Insects, like all eukaryotes, require sterols for structural and metabolic purposes. However, insects, like all arthropods, cannot make sterols. Cholesterol is the dominant tissue sterol for most insects; insect herbivores produce cholesterol by metabolizing phytosterols, but not always with high efficiency. Many insects grow on a mixed-sterol diet, but this ability varies depending on the types and ratio of dietary sterols. Dietary sterol uptake, transport, and metabolism are regulated by several proteins and processes that are relatively conserved across eukaryotes. Sterol requirements also impact insect ecology and behavior. There is potential to exploit insect sterol requirements to ( a) control insect pests in agricultural systems and ( b) better understand sterol biology, including in humans. We suggest that future studies focus on the genetic mechanism of sterol metabolism and reverse transportation, characterizing sterol distribution and function at the cellular level, the role of bacterial symbionts in sterol metabolism, and interrupting sterol trafficking for pest control.

Spodoptera frugiperda is a significant migratory invasive pest, identified as a serious threat to agricultural production and food security in China. However, to our knowledge, the effects of most host plants on the biological characteristics of S. frugiperda have not been well studied. To develop effective management strategies for S. frugiperda in its new invasive habitat, basic biological and ecological knowledge of this pest are crucial requirements. Here, we examined the effects of six cash crops maize, wheat, soybean, tomato, cotton and Chinese cabbage on the development, survival, fecundity of S. frugiperda by using the age-stage, two-sex life table. The preadult stage, adult preoviposition period and total preoviposition period of S. frugiperda were shortest on maize and wheat but were longest on tomato. Fecundity was greatest on maize and wheat but smallest on tomato. The highest intrinsic rate of increase, finite rate of increase, net reproductive rate and the shortest mean generation time were recorded on maize. This present study showed that S. frugiperda could cause great economic losses to these cash crops, which should attract the attention of agricultural management departments. Our findings provide useful information in predicting population dynamics and understanding the potential damage that could be incurred by S. frugiperda invasion.

The fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith), is a significant invasive pest identified as a serious threat to global agricultural production and food security. However, its ovipositional preference, larval feeding selectivity, and nutritional indices are less studied. Here, we investigated these traits of FAW when fed on maize, wheat, soybean, tomato, cotton, and Chinese cabbage, and analyzed the correlation between its nutritional indices and the nutritional contents of crops. The results showed that the highest number of eggs were laid on maize and the lowest number were laid on tomato. The highest feeding choice rate of third instar larvae was on maize, and the lowest was on Chinese cabbage. The fifth instar larvae showed the highest feeding choice rate on maize, but no significant differences were found among other crop species. The food consumption (FC), the relative growth rate (RGR), and the approximate digestibility (AD) were significantly higher on maize and wheat, while the efficiency of conversion of ingested food (ECI) and the efficiency of conversion of digested food (ECD) were significantly higher when fed on cotton and Chinese cabbage. The FC, the relative consumption rate (RCR), RGR, and AD were significantly and positively correlated with soluble sugar and protein contents of host plants, while the ECI and ECD were significantly and negatively correlated with the soluble sugar content. The present study indicates that FAW may cause potential economic losses to these crops besides maize, and these findings are valuable in managing and controlling this pest.

Low proportion of essential amino acids (EAAs) is one of the barriers for animals to use phloem as a diet. Endosymbionts with EAAs synthesis functions are considered crucial for ameliorating the lack of EAAs in insects’ diets. In this study, we transferred the insects from a cabbage-rearedMyzus persicaepopulation onto 3 new plant species including eggplant, tobacco and spinach. The performance on these plants was evaluated and the dynamics of endosymbionts in relation to this host alternation were recorded. We found that the EAAs ratio in phloem was largely determined by the concentrations of non-essential amino acids and the higher proportion of EAAs seemed to favor the population establishment on new plant species and the growth of primary endosymbionts inside insects, which indicated that nitrogen quality was an important factor for aphids to infest and spread on new plant hosts.