Utilizing associational resistance for biocontrol: impacted by temperature, supported by indirect defence

Abstract

BackgroundAssociational herbivore resistance is potentiated by neighbouring heterogenic plant species that impact a focal plant’s attraction to herbivores or the damage that they cause. One mechanism to confer associational resistance is believed to be exposure to neighbour-emitted volatiles, the receivers of which range from intra- and interspecific neighbour plants to higher-trophic-level insects. In previous studies the passive adsorption of neighbour-emitted semivolatiles has been reported, but little is known regarding the mechanisms and ecological consequences on the receiver plant and its associated biota. To utilize volatile-based associational resistance for agricultural applications, it is imperative to know its effectiveness under varying diurnal temperatures and whether herbivore natural enemies, providing biological control, are impacted. Mimicking varying diurnal temperatures in a laboratory set-up, we assessed how the tritrophic model system Brassica oleracea var. italica (broccoli)–Plutella xylostella (crucifer specialist herbivore)–Cotesia vestalis (endoparasitoid of P. xylostella) is influenced by exposure to the natural semivolatile emitter plant Rhododendron tomentosum Harmaja.ResultsRhododendron tomentosum-exposed B. oleracea was less susceptible to P. xylostella oviposition at both night-time (12°C) and day-time (22°C) temperatures and less favoured and damaged by P. xylostella larvae at 12°C. Exposure did not interfere with indirect defence, i.e. attraction of the natural enemy C. vestalis on host-damaged, R. tomentosum-exposed B. oleracea under 22°C, while there was a reduction in attraction (marginal preference towards host-damaged B. oleracea) under 12°C.ConclusionsThe ability of R. tomentosum exposure to render associational resistance against an agriculturally important Brassica herbivore P. xylostella without severely compromising the specialist parasitoid C. vestalis host location encourages further studies on the potential of using this naturally abundant plant for biocontrol. The generality of our finding on temperature as a potential regulating mechanism for the efficacy of semivolatile emitter-based associational resistance towards specialist pest larval damage should be further studied in natural and agricultural associations. Our study emphasizes the need to develop techniques to compare volatiles at the leaf versus air interface and associate their appearance and ecological role with times of activity and level of specialisation of herbivores and their natural enemies.

Who is my neighbor? Volatile cues in plant interactions

“…Apart from active response to VOCs, plants like Betula spp. and broccoli can adsorb ledene, ledol, and palustrol produced by Rhododendron tomentosum and then re-release, making them less attractive to herbivore insects 34,35 (Figure 1(3)).…”

Understorey Rhododendron tomentosum and Leaf Trichome Density Affect Mountain Birch VOC Emissions in the Subarctic

“…RT-specific compounds have been recovered from the VOC emissions of neighbouring plants in boreal ecosystems and laboratory experiments 14,16 . The adsorption and re-release of RT sesquiterpenes by neighbouring plants has been shown to be dependent on temperature 16 .…”

Métodos alternativos para controle de insetos praga em sementes

“…Para as temperaturas, em linhas gerais, gradações acima de 50 °C ou a menos de 5 °C podem matar ou conduzir o inseto a um estado de hibernação ou de estivação permanente, porém as faixas de controle apresentam grandes variações. No tratamento térmico, as sementes podem ser acondicionadas em local com temperatura controlada ou imersas em água quente ou gelada, resultando na morte dos insetos-praga presentes nas sementes (Wermelinger & Ferreira, 2013;Himanen et al, 2015).…”