Impact of physical characteristics of some mineral and plant oils on efficacy against selected pests

Mineral oils have been historically favoured over plant oils for insect pest control in horticultural crops because of their greater efficacy. Recently the increased pressure for environmentally sustainable pest management strategies has renewed interest in the use of plant oils and also in the reasons for differences in efficacy between plant and mineral oils. Efficacy of canola and mineral oils were compared for two modes of action: asphyxia in control of Saissetia oleae on olives and as an oviposition deterrent in control of Phyllocnistis citrella on lemons. On olives both canola and mineral oil treatments significantly reduced the number of black scale in comparison to the control but mineral oil reduced the number of black scale significantly more than canola oil. When oils were applied to lemons as a preventative spray, concentrations of canola oil above 0.5% significantly reduced the number of P. citrella mines per leaf compared to the control and there were no significant differences between any concentration above 0.5% canola oil and 0.5% mineral oil. Canola oil applied at a concentration of 0.5% was significantly less effective than mineral oil applied at the same concentration. Efficacy of canola oil was found to be lower than that of mineral oil in all experiments, but the higher efficacy of mineral oil was more pronounced in suffocation of S. oleae than in deterrence of P. citrella oviposition. Our results indicate that even though canola oil has very different molecular structures than mineral oils the resulting physical characteristics of canola oil, primarily high boiling point and viscosity, may contribute to their lower efficacy against arthropod pests. However, low phytotoxicity of canola oil indicates that the chemical structure of molecules contained in canola oil had much more influence on processes on the plant surface than the physical characteristics of the oil.     

Antarctic desert soil bacteria exhibit high novel natural product potential,evaluated through long-read genome sequencing and comparative genomics

Actinobacteria and Proteobacteria are important producers of bioactive natural products (NP), and these phyla dominate in the arid soils of Antarctica, where metabolic adaptations influence survival under harsh conditions. Biosynthetic gene clusters (BGCs) which encode NPs, are typically long and repetitious high G + C regions difficult to sequence with short-read technologies. We sequenced 17 Antarctic soil bacteria from multi-genome libraries, employing the long-read PacBio platform, to optimize capture of BGCs and to facilitate a comprehensive analysis of their NP capacity. We report 13 complete bacterial genomes of high quality and contiguity, representing 10 different cold-adapted genera including novel species. Antarctic BGCs exhibited low similarity to known compound BGCs (av. 31%), with an abundance of terpene, non-ribosomal peptide and polyketide-encoding clusters. Comparative genome analysis was used to map BGC variation between closely related strains from geographically distant environments. Results showed the greatest biosynthetic differences to be in a psychrotolerant Streptomyces strain, as well as a rare Actinobacteria genus, Kribbella, while two other Streptomyces spp. were surprisingly similar to known genomes. Streptomyces and Kribbella BGCs were predicted to encode antitumour, antifungal, antibacterial and biosurfactant-like compounds, and the synthesis of NPs with antibacterial, antifungal and surfactant properties was confirmed through bioactivity assays.     

Integrated pest management of two-spotted mite Tetranychus urticae on greenhouse roses using petroleum spray oil and the predatory mite Phytoseiulus persimilis

From 1995 to 1999, four experiments were conducted on greenhouse roses to assess the effectiveness of the nC24 petroleum spray oil (PSO), D-C-Tron Plus, against two-spotted mite, Tetranychus urticae Koch (Acarina: Tetranychidae), and to determine how the oil could be most efficiently and effectively used in combination with the predatory mite Phytoseiulus persimilis Athias-Henriot (Acarina: Phytoseiidae) in an integrated pest management program. The results showed that 0.5% PSO applied fortnightly to roses gave excellent protection from T. urticae infestation when the mite population was not already established. However, PSO applied after roses were infested with T. urticae above the economic threshold only stabilised populations without reducing them below that threshold. Populations of P. persimilis in the upper and lower canopies were unchanged after two sprays of PSO at 7-day intervals, and application of PSO to the upper canopy was as effective in controlling T. urticae in the presence of P. persimilis as spraying the entire plant. Combining PSO with P. persimilis gave better control of T. urticae than using P. persimilis alone. The most cost-effective use of PSO in the presence of P. persimilis is, therefore, to apply spray only to the upper canopy. This will not affect control of powdery mildew with PSO. Comparison of a control program for T. urticae based on the monitored use of synthetic miticides with that based on calendar application of PSO revealed that both gave equally effective control. The benefits of combining PSO and P. persimilis in an integrated pest management program for T. urticae on roses over a program based on synthetic fungicides are discussed.