Lethal and sublethal effects of four essential oils on the egg parasitoids Trissolcus basalis.

The essential oils from leaves of Schinus molle var. areira, Aloysia citriodora, Origanum vulgare and Thymus vulgaris have showed potential as phytoinsecticides against the green stink bug, Nezara viridula. In this work were evaluated their toxicological and behavioral effects on the parasitoid Trissolcus basalis, a biological control agent of this pest insect. Essential oils were obtained via hydrodestillation from fresh leaves. Insecticide activity in T. basalis females was evaluated in direct contact and fumigation bioassays. Behavioral effects were evaluated in olfactometer bioassays. To evaluate the residual toxicity, females of the parasitoids were exposed to oil residues; in these insects, the sublethal effects were evaluated (potential parasitism and survivorship of immature stages). The essential oils from O. vulgare and T. vulgaris proved to be highly selective when used as fumigant and did not change parasitoid behavior. After one week, the residues of these oils were harmless and did not show sublethal effects against T. basalis. According with these results, essential oils have potential applications for the integrated management of N. viridula.

Identification of volatile synomones, induced by Nezara viridula feeding and oviposition on bean spp., that attract the egg parasitoid Trissolcus basalis.

Bean plants (Vicia faba L. and Phaseolus vulgaris L.) damaged by feeding activity of Nezara viridula (L.) (Heteroptera: Pentatomidae), and onto which an egg mass had been laid, produced volatiles that attracted the egg parasitoid Trissolcus basalis (Wollaston) (Hymenoptera: Scelionidae). Extracts of volatiles of broad bean and French bean plants induced by adults of N. viridula as a result of their feeding activity, oviposition activity, and feeding and oviposition activity combined were analyzed by gas chromatography-mass spectrometry (GC-MS), and tested in Y-tube olfactometer bioassays as attractants for T. basalis females. In extracts from undamaged leguminous plants, green-leaf volatiles were absent or scarcely detected, and monoterpenes and sesquiterpenes were present at trace levels. No significant differences were detected in the profiles of volatiles of undamaged plants, and undamaged plants on which bugs were allowed only to lay eggs. In contrast, feeding and oviposition by adults of N. viridula induced in both leguminous plants a significant increase in terpenoids such as linalool, (E)-beta-caryophyllene, (E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene, and (3E)-4,8-dimethyl-1,3,7-nonatriene, which was induced only in French bean plants. Quantitative comparisons revealed increased levels of (E)-beta-caryophyllene in extracts from feeding-damaged plants with N. viridula egg masses compared to feeding-damaged plants without egg masses. In Y-tube olfactometer bioassays, T. basalis females were attracted by extracts of both leguminous plants only when N. viridula adults were allowed to feed and oviposit upon them. Fractionation of extracts of volatiles from broad bean plants with N. viridula feeding damage and egg masses yielded two fractions. but only the fraction containing (E)-beta-caryophyllene was attractive to the egg parasitoid. These findings indicate that N. viridula feeding and oviposition induce leguminous plants to produce blends of volatiles that are characterized by increased amounts of (E)-beta-caryophyllene, and these blends attract female T. basalis. The role of (E)-beta-caryophyllene as a potential synomone for T. basalis is discussed.