Drought × herbivory induce leaf trichomes in soybean with differential impact on its major herbivore soybean looper Chrysodeixis includens

Trichomes have been well studied as a physical defense against stress. With climate change, stressors like drought and/or herbivory can have exacerbated effects on crop morpho-physiology. However, the interactive effects of such stressors on physical defenses like trichomes and their effects on herbivores is poorly understood. To examine this, soybean plants were exposed to a major herbivore, soybean looper (SBL) (Chrysodeixis includens Walker), under simulated drought conditions to examine the interactive effects of drought and herbivory (D × H) on leaf trichomes. Additionally, SBL growth traits were monitored under different leaf diet concentrations (10% and 20%) and trichome enriched diets (high and low density). Then, a time to feed experiment was conducted to estimate the impacts of trichome on SBL feeding initiation. The results showed that D × H significantly increased trichome density in new leaves compared to H only. However, under 20% leaf diet, SBL experienced a positive larval mass gain, but more caterpillars pupated early under D × H leaf diet leading to early eclosion as well. We also observed that SBL initiated feeding faster on shaved compared to unshaved leaves and the caterpillars that fed on high trichome concentration diet had a higher number of trichomes in their frass. The results demonstrate that trichomes are induced under D × H and may have pre- and post-ingestive effects on SBL. Taken together, the highly inducible nature of trichomes due to abiotic and biotic stressors has the potential to be further explored in defense priming and introgression into resistance breeding programs and sustainable pest management.