The effects of drought and herbivory on plant–herbivore interactions across 16 soybean genotypes in a field experiment

Abstract

As the Earth's climate continues to change, drought and insect population outbreaks are predicted to increase in many parts of the world. It is therefore important to understand how changes in such abiotic and biotic stressors might impact agroecosystems. The plant stress hypothesis predicts that, owing to physiological and biochemical changes, plants experiencing drought will be more susceptible to insect herbivory, which could have synergistic negative effects on plant performance. By contrast, the plant vigor hypothesis predicts that insects will preferentially feed on fast‐growing vigorous plants. These hypotheses were tested in a field experiment using 16 soybean (Glycine max (L.) Merr.) genotypes to determine: (i) the combined effects of drought and herbivory on plant performance; (ii) the impact of drought on soybean resistance to herbivores; and (iii) how genetically variable phenotypic traits in soybean correlate with these responses. It was found that drought had a greater effect on soybean performance than herbivory, and drought and herbivory did not interact to impact on any measure of plant performance. Drought caused decreased insect herbivory on average, suggesting that the plant vigor hypothesis is consistent with the effects of drought stress on soybean resistance to leaf‐chewing insect herbivores. This conclusion is further supported by genotypic correlations which show that plant growth rate is positively correlated with the amount of herbivory plants received. These results suggest that, although the effects of climate‐associated changes in drought and herbivory will have negative effects on soybean, these potential effects are quantifiable with simple experiments and can be mitigated through continued breeding of varieties that are tolerant and resistant to these abiotic and biotic stressors.

Plant water stress and previous herbivore damage affect insect performance

“…). Recent studies have found similar results, where water stress had negative effects on plant quality and insect preference or performance (Grinnan et al ., ; Lenhart et al ., ). However, comparing among studies can be challenging because changes in drought duration and intensity can produce negative, positive, or neutral effects of water stress on insect performance (Huberty & Denno, ; Sconiers & Eubanks, ) and the direction may depend on the feeding guild or diet breadth of the herbivore (Huberty & Denno, ; Mody et al ., ).…”

“…Water stress to host plants can have substantial effects on insect performance through changes in plant quality and resistance traits (Chaves et al, 2003;Huberty & Denno, 2004;Grinnan et al, 2013). However, the combined effects of water stress and previous herbivory is often overlooked in studies that examine the effect of water stress on insect performance.…”

Evaluation of Different Integrated Pest Management Modules to Control Helicoverpa for Adaptation to Climate Change

“…Yadav et al (2006) also reported resistant genotypes of chickpea both against H. armigera and drought. Similarly, significant interaction was found between drought and genotypes of soybean for herbivores (Helicoverpa zea and Spodoptera exigua) (Grinnan et al, 2013). Mao et al (2004) also concluded that two genotypes of sweet potato had different response for sweet potato weevil feeding as well as its oviposition under drought condition.…”

The plant vigor hypothesis applies to a holoparasitic plant on a drought-stressed host

“…Many climate change models predict increased variability in precipitation and regional droughts (Dore 2005;IPCC 2007). While the impact of drought on plantherbivore systems has received considerable attention (e.g., Mody et al 2009;Johnson et al 2011;Grinnan et al 2013), less is known about drought effects on parasitic plants as consumers. Similar to insects, holoparasites can be potent pests (Dawson et al 1994;Sandler 2001;Parker 2010) and have also been considered as agents of biocontrol (Shen et al, 2005;Yu et al 2009Yu et al , 2011.…”