Comparative toxicity of Deverra scoparia essential oil and blends of its major constituents against Tetranychus urticae Koch

The phytophagous two-spotted spider mite Tetranychus urticae Koch is a ubiquitous species, present worlwide on a large variety of plant families. Since T. urticae resistance spread rapidly, biological control tactics are crucial to manage spider mite populations. In this respect, plant-derived essential oil products are a good alternative as they are, in general, considered as minimum-risk pesticides. In that context, laboratory experiments were conducted to assess the toxicity of essential oil of Deverra scoparia endemic plant to North Africa on females of the two spotted spider mite T. urticae (Koch). Essential oil was distillated from fresh leaves from D. scoparia and was sprayed on groups of adults females. The susceptibility of these females to D. scoparia essential oil was tested. A series of dilutions were used to bracket the dose-response range. Tests proved that female mortality increased with essential oil concentration with DL50 and DL90 values of 1.79 mg/l and 3.16 mg/l, respectively. The analysis of D. scoparia essential oil using GC-MS revealed presence of 10 major constituents: alpha-thujene, alpha-pinene, sabinene, myrcene, 3-carene, ocimene, terpinene-4-ol, pulegone, eugenol and beta-eudesmol. For a comprehensive evaluation of the potential of D. scoparia essential oil as acaricidal, individual blends activity of these constituents were tested against T. urticae female. Toxicity of blends of different components indicated significant differences among the active and inactive components, with the presence of all constituents necessary to have toxicity near to that of whole D. scoparia oil. The results showed that natural oil of D. scoparia and some of its constituents have potential for development as botanical acaricide, at least against T. urticae.