Odorant-binding protein CrufOBP1 in Cotesia ruficrus females plays a pivotal role in the detection of Spodoptera frugiperda larvae.

Cotesia ruficrus presents a promising local natural enemy for controlling the invasive fall armyworm Spodoptera frugiperda in China. However, the mechanisms underlying how C. ruficrus locates its target pest remain unclear. In this study, we analyzed the expression patterns of 18 CrufOBPs across different developmental stages of C. ruficrus, and found that CrufOBP1 exhibited consistent and high expression levels in female adults. CrufOBP1 transcript was predominantly localized in sensilla placodea and sensilla trichodea on the antennae. Additionally, we confirmed the binding properties of CrufOBP1 protein to various cuticular compounds of S. frugiperda larvae. Subsequent electroantennogram and behavioral assays revealed that 1-(2-hydroxy-5-methylphenyl)-ethanone attracted female C. ruficrus, consequently increased the parasitism rate. However, upon silencing CrufOBP1, females exhibited reduced attraction towards 1-(2-hydroxy-5-methylphenyl)-ethanone, indicating the crucial role of CrufOBP1 in the chemoreception of C. ruficrus. These findings shed light on the kairomone-based mechanism employed by C. ruficrus to locate S. frugiperda larvae and hold a promise for the development of environmentally friendly pest management strategies.

Comparative studies of ovipositional preference, larval feeding selectivity, and nutritional indices of Spodoptera frugiperda (Lepidoptera: Noctuidae) on 6 crops.

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.

Identification and expression analysis of chemosensory receptor genes in an aphid endoparasitoid Aphidius gifuensis.

Olfaction and gustation play critical roles during the host-location search process of insects. Several chemosensory receptor genes are thought to be involved in providing specificity to the olfactory sensory neuron responses. The aphid endoparasitoid, Aphidius gifuensis, has been used as a biological control agent against a variety of aphid species; this parasitoid is able to detect its target host(s) effectively during the parasitic process. To understand the mechanism of host detection in A. gifuensis, we assembled specific antennal transcriptomes of each sex through next generation sequencing technology to identify the major chemosensory receptor genes. Using a bioinformatics screen, we identified 100 olfactory receptors candidates (62 odorant receptors, 15 gustatory receptors, and 23 ionotropic receptors) from the sex-specific antennal transcriptome. In addition, combining with the demonstrated functions of chemosensory genes in other insects, the sex-, tissue-, and host-specific expression profile of chemosensory genes potentially revealed the candidate physiological functions. The identification and expression profile of chemosensory receptor genes in A. gifuensis provide valuable information for understanding and investigating the intraspecific or interspecific chemical communications in the solitary parasitic wasps.