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Climate change is anticipated to lead to an increase in the occurrence and intensity of drought and fluctuations in insect cycles that will challenge modern pasture systems. Feeding by root aphids such as Aploneura lentisci Pass. can be a significant challenge to pastures. These below-ground living aphids are commonly found in New Zealand and Australia, feeding year-round on the roots of graminaceous plants such as perennial ryegrass (Lolium perenne L.). Some strains of the fungal endophyte Epichloë festucae var. lolii in perennial ryegrass can provide protection against root aphids and greater resilience under drought, contributing to higher persistency and growth than endophyte-free plants. However, the interaction between insect pressure and drought is not understood. This study examined the effect of drought on root aphid populations and plant performance in perennial ryegrass plants relative to endophyte status (±) and endophyte strain (AR37, NZCT) in a glasshouse experiment. Plants were cloned across the drought and well-watered treatments, and half of the plants were inoculated with root aphids, whilst half of the plants were treated with insecticide. Endophyte infection with strain NZCT and AR37 reduced root aphid numbers. Aphid populations were significantly higher in drought-stressed than in well-watered plants in both endophyte-infected and endophyte-free treatments. Under drought conditions, root aphid populations were increased 4-fold in NZCT and 8-fold in AR37 and endophyte-free plants in comparison with their well-watered counterparts. Root aphids reduced shoot dry weight by 16% in drought-exposed and 26% in well-watered plants in comparison with their insecticide-treated counterparts whilst reducing root biomass by 49%. Our results suggest that root aphids are likely able to exploit the higher availability of amino acids in the plant sap of drought-exposed plants. This study provides evidence that climate change-mediated impacts of root aphids could reduce production in perennial ryegrass-dominant pastures. However, field trials would be necessary to determine whether this effect is seen in situ, where numerous additional factors will be operating at the same time. [ABSTRACT FROM AUTHOR]

Argentine stem weevil adults (ASW, Listronotus bonariensis) feed on the leaves of agricultural grasses and their larvae mine the pseudostem, causing extensive damage that can result in plant death. Plants emit volatiles that serve as signals to host-searching insects and these odours can be altered by both herbivory and fungal endophyte-infection. This study investigated whether ASW adults utilise olfaction to identify their host plants, perennial ryegrass (Lolium perenne), and if conspecific herbivory or the presence of Epichloë festucae var. lolii fungal endophytes (strain wild-type or AR1) influenced such responses. Results from olfactometer bioassays established that ASW adults were able to utilise their olfactory response to orient towards volatiles released by perennial ryegrass and further, the weevils displayed a preference for plants previously damaged by conspecific weevils. However, there was no evidence that weevils had the ability to distinguish between endophyte-infected and endophyte-free plants using olfaction alone. Using a push–pull extraction technique, thirteen volatile compounds were identified in the blend released by perennial ryegrass. Endophyte and herbivory were found to alter these volatile compounds and quantities emitted by this forage grass. This study suggests that despite observing differences in the plant volatile blend, ASW do not perceive endophyte (wild-type and AR1) using olfaction alone and must rely on other cues, e.g. contact chemoreception or post-ingestional malaise, to detect the presence of a bioactive endophyte in an otherwise acceptable host plant. [ABSTRACT FROM AUTHOR]

The gray field slug, Deroceras reticulatum, is a key pest of seed crops. There is an increasing interest in developing new chemical controls due to limited management options. Essential oils, being non-toxic to humans and exempt from pesticide registration and residue tolerance requirements under US federal law (Sect. 25(b) of the Federal Insecticide, Fungicide, and Rodenticide Act), could be safe and easily implementable alternatives. In this study, the most toxic essential oils to D. reticulatum adults of 13 plant-derived essential oils and one synthetic toxin (caffeine) were determined based on Lethal Concentration 50 values produced in a laboratory Petri dish bioassay. Thyme, spearmint, and pine oil were the most lethal, causing 50% mortality of D. reticulatum at concentrations of 0.148, 0.153, and 0.176% (v/v), respectively. Thyme and spearmint oil were then tested in a greenhouse microcosm experiment and a separate phytotoxicity assessment. In the greenhouse, slugs were added to containers planted with annual ryegrass (Lolium multiflorum) and the containers were sprayed with either 0.5% (v/v) essential oil emulsion, Slug-Fest (industry standard molluscicide), surfactant control at 1% (v/v), or water control. Both oils caused 97.5% mortality of slugs, performing comparably to metaldehyde. Phytotoxic effects were assessed by spraying oils on seedlings and adult plants of two cultivars each of perennial ryegrass (Lolium perenne) and tall fescue (Festuca arundinacea). No definitive signs of phytotoxicity were observed upon visual inspection, and there were no differences in chlorophyll content or biomass between treated and untreated plants. [ABSTRACT FROM AUTHOR]

Essential oils are being investigated as potential herbicides or to provide leads to new environmentally and socially acceptable herbicides. Novel hydroxy and ester derivatives of 1,8-cineole and 1,4-cineole were synthesised, by chemical and biological methods, and have shown pre-emergence herbicidal activity against annual ryegrass and radish. Effects on post-emergence activity of these derivatives, as well as 1,8-cineole, eucalyptus oil and the carboxylic acids from which the esters were derived, against annual ryegrass and radish, are reported here. Results suggest that reduced root and shoot growth observed in pre-emergence herbicidal bioassays were due to post-emergence activity rather than delayed germination. All tested substances had a dose-dependent, post-emergence herbicidal activity against annual ryegrass and radish with many derivatives showing improved activity relative to 1,8-cineole and high-cineole eucalyptus oil. However, results do not support the postulate that cineole esters would be more active than their respective carboxylic acid and the hydroxy cineole. Phytotoxicity of ester derivatives may be due to metabolic cleavage of the esters to the hydroxy cineole and carboxylic acid within the plant. [ABSTRACT FROM AUTHOR]