Tropentag, October 6 - 8, 2009 in Hamburg "Biophysical and Socio-economic Frame Conditions for the Sustainable Management of Natural Resources"

Factors Influencing Host Plant Preference of Phyllotreta striolata

¹Humboldt-Universität zu Berlin, Department for Horticultural Sciences, Germany
²AVRDC - The World Vegetable Centre, Entomology Unit, Taiwan

Abstract

The striped flea beetle, Phyllotreta striolata, is a serious pest of crucifer crops in the tropics. This study aimed to elucidate the chemical interaction of this flea beetle species with its host plant to develop attractant-based lures, which may serve as efficient alternatives to chemical control. We focused on glucosinolates, the characteristic secondary metabolites of crucifers, and their hydrolysis products, which are known to be involved in host plant finding and/or acceptance of insect specialists, such as P. striolata. The feeding preference of P. striolata was examined among seven economically important crucifer crops (cabbage, kai-lan, Chinese cabbage, pak-choi, winter rape, leafy mustard, and radish). The leaf glucosinolate content and profile was analysed using high performance liquid chromatography and the total, aliphatic, and indolyl glucosinolate content was correlated with the bioassay data. The corresponding glucosinolate hydrolysis products were analysed with gas chromatography-mass spectrometry. Moreover, the leaf surface, which is the location of initial contact with the potential host plant, was examined using scanning electron microscopy. In multiple choice experiments, radish was the most preferred host plant, followed by leafy mustard, pak-choi, winter rape, and Chinese cabbage. Antixenosis (non-preference) was observed for Brassica oleracea var. capitata (cabbage) and var. alboglabra (kai-lan). The total glucosinolate content in the crops ranged from ~10 µmole/g dry weight in cabbage to ~130 µmole/g dry weight in radish and leafy mustard. Allylisothiocyanate, a volatile GS hydrolysis product and known attractant for P. striolata was detected in leafy mustard ( ~1.5 µmole/g fresh weight) as well as in the non-preferred cabbage (~0.02 µmole/g fresh weight). Although P. striolata prefers to feed on plants with a higher concentration of glucosinolates, especially of aliphatic glucosinolates, the rejection of kai-lan and cabbage could not be explained from the results. Upon examining the leaf surface of the host plants, crystal structures from epicuticular waxes occurred only on cabbage and kai-lan. The waxy surface may hinder P. striolata from attaching to the leaves and block access to nutrients or infochemicals such as glucosinolates; it could be contributing to the insects's antixenosis.

Keywords: Crucifer, glucosinolates, host plant preference, Phyllotreta striolata

Contact Address: Franziska Beran, Humboldt-Universität zu Berlin, Department for Horticultural Sciences, Lentzeallee 55-57, 14195 Berlin, Germany, e-mail: franzi.berangmx.de