Demographic comparison and population projection of Rhynchophorus ferrugineus (Coleoptera: Curculionidae) reared on sugarcane at different temperatures

Demographic responses of Tribolium castaneum (Coleoptera: Tenebrionidae) to different temperatures in soft wheat flour

The red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) is one of the most dangerous insects of a wide spectrum of stored products around the globe. The population growth of this species is affected by temperature. However, there are no data on comparative demographic parameters (i.e., net reproductive rate, intrinsic rate of increase, finite rate of increase, mean generation time and doubling time) in different temperatures, parameters that allow the in-depth exploration of its survival, mortality and reproduction patterns. This study evaluated egg-to-adult development, adult mortality and female fecundity on white soft wheat flour at 20, 25, 30 and 32.5 °C. The net reproductive rate increased from 0.08 females/female at 20 °C to 11.77 females/female at 25 °C and 102.07 females/female at 30 °C, followed by a decrease to 10.73 females/female at 32.5 °C. The lowest values of the intrinsic rate of increase and the finite rate of increase were observed at 20 °C (- 0.0105 females/female/day and 0.9895, respectively) and the highest at 30 °C (0.0348 females/female/day and 1.0354, respectively). While the mean generation time did not differ significantly between 20 and 25 °C (249.9 and 225.5 days, respectively), this decreased to 132.8 and 115.1 days at 30 and 32.5 °C, respectively. The value of the doubling time was negative at 20 °C (- 67.5 days), increased to 19.9, 34.0 and 63.9 days at 30, 32.5 and 25 °C, respectively. Using the non-linear Briere model, the lower threshold for T. castaneum population increase was estimated to be 22.2 °C, the upper threshold at 33.2 °C, and the temperature for maximum growth rate was 30.1 °C. Survival analysis indicated that temperature also affected the mortality risk of T. castaneum. The mean survival time increased from 112.1 days at 20 °C to 462.4 days at 25 °C, followed by a decrease to 206.5 and 64.5 days at 30 and 32.5 °C, respectively. We expect these results to be useful for the prediction of the population growth, the potential expansion and consequently management of T. castaneum.

Neuropeptides and G-Protein Coupled Receptors (GPCRs) in the Red Palm Weevil Rhynchophorus ferrugineus Olivier (Coleoptera: Dryophthoridae)

The red palm weevil Rhynchophorus ferrugineus is a devastating, invasive pest that causes serious damages to palm trees, and its invasiveness depends on its strong ability of physiological and behavioral adaptability. Neuropeptides and their receptors regulate physiology and behavior of insects, but these protein partners have not been identified from many insects. Here, we systematically identified neuropeptide precursors and the corresponding receptors in the red palm weevil, and analyzed their tissue expression patterns under control conditions and after pathogen infection. A total of 43 putative neuropeptide precursors were identified, including an extra myosuppressin peptide was identified with amino acid substitutions at two conserved sites. Forty-four putative neuropeptide receptors belonging to three classes were also identified, in which neuropeptide F receptors and insulin receptors were expanded compared to those in other insects. Based on qRT-PCR analyses, genes coding for several neuropeptide precursors and receptors were highly expressed in tissues other than the nervous system, suggesting that these neuropeptides and receptors play other roles in addition to neuro-reception. Some of the neuropeptides and receptors, like the tachykinin-related peptide and receptor, were significantly induced by pathogen infection, especially sensitive to Bacillus thuringiensis and Metarhizium anisopliae. Systemic identification and initial characterization of neuropeptides and their receptors in the red palm weevil provide a framework for further studies to reveal the functions of these ligand- and receptor-couples in regulating physiology, behavior, and immunity in this important insect pest species.

Preparation of Red Palm Weevil Rhynchophorus Ferrugineus (Olivier) (Coleoptera: Dryophthoridae) Germ-free Larvae for Host-gut Microbes Interaction Studies

Red palm weevil (RPW), Rhynchophorus ferrugineus Olivier, is a devastating pest of palm trees worldwide. RPW gut is colonized by diverse bacterial species which profoundly influence host development and nutritional metabolism. However, the molecular mechanisms behind the interactions between RPW and its gut microbiota remain mostly unknown. Antibiotics are usually employed to remove gut bacteria to investigate the impact of gut bacteria on insect fitness. However, administration of antibiotics cannot thoroughly remove gut bacteria for most insect species. Therefore, establishing germfree (GF) organisms is a powerful way to reveal the mutual interactions between gut bacteria and their insect hosts. Here, we describe a protocol to generate and maintain RPW GF larvae, being completely devoid of gut bacteria in laboratory. RPW GF larvae were established from the dechorionated fresh eggs which were reared on the sterilized artificial food under axenic conditions. The establishment of GF larvae set a solid foundation to deeply elucidate the molecular mechanisms behind the interactions between RPW and its gut microbiota.

An IMD-like pathway mediates the intestinal immunity to modulate the homeostasis of gut microbiota in Rhynchophorus ferrugineus Olivier (Coleoptera: Dryophthoridae)

Most animals have established the mutualistic interactions with their intestinal microbes which provide multiple benefits to their host physiology. However, the mechanisms behind hosts determine the load and composition of gut microbiota are still poorly understood outside dipteran insects. Here, the gene, encoding the NF-κB-like transcription factor Relish, being designated as RfRelish, was identified and analyzed in red palm weevil (RPW), Rhynchophorus ferrugineus Olivier. We revealed that the abundance of RfRelish transcripts in the fat body, hemolymph and gut are significantly higher than that in non-immunity-related tissues, and its expression level can be markedly induced by bacterial challenges. When RfRelish was silenced, the ability of individuals to clear the pathogenic bacteria in body cavity and gut was significantly compromised, suggesting that both the systemic and gut local immunity were impaired dramatically by RfRelish knockdown. Additionally, the silenced insects exhibited increased gut bacterial load, and the relative abundance of some gut bacteria was changed as compared to controls. Collectively, our findings demonstrate that the IMD-like pathway restricts the proliferation of gut bacteria and shapes the commensal community structure in the intestine of R. ferrugineus by mediating the secretion of antimicrobial peptides. We provide a striking example on how an insect pest maintains the homeostasis of gut microbiota via a conserved immune pathway without compromising the advantages of the mutualistic relationships.

The Gut Entomotype of Red Palm Weevil Rhynchophorus ferrugineus Olivier (Coleoptera: Dryophthoridae) and Their Effect on Host Nutrition Metabolism

For invasive insects, the potential roles of gut microbiota in exploiting new food resources and spreading remain elusive. Red palm weevil (RPW), Rhynchophorus ferrugineus Olivier, is an invasive destructive pest which feeds on nutrient-poor tender tissues and has caused extensive mortality of palm trees. The microbes associated with insects can improve their nutrition assimilation. However, experimental evidence on the interactions between RPW and its gut microbiota is still absent. The aim of this study is to determine the dynamics changes and the bacterial entomotype in the RPW gut and its potential physiological roles. Here, we confirmed RPW harbors a complex gut microbiota mainly constituted by bacteria in the families Enterobacteriaceae, Lactobacillaceae, Entomoplasmataceae, and Streptococcaceae. RPW gut microbiota exhibited a highly stable microbial community with low variance in abundance across different life stages and host plants. Furthermore, the abundance of Enterobacteriaceae was markedly increased but that of Acetobacteraceae was reduced significantly after administration of antibiotics. Although no significant effects were found on the body weight gain of RPW larvae, these alterations dramatically decreased the concentration of hemolymph protein and glucose while that of hemolymph triglyceride increased. In the gut of wild-caught RPW larvae, seven bacterial species in the genera Klebsiella, Serratia, Enterobacter, and Citrobacter were shown to have an ability to degrade cellulose. Together, RPW accommodate a stable gut microbiota which can degrade plant polysaccharides and confer their host optimal adaptation to its environment by modulating its metabolism.

Experimental and numerical evaluations on palm microwave heating for Red Palm Weevil pest control

The invasive Red Palm Weevil is the major pest of palms. Several control methods have been applied, however concern is raised regarding the treatments that can cause significant environmental pollution. In this context the use of microwaves is particularly attractive. Microwave heating applications are increasingly proposed in the management of a wide range of agricultural and wood pests, exploiting the thermal death induced in the insects that have a thermal tolerance lower than that of the host matrices. This paper describes research aiming to combat the Red Palm pest using microwave heating systems. An electromagnetic-thermal model was developed to better control the temperature profile inside the palm tissues. In this process both electromagnetic and thermal parameters are involved, the latter being particularly critical depending on plant physiology. Their evaluation was carried out by fitting experimental data and the thermal model with few free parameters. The results obtained by the simplified model well match with both that of a commercial software 3D model and measurements on treated Phoenix canariensis palms with a ring microwave applicator. This work confirms that microwave heating is a promising, eco-compatible solution to fight the spread of weevil.