Abstract
How herbivorous insects adapt to host plants is a key question in ecological and evolutionary biology. The fall armyworm, (FAW) Spodoptera frugiperda (J.E. Smith), although polyphagous and a major pest on various crops, has been reported to have a rice and corn (maize) feeding strain in its native range in the Americas. The species is highly invasive and has recently established in China. We compared behavioral changes in larvae and adults of a corn population (Corn) when selected on rice (Rice) and the molecular basis of these adaptational changes in midgut and antennae based on a comparative transcriptome analysis. Larvae of S. frugiperda reared on rice plants continuously for 20 generations exhibited strong feeding preference for with higher larval performance and pupal weight on rice than on maize plants. Similarly, females from the rice selected population laid significantly more eggs on rice as compared to females from maize population. The most highly expressed DEGs were shown in the midgut of Rice vs. Corn. A total of 6430 DEGs were identified between the populations mostly in genes related to digestion and detoxification. These results suggest that potential adaptations for feeding on rice crops, may contribute to the current rapid spread of fall armyworm on rice crops in China and potentially elsewhere. Consistently, highly expressed DEGs were also shown in antennae; a total of 5125 differentially expressed genes (DEGs) s were identified related to the expansions of major chemosensory genes family in Rice compared to the Corn feeding population. These results not only provide valuable insight into the molecular mechanisms in host plants adaptation of S. frugiperda but may provide new gene targets for the management of this pest.
Highlights
How plant-feeding insects adapt to new hosts is a key process in their diversification.For phytophagous insects, the process of selecting a host plant is complex and is the result of millions of years of coevolution between plants and animals [1]
First instar larvae of fall armyworm reared on rice plants (Rice-pop) continuously for 20 generations showed a feeding preference toward the alternate host plant as compared to corn (Figure 3A) with the change occurring after 6 generations
First instar larvae of fall armyworm maintained on the primary host plant (Corn-pop) showed a feeding preference toward corn (Figure 3B)
Summary
How plant-feeding insects adapt to new hosts is a key process in their diversification.For phytophagous insects, the process of selecting a host plant is complex and is the result of millions of years of coevolution between plants and animals [1]. How plant-feeding insects adapt to new hosts is a key process in their diversification. Occasional expansion of the host range, as well as the direct role of plant related adaptation leading to effective reproductive isolation between host-specialized populations, are increasingly recognized as factors in the diversification of herbivores [4,5,6,7]. Little is known about the evolutionary processes leading to such host range expansions, since the genetic basis of host plant adaptation mechanisms is not well understood. Molecular based studies of the mechanisms involved in adaptation to host plants have emphasized the importance of key genes relating to sensing, digestion and detoxification [15]. Studies focused on insect olfactory plasticity and modulation mechanisms in the central nervous system (CNS) [20], while recent studies have shown modulation at the olfactory receptors (ORs) within the olfactory neurons (OSNs) on antennae as a function of odor exposure [21,22,23]
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