Allelochemicals from essential oil-bearing plants have been categorized as green pesticides because they are biodegradable and predominantly non-toxic to vertebrates. With an aim to reduce the use of synthetic insecticides, they represent one of the most promising approaches for eco-chemical control of insects. Eight compounds were evaluated via topical application against third instar Chilo partellus Swinhoe larvae. Thymol was the most active (lethal dose (LD)50 = 189.7 μg/larva) and methyl eugenol the least (LD50 = 1069.4 μg/larva). The compounds were also tested at sublethal levels, i.e. LD10 and LD30, and there was approximately 15–43% of reduction in growth, which was transitory, and some recovery was observed 6 days post-treatment. Compounds were also used as binary mixtures and tested for synergy, using toxicity and feeding inhibition parameters. The data showed that thymol and α-terpineol synergized the effects of both linalool and 1,8-cineole, but linalool with 1,8-cineole exhibited only an additive effect against C. partellus. Although there is no specific generalization that could be drawn relating to efficacy of binary mixtures, the present findings resulted in several complex mixtures that could be developed and tested as leads for effective control of C. partellus.

Ozone effects on plant species mixtures could depend on the characteristics of the species involved, their mixing ratio, or on environmental conditions. Predicting long-term effects on the dynamics of plant communities requires an understanding of the interactions involved. The present experiment was designed to determine the effects of ozone on grassland species in relation to mixing ratio and soil water content (irrigation) using binary mixtures. The grass Trisetum flavescens was grown in potted replacement-series mixtures with Centaurea jacea (Experiment A) or Trifolium pratense (Experiment B). The plants were exposed to three concentrations of ozone in open-top chambers in two irrigation treatments. Total above-ground dry weight over three growth periods was measured. The competitive ability of T. flavescens was expressed as the competitive ratio (CRT). In Experiment B, total above-ground dry weight was reduced by elevated ozone and by reduced soil moisture, and significant interactions were found for ozone × irrigation and ozone × ratio. In Experiment A these effects were not significant. Under well watered conditions, CRT tended to be reduced by elevated ozone in Experiment A, but increased significantly in Experiment B, indicating the importance of the competing species in modifying the ozone effect on T. flavescens. In both experiments reduced irrigation decreased the magnitude of ozone effects on biomass production, which could be related to observed reductions in specific leaf conductance. The results suggest that under well watered conditions the effect of elevated ozone on the competitive balance between species depends on the species mixture, but that the mixing ratio is less important.