Biochemical and Morphological Mechanisms Underlying the Performance and Preference of Fall Armyworm (Spodoptera frugiperda) on Wheat and Faba Bean Plants

Abstract

Spodoptera frugiperda (J. E. Smith), which attacked China in 2019, remains a significant threat to wheat production. Wheat–faba bean intercropping systems prevent damage caused by wheat aphids; however, the potential role in S. frugiperda control remains unclear. Here, the adaptability and preferences of S. frugiperda to wheat and its common intercropped plant, faba bean, were evaluated to implement an eco-friendly approach for S. frugiperda management. Their adaptability showed that both hosts could support S. frugiperda to complete their life cycle; however, the larvae performed worse on faba bean compared with on wheat. The biochemical analysis revealed that faba bean plants had lower contents of soluble sugars and total proteins but higher levels of phenolics and tannins than in wheat leaves. The gravid S. frugiperda preferred (during the preference assays) to oviposit on wheat rather than on faba bean plants in cage tests. The wheat odor was preferred over the faba bean odor in the Y-tube olfactometer bioassays. The morphological scanning electron microscopy (SEM) showed increased trichome density on wheat leaves. Therefore, the faba bean plants displayed antibiosis on larvae and were repellent to female moths, thus, suggesting that faba bean plants could serve as a push crop to be intercropped with wheat for S. frugiperda control for wheat fields.

Sub-optimal host plants have developmental and thermal fitness costs to the invasive fall armyworm

“…It is highly polyphagous and is an opportunistic feeder, with >350 hosts ( 27 ). Whereas more optimal hosts, e.g., maize, sorghum, and sugarcane, support their entire development (egg to adult) ( 26 , 50 ), suboptimal hosts support larval feeding but are rarely reported to support the entire life cycle ( 21 , 22 , 26 ). Our results here show that survival on suboptimal hosts supports the entire life cycle but comes at ecological costs, e.g., of larval size and increased numbers of instars (prolonged developmental period) ( 26 ; Table S1 ).…”

“…However, in studies that investigated the use of natural host plants, some of the key tropical and subtropical crops such as pearl millet and cowpeas, critical for sub-Saharan African agro-ecosystems, were omitted. Furthermore, previous research did not cover the effects of non-preferred conditions or forms (e.g., drought-stressed forms) of these hosts on the physiological and ecological fitness of associated insect species ( 21 , 22 ). For example, the interactive effects of biotic (e.g., host quality and type of available food or diet) and abiotic stress (thermal responses due to suboptimal diets) have not been specifically investigated.…”