Nutritional quality regulates postnatal wing morph in pea aphids.

Aphids can produce winged or wingless offspring in response to environmental changes. Host nutrition is one of the extensively studied environmental factors influencing the plasticity of wing morphs of aphids. In this study, we found that the pea aphid, Acyrthosiphon pisum, produced a low proportion of winged offspring when fed on plants, but a significantly higher proportion on the artificial diet. Interestingly, when newly born nymphs were transferred back to the artificial diet after feeding on plants for six hours or longer, most nymphs became wingless. These results suggest that the wing morph state of pea aphids can change postnatally, potentially determined by the nutritional quality of their food. Furthermore, aphids feeding on the artificial diet exhibited higher levels of glucose and stronger insulin signaling activity compared with aphids on plants. Conversely, the amino acid levels were lower, and TOR signaling was weaker in aphids fed on the artificial diet. Insulin and the target of rapamycin (TOR) are the primary nutrient-sensing signaling pathways involved in controlling organism growth and have been implicated in regulating aphid wing morph plasticity. We tested whether these nutrient responsive pathways were involved in postanal wing determination of aphids. However, reducing amino acid content in the diet or inhibiting TOR with rapamycin resulted in a decrease of the winged morph, suggesting that the lower amino acid levels or TOR activity was not responsible for the higher proportion of winged morph on the artificial diet. These results suggest that nutritional quality, particularly sugars like sucrose and glucose, may regulate the postnatal wing morph of the pea aphid, likely via the insulin signaling pathway.

High-temperature responses of Myzus persicae and its parasitoid Aphidius gifuensis in relation to heat level, duration and developmental stage.

BACKGROUND: Understanding how parasitoids respond to temperature is crucial for improving biological control strategies under the context of global warming. This study examined the suitability of Myzus persicae and its parasitoid Aphidius gifuensis to varying temperature conditions, as well as the stage-specific response of A. gifuensis to high temperatures. RESULTS: High temperatures had a significant impact on the both M. persicae and A. gifuensis. When exposed to 36°C, M. persicae developed more slowly and produced smaller adults compared to control, regardless of the duration of exposure (2, 4 or 6 h); additionally, the survival rate of M. persicae nymphs sharply decreased under these conditions. Exposure to 36°C for 4 h negatively impacted the development of A. gifuensis. Female parasitoids exposed to 32°C developed into smaller adults, whereas males exposed to all three temperature levels were smaller compared to control group. Female parasitoids exposed to high temperatures, regardless of the specific heat level and duration, exhibited reduced longevity and decreased fecundity. None of the parasitoids exposed to 36°C for 6 h daily developed into adults. Heat treated during early developmental stages (2 and 4 days old) had a greater influence on parasitoid development, whereas heat treatment at 4 and 6 days old had a more significant impact on its fecundity. CONCLUSION: High temperatures not only directly affected the performance of A. gifuensis, but also exerted indirect effects by influencing the quality of the host aphids M. persicae. The deleterious effects of high temperature on larvae can persist into the adult stage, affecting the longevity and reproduction of adults. These findings are important for the utilization of A. gifuensis in the control of M. persicae in warming environments. © 2024 Society of Chemical Industry.

Assessing the Suitability of Chinese Cabbage as an Alternative Host for Spodoptera frugiperda (Lepidoptera: Noctuidae).

When the favored host of an herbivorous insect pest is absent, the availability of alternative host plants can maintain insect pest populations. Spodoptera frugiperda (Lepidoptera: Noctuidae) is a major invasive, polyphagous insect pest in China. To investigate the suitability of Chinese cabbage as an alternative host for S. frugiperda, oviposition preferences and life history traits were determined for S. frugiperda on Chinese cabbage, corn, and winter wheat over three generations. Results showed that S. frugiperda females preferred to lay their eggs on corn compared to winter wheat and Chinese cabbage. The survival rate of S. frugiperda decreased after switching from corn to Chinese cabbage, only 6% of individuals successfully pupated in the third generation. In addition, S. frugiperda reared on Chinese cabbage had lower pupal weight and fecundity. Winter wheat was a good host for S. frugiperda; although the survival rate decreased when S. frugiperda switched from corn to winter wheat in the parental generation, the survival rate increased over the next two generations to be as high as those reared on corn. Chinese cabbage is not a good long-term host for S. frugiperda, but it could maintain the pest population for at least two generations when more suitable host plants are unavailable. These results will inform management strategies for S. frugiperda.

Avoidance of parasitized host by female wasps of Aphidius gifuensis (Hymenoptera: Braconidae): The role of natal rearing effects and host availability?

Natal rearing experience of animals may affect their behaviors, such as habitat selection and oviposition decision. As part of the overall fitness of insect parasitoids, successful host discrimination (distinguishing parasitized hosts from unparasitized hosts) is of paramount importance. In this study we examined whether and how parasitoids' natal rearing experience would affect their host discrimination ability according to host availability. We established separate colonies of Aphidius gifuensis Ashmead by continual rearing on two hosts, Sitobion avenae F. and Myzus persicae (Suzler), and quantified self superparasitism and self superparasitism versus parasitism ratio for the four combinations of parasitoid colonies and host species (S. aveane and M. persicae) at four host densities (30, 50, 100 or 150 per plant). Results showed that self superparasitism of M. persicae by A. gifuensis reared on S. avenae was significantly higher than by those reared on M. persicae, no matter whether the host densities were 30, 50, 100 or 150. Aphidius gifuensis reared on M. persicae significantly superparasitized more S. avenae than those reared on S. aveane only when host density was 30. Self superparasitism versus parasitism ratio of A. gifuensis from both colonies was always lower on natal hosts than on new hosts, and the difference was more pronounced as the host density decreased. These results suggested that natal rearing effects is important on host discrimination and oviposition decision of the parasitoid A. gifuensis. These effects promoted the parasitoid's host adaptation and made them confer greater fitness.