid L. esculentum X L. pennellii are resistant to the leafminer L. trifolii (Burgess) (Diptera, Agromyzidae), 2) whether the principal mechanism of resistance to this leafminer is the production of acylsugars by type IV glandular trichomes, 3) whether application of purified acylglucoses to leaf tissue confers leafminer resistance to a susceptible commercial tomato cultivar, and 4) a minimum level for the effective concentration of acylglucoses that offers significant resistance to leafminers.

In no-choice feeding and oviposition experiments, both adult feeding and oviposition of the leafminer on L. pennellii and its F1 hybrid with L. esculentum were significantly (84 - 100%) less than that on the cultivated tomato, L. esculentum. Ethanol soluble products of glandular trichomes are implicated in the resistance to this leafminer because: 1) the resistance of L. pennellii and the F1 was greatly reduced following rinsing of foliage with ethanol, and 2) transfer of trichome exudate from leaflets of L. pennellii (LA716) to L. esculentum by appression, resulted in 91% fewer leaf punctures and 80% fewer mines on those leaflets than on leaflets of L. esculentum appressed to other leaflets of L. esculentum. Airbrush application of purified 2,3,4-tri-O-acylglucoses (the principal component of type IV glandular trichome exudate of L. pennellii) to L. esculentum leaflets significantly decreased feeding and oviposition on L. esculentum leaflets by 61-99%. These data confirm that the principal mechanism of resistance to this leafminer by L. pennellii is the secretion of these acylglucoses. Dose response analysis of acylglucoses applied to L. esculentum shows that dosages as low as 10% those found on L. pennellii provide large reductions (91%) in leaf punctures and mines. Thus, the introduction of acylsugar mediated leafminer resistance into L. esculentum from L. pennellii could provide effective control of the pest even if the levels of acylsugars on the leaflet surface are lower than those of L. pennellii in. A detailed report on the work on leafminers has been accepted for publication by Entomol Expl. Appl. and should be published later in 1992.

Literature cited:

Goffreda, J. C., M. A. Mutschler, D. A. Ave, W. M. Tingey and J. C. Steffens 1989. Aphid deterrence by glucose esters in glandular trichome exudate of the wild tomato, Lycopersicon pennellii. J. Chem. Ecol. 15:2135-2147.

Steffens, J. C. and D. S. Walters, 1991. Biochemical aspects of glandular trichome-mediated insect resistance in the Solanaceae. In: P.A. Hedin. (ed), Naturally Occuring Pest Bioregulators. A.C.S. symposium series 449. American Chemical Society, Washington, DC.