Exogenous methyl jasmonate induced cassava defense response and enhanced resistance to Tetranychus urticae

Attraction of the two-spotted spider mite, Tetranychus urticae (Acari: Tetranychidae), to healthy and damaged strawberry plants mediated by volatile cues

Tetranychus urticae Koch (Acari: Tetranychidae), the two-spotted spider mite, is a pest that limits strawberry production in Mexico. Little is known about the interactions that occur between T. urticae and healthy strawberry plants or strawberry plants infested by conspecific spider mites. Therefore, in this study we evaluated the attraction of T. urticae to healthy strawberry plants mediated by volatile organic compounds (VOCs), and to plants damaged by conspecifics mediated by herbivore-induce plant volatiles (HIPVs). First, we conducted dual-choice tests using a Y-tube olfactometer with plants and extracts obtained through dynamic aeration. The volatile composition of the extracts was identified using gas chromatography-mass spectrometry (GC-MS). Once the compounds were identified, we also conducted dual-choice tests with selected synthetic compounds. Tetranychus urticae exhibited greater attraction to both healthy and damaged plants compared to the control (clean air). However, when healthy and damaged plants were offered simultaneously, there was no significant preference observed. Bioassays with extracts obtained by dynamic aeration yielded similar results. The identified compounds were terpenes and aromatic hydrocarbons. We found qualitative and quantitative changes between the VOCs emitted by the healthy plant and the HIPVs from mite-damaged plants. The individual compounds α-pinene (10 ng), pseudocumene (10 ng), and limonene (1 ng) and 10 ng of the blend made of α-pinene + pseudocumene + mesitylene + limonene (5:34:57:4) attracted more T. urticae than the control. However, the binary blend of pseudocumene + limonene (91:9) was more attractive than the other binary or three-compound blends evaluated. These results may contribute to developing strategies for the management of this pest.

Bringing Fundamental Insights of Induced Resistance to Agricultural Management of Herbivore Pests

In response to herbivory, most plant species adjust their chemical and morphological phenotype to acquire induced resistance to the attacking herbivore. Induced resistance may be an optimal defence strategy that allows plants to reduce metabolic costs of resistance in the absence of herbivores, allocate resistance to the most valuable plant tissues and tailor its response to the pattern of attack by multiple herbivore species. Moreover, plasticity in resistance decreases the potential that herbivores adapt to specific plant resistance traits and need to deal with a moving target of variable plant quality. Induced resistance additionally allows plants to provide information to other community members to attract natural enemies of its herbivore attacker or inform related neighbouring plants of pending herbivore attack. Despite the clear evolutionary benefits of induced resistance in plants, crop protection strategies to herbivore pests have not exploited the full potential of induced resistance for agriculture. Here, we present evidence that induced resistance offers strong potential to enhance resistance and resilience of crops to (multi-) herbivore attack. Specifically, induced resistance promotes plant plasticity to cope with multiple herbivore species by plasticity in growth and resistance, maximizes biological control by attracting natural enemies and, enhances associational resistance of the plant stand in favour of yield. Induced resistance may be further harnessed by soil quality, microbial communities and associational resistance offered by crop mixtures. In the transition to more sustainable ecology-based cropping systems that have strongly reduced pesticide and fertilizer input, induced resistance may prove to be an invaluable trait in breeding for crop resilience.