Hosting certain facultative symbionts modulates the phenoloxidase activity and immune response of the pea aphid Acyrthosiphon pisum

Regulation of melanization in aphids by parasitoid wasp venom proteins enhances mummification

BACKGROUND

Interactions between parasitic insects and their hosts demonstrate the complexity of evolutionary processes. Specifically, the parasitoid wasp Aphidius ervi manipulates its host, the pea aphid Acyrthosiphon pisum, through strategic venom injection to enhance mummification. This study explores how this venom affects the aphid's immune system, particularly targeting the activity of the phenoloxidase (PO) enzyme.

RESULTS

Following the injection of venom from A. ervi, significant changes were observed in the expression of immune-related genes in A. pisum, especially notable expression changes of ApPPOs and a reduction of PO activity. Multi-omics sequencing identified 74 potential venom proteins in the venom gland of A. ervi, including serine protease homolog 1 (AeSPH1) and serine protease inhibitor (AeSPN1), hypothesized to regulate PO activity. The injection of recombinant protein AeSPH1 and AeSPN1 into the A. pisum hemocoel selectively reduced the expression of ApPPO1, without affecting ApPPO2, and effectively suppressed melanization. Moreover, RNAi targeting AeSPH1 significantly reduced the mummification rate in A. pisum population parasitized by A. ervi.

CONCLUSION

Our findings clarify the complex biochemical mechanisms underlying host-wasp interactions and highlight potential avenues for developing targeted biological control strategies. © 2024 Society of Chemical Industry.

Heavy metal exposure reduces larval gut microbiota diversity of the rice striped stem borer, Chilo suppressalis

Cadmium (Cd), a widely distributed environmental pollutant in agroecosystems, causes negative effects on crops and herbivores through bottom-up processes. The gut microbial community of an insect can play a critical role in response to metal stress. To understand how microbiota affect the stress responses of organisms to heavy metals in agroecosystems, we initially used 16S rRNA sequencing to characterize the larval gut microbiota of Chilo suppressalis, an important agricultural pest, exposed to a diet containing Cd. The species richness, diversity, and composition of the gut microbial community was then analyzed. Results revealed that while the richness (Chao1 and ACE) of gut microbiota in larvae exposed to Cd was not significantly affected, diversity (Shannon and Simpson) was reduced due to changes in species distribution and relative abundance. Overall, the most abundant genus was Enterococcus, while the abundance of the genera Micrococcaceae and Faecalibaculum in the control significantly superior to that in Cd-exposed pests. Phylogenetic investigation of microbial communities by the reconstruction of unobserved states (PICRUSt) showed that the intestinal microorganisms appear to participate in 34 pathways, especially those used in environmental information processing and the metabolism of the organism. This study suggests that the gut microbiota of C. suppressalis are significantly impacted by Cd exposure and highlights the importance of the gut microbiome in host stress responses and negative effects of Cd pollution in agroecosystems.

The endosymbiont Serratia symbiotica improves aphid fitness by disrupting the predation strategy of ladybeetle larvae

Aphids, the important global agricultural pests, harbor abundant resources of symbionts that can improve the host adaptability to environmental conditions, also control the interactions between host aphid and natural enemy, resulting in a significant decrease in efficiency of biological control. The facultative symbiont Serratia symbiotica has a strong symbiotic association with its aphid hosts, a relationship that is known to interfere with host-parasitoid interactions. We hypothesized that Serratia may also influence other trophic interactions by interfering with the physiology and behavior of major predators to provide host aphid defense. To test this hypothesis, we investigated the effects of Serratia on the host aphid Acyrthosiphon pisum and its predator, the ladybeetle Propylaea japonica. First, the prevalence of Serratia in different A. pisum colonies was confirmed by amplicon sequencing. We then showed that harboring Serratia improved host aphid growth and fecundity but reduced longevity. Finally, our research demonstrated that Serratia defends aphids against P. japonica by impeding the predator's development and predation capacity, and modulating its foraging behavior. Our findings reveal that facultative symbiont Serratia improves aphid fitness by disrupting the predation strategy of ladybeetle larvae, offering new insight into the interactions between aphids and their predators, and providing the basis of a new biological control strategy for aphid pests involving the targeting of endosymbionts.

Endosymbionts modulate virus effects on aphid-plant interactions

Vector-borne pathogens frequently modify traits of their primary hosts and vectors in ways that influence disease transmission. Such effects can themselves be altered by the presence of other microbial symbionts, yet we currently have limited understanding of these interactions. Here we show that effects of pea enation mosaic virus (PEMV) on interactions between host plants and aphid vectors are modulated by the presence of different aphid endosymbionts. In a series of laboratory assays, we found strong interactive effects of virus infection and endosymbionts on aphid metabolomic profiles, population growth, behavior, and virus transmission during aphid feeding. Furthermore, the strongest effects-and those predicted to favor virus transmission-were most apparent in aphid lines harboring particular endosymbionts. These findings show that virus effects on host-vector interactions can be strongly influenced by other microbial symbionts and suggest a potentially important role for such interactions in disease ecology and evolution.

Triple RNA-Seq characterizes aphid gene expression in response to infection with unequally virulent strains of the endosymbiont Hamiltonella defensa

Background

Secondary endosymbionts of aphids provide benefits to their hosts, but also impose costs such as reduced lifespan and reproductive output. The aphid Aphis fabae is host to different strains of the secondary endosymbiont Hamiltonella defensa, which encode different putative toxins. These strains have very different phenotypes: They reach different densities in the host, and the costs and benefits (protection against parasitoid wasps) they confer to the host vary strongly.

Results

We used RNA-Seq to generate hypotheses on why four of these strains inflict such different costs to A. fabae. We found different H. defensa strains to cause strain-specific changes in aphid gene expression, but little effect of H. defensa on gene expression of the primary endosymbiont, Buchnera aphidicola. The highly costly and over-replicating H. defensa strain H85 was associated with strongly reduced aphid expression of hemocytin, a marker of hemocytes in Drosophila. The closely related strain H15 was associated with downregulation of ubiquitin-related modifier 1, which is related to nutrient-sensing and oxidative stress in other organisms. Strain H402 was associated with strong differential regulation of a set of hypothetical proteins, the majority of which were only differentially regulated in presence of H402.

Conclusions

Overall, our results suggest that costs of different strains of H. defensa are likely caused by different mechanisms, and that these costs are imposed by interacting with the host rather than the host’s obligatory endosymbiont B. aphidicola.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07742-8.

Sustainable laser-based technology for insect pest control

Aphids damage directly or indirectly cultures by feeding and spreading diseases, leading to huge economical losses. So far, only the use of pesticides can mitigate their impact, causing severe health and environmental issues. Hence, innovative eco-friendly and low-cost solutions must be promoted apart from chemical control. Here, we have investigated the use of laser radiation as a reliable solution. We have analyzed the lethal dose required to kill 90% of a population for two major pest aphid species (Acyrthosiphon pisum and Rhopalosiphum padi). We showed that irradiating insects at an early stage (one-day old nymph) is crucial to lower the lethal dose without affecting plant growth and health. The laser is mostly lethal, but it can also cause insect stunting and a reduction of survivors' fecundity. Nevertheless, we did not notice any significant visible effect on the offspring of the surviving irradiated generation. The estimated energy cost and the harmless effect of laser radiation on host plants show that this physics-based strategy can be a promising alternative to chemical pesticides.