Repellency and oviposition deterrence of wild tomato leaf extracts to spider mites, Tetranychus urticae Koch

Glandular trichomes on the leaves of wild tomato, Lycopersicon hirsutum f. hirsutum Mull, also known as Solanum habrochaites (Solanaceae) synthesize and accumulate high levels of methyl ketones (MKs). The potential of using MKs as alternatives to synthetic acaricides for controlling the twospotted spider mite, Tetranychus urticae Koch, is explored in this study. Plants of L. hirsutum accession LA 407 having high concentrations of MKs were grown from seeds under greenhouse conditions. The main objective of this investigation was to conduct bioassays that are quick and easy to implement, consistent over time (repeatable) with the ability to utilize small amounts of test material for testing repellency and fecundity (number of eggs laid by a female mite) of MKs in pure forms and in LA 407 crude extracts. Four MKs (2-tridecanone, 2-undecanone, 2-dodecanone, 2-pentadecanone) and their mixture were screened for their repellency and ability to alter fecundity of spider mites. All MKs repelled spider mites at the two periods tested. Following spraying of tomato leaf extracts prepared in ethanol (ethanol extracts), average number of eggs laid per female mite on bean leaf discs dropped from 0.8 to 0.3 and from 0.9 to 0.3 at 4 and 24 h after exposure representing 65 and 68% reduction, respectively. However, spraying of tomato leaf extracts prepared in water (water extracts) reduced number of eggs laid per female mite from 1.7 to 0.7 and from 2.6 to 0.9 at 4 and 24 h after exposure representing 60 and 67% reduction, respectively. We concluded that all MKs have repellent and egg laying deterrence activities against spider mites. This investigation suggests that ethanol and water extracts of LA 407 have a potential for repelling female spider mites and reducing their laid eggs which might be explored under field conditions for managing populations of spider mites, which could reduce reliance on synthetic acaricides.