Biological Control Of Insect Pests Research Articles

Impact of microbial communities on floral nectar chemistry: Potential implications for biological control of pest insects

Nectar-producing plants are increasingly used in agroecosystems to provide biological control agents (BCAs) such as predatory insects and parasitoids with necessary sugars to fulfil their nutritional requirements. However, it has recently been shown that nectar is commonly infested by microorganisms which may change the chemistry of the nectar and therefore its attractiveness and nutritional suitability for insects. The aim of this study was to investigate the impact of nectar-inhabiting microorganisms on nectar chemistry of three co-flowering plant species that are commonly used to provide BCAs with sugar resources (Borago officinalis L., Centaurea cyanus L. and Symphytum officinale L.). First, we assessed the abundance and visitation rate of flower-visiting insects on these plant species. Further, we identified the culturable microbes inhabiting the floral nectar and assessed changes in pH, total sugar concentration, main nectar sugars and amino acids. Flowers of all three plant species were found to be visited by a wide range of insects, with B. officinalis being the most attractive plant species for BCAs. Nectar microbial community structure differed significantly between plant species, irrespective of experimental field site. Microbial contamination affected both sugar and amino acid concentration and composition. Especially, sucrose and the fructan sugars 1-kestose and neokestose were found at significantly lower concentrations in contaminated nectar. Further, microbial contamination resulted in a significant increase of alanine and glycine, and a decrease in threonine and valine. Further research is needed to investigate the precise impact of these changes on the efficacy of biological control agents to control pest insects.

Diversidad de Ichneumonidae (Hymenoptera) en un bosque de Pinus spp. y Juniperus flaccida en Jaumave, Tamaulipas, México

Ichneumonids are parasitoid wasps with importance in the biological control of insect pests and constitute one of the most diverse families of Hymenoptera. The objective of this research was to know the diversity of Ichneumonidae and its relationship with temperature and rainfall in one locality of Jaumave, Tamaulipas, Mexico, during one year. One Malaise tramp was operated at 1,450m in a dry forest with Pinus nelsonii, P.cembroides and Juniperus flaccida, with a small source of water near it. The number of ichneumonids collected was 1,115. Cryptinae was the subfamily best represented in number of genera and species, Pimpla the genus more abundant and Pachysomoides stupidus the species with more individuals. High diversity of this family was found in the studied locality. High correlation was found between Ichneumonidae and temperature, and a moderate correlation with rainfall. Three species are new records for Mexico and 5 for Tamaulipas, therefore 1,298 species are known in the country. This research contributes to the knowledge of Ichneumonidae in dry areas from Mexico.

Eicosanoids mediate Galleria mellonella immune response to hemocoel injection of entomopathogenic nematode cuticles.

Entomopathogenic nematodes are symbiotically associated with bacteria and widely used in biological control of insect pests. The interference of symbiotic bacteria with insect host immune responses is fairly well documented. However, knowledge of mechanisms regulating parasite–host interactions still remains fragmentary. In this study, we used nematode (Steinernema carpocapsae and Heterorhabditis bacteriophora) cuticles and Galleria mellonella larvae as parasite–host model, focused on the changes of innate immune parameters of the host in the early phase of nematode cuticle infection and investigated the role of eicosanoid biosynthesis pathway in the process. The results showed that injection of either S. carpocapsae or H. bacteriophora cuticles into the larval hemocoel both resulted in significant decreases in the key innate immune parameters (e.g., hemocyte density, microaggregation, phagocytosis and encapsulation abilities of hemocyte, and phenoloxidase and antibacterial activities of the cell-free hemolymph). Our study indicated that the parasite cuticles could actively suppress the innate immune response of the G. mellonella host. We also found that treating G. mellonella larvae with dexamethasone and indomethacin induced similar depression in the key innate immune parameters to the nematode cuticles. However, these effects were reversed when dexamethasone, indomethacin, or nematode cuticles were injected together with arachidonic acid. Additionally, we found that palmitic acid did not reverse the influence of the dexamethasone, indomethacin, or nematode cuticles on the innate immune responses. Therefore, we inferred from our results that both S. carpocapsae and H. bacteriophora cuticles inhibited eicosanoid biosynthesis to induce host immunodepression.

Bioefficacy of wild plant extract for biological control of insect pests of Bt cotton

Wild plant fruit extract such as hinganbet, Balanites roxburghii , ritthaa/soap nut, Sapindus trifoliatus , shikekaaee, Acacia concinna , Neem, Azadirachta indica , Karanj, Pongamia pinnata and vekhand, Acorus calamus L. were evaluated to screen their efficiency for the control of sucking pests of Bt cotton during Kharif 2009 to 2012 at Cotton Improvement Project, Mahatma Phule Krishi Vidyapeeth, Rahuri. All the organic pesticide treatments were superior over untreated control. Among the evaluated organic pesticides the treatment with 5 per cent hingan bet extract @ 2 litre per hectare was observed to be effective in reducing pest population in which aphids, jassids, thrips and whiteflies of 22.68, 8.16, 14.53 and 10.97 per three leaves, respectively, were recorded with the seed cotton yield of 20.77 quintal per hectare. However, this treatment was statistically at par with 5 per cent ritthaa extract @ 2 litre per hectare. The treatment with 5 per cent ritthaa extract recorded aphids, jassids, thrips and whiteflies of 23.16, 9.87, 15.34 and 12.65 per three leaves, respectively, with the seed cotton yield of 20.09 quintal per hectare. The treatment with 5 per cent NSE @ 2 litre per hectare recorded 28.96, 12.61, 17.71 and 15.18 aphids, jassids, thrips and whiteflies per three leaves, respectively, with the seed cotton yield of 12.31 quintal per hectare. The phytotoxicity studies on leaf injury on tips and leaf surface, wilting, vein necrosis, epinasty and hyponasty showed that there was no phytotoxic effect of the evaluated pesticides on cotton crop at the evaluated doses. The counts on natural enemies in the treatments with hinganbet and ritthaa extract were more or less similar to those recorded in untreated control. This clearly indicated that there was no adverse effects on natural enemies due to spraying of hinganbet and ritthhaa extract at evaluated doses.

English

Biological control of pest insects in agriculture is the focus of many studies, because of the risks in the continuous use of synthetic insecticides, which can cause resistant pests or the occurrence of secondary pests. The use of microorganisms like endophytic bacteria has been performed separately or combined with other forms of control in the Integrated Pest Management. Endophytic bacteria live inside host plants, without causing any apparent damage or pathogenicity symptom. Besides performing many functions important to the host, these microorganisms are potentially useful in agriculture, since they are capable of substituting chemical products. By performing biocontrol actions and/or promoting plant growth, these microorganisms are favoring environmental preservation and are thus identified as a viable alternative for ecologically and economically sustainable agricultural production systems. Given the above, this review aimed to present a panorama of the potential application of plant growth-promoting bacteria in the control of pest insects in agriculture, in view of the great biotechnological advances.   Key words: Endophytic bacteria, plant growth promotion, biological control.

Nonparametric Estimation of Interspecific Spatio-Temporal Niche Separation Between Two Lady Beetles (Coleoptera: Coccinellidae) inBtCotton Fields

Predaceous lady beetles are important natural enemies of many insect pests in agro-ecosystem. The altered agricultural practices associated with widespread adoption of Bt cotton may have potential effects on the spatio-temporal patterns of predaceous lady beetles, as the composition and abundance of nontarget sucking pests have been changed in Bt cotton fields. In the current study, the spatio-temporal patterns of two important lady beetles, Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) and Propylea japonica (Thunberg) (Coleoptera: Coccinellidae), were surveyed in Bt cotton fields. A nonparametric method associated with Monte Carlo tests was used to address and test whether niche segregation occurred between H. axyridis and P. japonica. The results showed that the dominant region occupied by P. japonica was toward northeast across the season, whereas H. axyridis had higher presence to the southwest. The temporal patterns of H. axyridis and P. japonica also differed significantly, and the highest levels of each species occurred in different locations from each other on each sampling date in the same Bt cotton fields. In total, there were strong spatio-temporal separation patterns between these two species in Bt cotton fields. These spatio-temporal patterns may produce complementary impacts on prey, and this in turn could be used to strengthen the biological control of insect pests by these two lady beetles.

Field Trials of a Mechanical Prototype Designed to Release Insect Predators to Control the Colorado Potato Beetle, Leptinotarsa decemlineata (Say)

The Colorado potato beetle (CPB) is a major insect pest of potato crops in many countries around the world. Chemical insecticides constitute the most widely used control method for this insect pest. To date, no registered chemical pest control product has proven effective at managing CPB on a long-term basis. Although biological control through manual release of natural enemies of CPB has been successful on a small scale, large-scale manual release of these predators is not realistic. The objective of this study was to assess the effectiveness of mechanical release of predator insects as a control method for CPB under real conditions in a potato field. The results show that the use of Podisus maculiventris second and third instar nymphs provided effective control of CPB populations throughout the growing season in Quebec, Canada. Moreover, mechanical release of these predator insects proved as efficient as manual release on potato plants. This points to the potential for using mechanical release of predator insects for biological control on a commercial scale. The tested approach based on mechanical release of beneficial insects holds promise for biological control of insect pests in many other row crops, such as eggplant, crucifers, cucurbits, onions, sweet corn, tomatoes, and strawberries.

A novel Wolbachia strain from the rice moth Corcyra cephalonica induces reproductive incompatibility in the whitefly Bemisia tabaci: sequence typing combined with phenotypic evidence.

Wolbachia are a group of maternally inherited bacteria frequently found in arthropods and filarial nematodes. They have recently attracted attention for their ecological roles in manipulating host reproduction, their potential use in biological control of pest insects and medical significance. Classification of Wolbachia strains is currently solely based on molecular methods. However, the strains even with identical sequence types may induce different host phenotypes. Here we isolated a Wolbachia strain from the rice moth Corcyra cephalonica (designated as wCcep_B_BJ), which was shown to share multilocus sequence typing and Wolbachia surface protein hypervariable region profiles with a cytoplasmic incompatibility (CI)-inducing strain in supergroup B, but the phenotype wCcep_B_BJ may induce needs to be determined. We thus transinfected it into the whitefly Bemisia tabaci harbouring an A-Wolbachia through nymphal microinjection. Fluorescent in situ hybridization demonstrated that wCcep_B_BJ was successfully transinfected into B. tabaci and transmitted to offspring through host eggs. Reciprocal cross showed that wCcep_B_BJ induced a strong bidirectional CI in the transinfected host without imposing a significant cost on female fecundity. Our results suggest that wCcep_B_BJ may be a promising strain for biocontrol of B. tabaci, an important agricultural pest insect.

Modifying soil to enhance biological control of belowground dwelling insects in citrus groves under organic agriculture in Florida

An emerging organic citrus industry in Florida could benefit greatly from effective, non-conventional methods to mitigate losses from pests and diseases. We studied part of a soil food web in an organic orchard to learn ways to conserve and enhance biological control of insect pests by native entomopathogenic nematodes (EPNs). We evaluated two OMRI (Organic Materials Review Institute) approved cultural practices: (i) a mulch of commercially pelleted chicken manure, (ii) a commercial formulation of Purpureocillium lilacinus, and (iii) an un-amended control. Several soil nutrients (i.e. nitrogen, phosphate, and potassium) were affected by the amendments, but initial equilibrium values (T0) were restored by the last sampling time (T12). The plant parasitic nematode Tylenchulus semipenetrans increased in both treatments compared to the untreated control at T3 (P<0.05). The oomycete Phytophthora nicotianae increased in the P. lilacinus plots at T1, marginally at T12, but decreased at T6 and T9. Steinernema diaprepesi, Heterorhabditis indica and Heterorhabditis zealandica were the only EPNs regularly detected in the orchard. Mulch increased numbers of H. zealandica at T6 and T9 (P<0.05) and free living nematodes at T12 (P<0.01). The nematophagous fungus (NF) P. lilacinus persisted in plots where it was augmented (P<0.05), reaching a maximum level at T3 that was 17.5-fold greater than that in controls. Numbers of Paenibacillus sp. were directly related to both those of S. diaprepesi and Acrobeloides-group nematodes (P<0.01), but inversely to the FLN counts (P<0.05). The application of these two amendments did not produce strong changes in the EPN community but decreased the emergence from soil of adult Diaprepes abbreviatus, a root weevil pest. Thus, both amendments might contribute to citrus pest management under organic production.

Thuringiensin: a toxin from Bacillus thuringiensis

Bacillus thuringiensis ( Bt ) is an entomopathogenic bacteria widely used in practice for biological control of insect pests, nematodes and disease vectors. Your toxicity is related to the ability to produce many virulence factors, including thuringiensins (β-exotoxins). Most toxins produce by this microorganism are highly specific, therefore the use of it in biological control is considered environmentally safe and so this bacteria is extensively used in the production of biological insecticides and genetically modified plants. However, the thuringiensin is considered toxic to almost all life forms, including humans, due to its ability to inhibit the biosynthesis of RNA polymerase, an enzyme essential to the transfer of genetic information in almost all organisms. This way, the release of new strains of Bt with insecticidal properties for the biological control of pests must pass by verification of the absence of production of exotoxin, so that non-target organisms are not affected and the use of Bt in this field remains safe. Thus, this revision will discussed the knowledge about features, structure, genetic determinants, biosynthesis, mechanism of action, insecticide spectrum, security assessment and procedures for identification of thuringiensin in Bt strains.

EFFECT OF SOME BIOINSECTICIDES ON THE PREDATOR Chrysoperla carnea (STEPHENS).

Chrysoperla carnea (Stephens), (aphid lion, green lacewing) larvae active predators and feed on aphids and other small insects. It has been used in the biological control of insect pests on crops. While The adults feed on nectar, pollen and aphid honeydew and are not predatory Tracer (Spinosad) is primarily a stomach poison with some contact activity and is particularly active against Lepidoptera and Diptera. In this study, tested the effect of bio-pesticide Tracer on percentage of mortality on different larval instars of aphid lion, The results showed 63% mortality of first instar larvae after 72 h of exposure in high concentration when recorded 52% and 30% mortality of second and third instars larvae after the same time The study has proved that, the mortality percentages for the first instar larvae were high, But they modularity in second instar and no significant in third instar.

A virulence factor encoded by a polydnavirus confers tolerance to transgenic tobacco plants against lepidopteran larvae, by impairing nutrient absorption.

The biological control of insect pests is based on the use of natural enemies. However, the growing information on the molecular mechanisms underpinning the interactions between insects and their natural antagonists can be exploited to develop “bio-inspired” pest control strategies, mimicking suppression mechanisms shaped by long co-evolutionary processes. Here we focus on a virulence factor encoded by the polydnavirus associated with the braconid wasp Toxoneuron nigriceps (TnBV), an endophagous parasitoid of noctuid moth larvae. This virulence factor (TnBVANK1) is a member of the viral ankyrin (ANK) protein family, and appears to be involved both in immunosuppression and endocrine alterations of the host. Transgenic tobacco plants expressing TnBVANK1 showed insecticide activity and caused developmental delay in Spodoptera littoralis larvae feeding on them. This effect was more evident in a transgenic line showing a higher number of transcripts of the viral gene. However, this effect was not associated with evidence of translocation into the haemocoel of the entire protein, where the receptors of TnBVANK1 are putatively located. Indeed, immunolocalization experiments evidenced the accumulation of this viral protein in the midgut, where it formed a thick layer coating the brush border of epithelial cells. In vitro transport experiments demonstrated that the presence of recombinant TnBVANK1 exerted a dose-dependent negative impact on amino acid transport. These results open new perspectives for insect control and stimulate additional research efforts to pursue the development of novel bioinsecticides, encoded by parasitoid-derived genes. However, future work will have to carefully evaluate any effect that these molecules may have on beneficial insects and on non-target organisms.

The impact of prairie strips on aphidophagous predator abundance and soybean aphid predation in agricultural catchments.

Reconstructing prairie vegetation in row crop-dominated agricultural landscapes may contribute to several ecosystem services, including the biological control of insect pests, such as the soybean aphid Aphis glycines Matsumura. The influence of the amount and configuration of reconstructed prairie vegetation on the delivery of ecosystem services was investigated in several small catchments at Neal Smith National Wildlife Refuge in Iowa. Treatments include catchments entirely in row crops under a no-till, corn-soybean (Zea mays L.-Glycine max [L.] Merrill) rotation, catchments with 10% of the land in prairie located at the base, and catchments with 10 or 20% of the land in multiple contour strips of prairie. During 2009 and 2011 growing seasons, we measured abundance and diversity of aphidophagous insect predators in response to treatment and habitat type (i.e., soybean, prairie). In 2011, we further studied the biological control of soybean aphids by artificially infesting uncaged and caged plants to prevent exposure from predators. While aphidophagous predators were more abundant in prairie, populations of key aphid predators did not significantly differ among treatments. Biological control of the soybean aphid did not differ among treatments or with distance from prairie. Our results suggest that prairie strips, in addition to providing soil and water quality benefits, may increase the populations of beneficial insects, but may not directly impact biocontrol. We propose several hypotheses to explain why we did not observe more soybean aphid predation with the increased abundance of aphidophagous predators in catchments containing prairie.

Complete genome sequence of the first non-Asian isolate of Bombyx mori nucleopolyhedrovirus.

Brazil is one of the largest silk producers in the world. The domesticated silkworm (Bombyx mori) was formally introduced into the country in the twentieth century, and the state of Paraná is the main national producer. During larval stages, B. mori can be afflicted by many different infectious diseases, which lead to substantial losses in silk production. In this work, we describe the structure and complete genome sequence of the first non-Asian isolate of Bombyx mori nucleopolyhedrovirus (BmNPV), the most important silkworm pathogen. The BmNPV-Brazilian isolate is a nucleopolyhedrovirus with singly enveloped nucleocapsids within polyhedral occlusion bodies. Its genome has 126,861 bp with a G + C content of 40.4 %. Phylogenetic analysis clustered the virus with the Japanese strain (BmNPV-T3). As expected, we have detected intra-population variability in the virus sample. Variation along homologous regions (HRs) and bro genes was observed; there were seven HRs, deletion of bro-e, and division of bro-a into two ORFs. The study of baculoviruses allows for a better understanding of virus evolution providing insight for biological control of insect pests or protection against the pernicious disease caused by these viruses.

Tres especies nuevas de Encarsia (Hymenoptera: Chalcidoidea: Aphelinidae) de México

La familia Aphelinidae es una de las más importantes en el control biológico de insectos plaga a nivel mundial, incluye 34 géneros y aproximadamente 1,300 especies, con 12 géneros y 184 especies en México. El género Encarsia es el más diverso con 409 especies y 94 en México. En el presente trabajo se describen e ilustran tres especies nuevas: Encarsia antennata sp. n. de Baja California Sur, E. caudata sp. n. de Nuevo León y E. oaxaca sp. n. de Oaxaca y Tamaulipas.

Identification of distinct Bacillus thuringiensis 4A4 nematicidal factors using the model nematodes Pristionchus pacificus and Caenorhabditis elegans.

Bacillus thuringiensis has been extensively used for the biological control of insect pests. Nematicidal B. thuringiensis strains have also been identified; however, virulence factors of such strains are poorly investigated. Here, we describe virulence factors of the nematicidal B. thuringiensis 4A4 strain, using the model nematodes Pristionchus pacificus and Caenorhabditis elegans. We show that B. thuringiensis 4A4 kills both nematodes via intestinal damage. Whole genome sequencing of B. thuringiensis 4A4 identified Cry21Ha, Cry1Ba, Vip1/Vip2 and β-exotoxin as potential nematicidal factors. Only Cry21Ha showed toxicity to C. elegans, while neither Cry nor Vip toxins were active against P. pacificus, when expressed in E. coli. Purified crystals also failed to intoxicate P. pacificus, while autoclaved spore-crystal mixture of B. thuringiensis 4A4 retained toxicity, suggesting that primary β-exotoxin is responsible for P. pacificus killing. In support of this, we found that a β-exotoxin-deficient variant of B. thuringiensis 4A4, generated by plasmid curing lost virulence to the nematodes. Thus, using two model nematodes we revealed virulence factors of the nematicidal strain B. thuringiensis 4A4 and showed the multifactorial nature of its virulence.

The effect of semi-natural habitats on aphids and their natural enemies across spatial and temporal scales

Semi-natural habitats in agricultural landscapes are generally assumed to enhance the biological control of insect pests based on native beneficial insects, by providing alternative prey and hosts, resources and refuges for overwintering. We hypothesized that natural enemies of winter wheat aphids should arrive sooner in fields near semi-natural habitats. We compared aphid, hoverfly (larvae and eggs) and parasitized aphid (mummies) abundances in 54 winter wheat fields located in southern France from 2003 to 2007. Six surveys were recorded each spring and were split into the early period (defined as the period before the peak of aphid growth) and the late period (after the peak). The wheat fields differed by their surrounding landscape composition measured as the proportion of semi-natural habitats (woods, hedges and grasslands), at three different spatial scales: 200m, 500m, and 1200m. Despite great variability in abundance data between years, the abundance of hoverflies appeared more sensitive to landscape composition than aphid abundance was. Early abundance for both aphids and hoverflies was positively related to wood cover, but not late abundance in spring. The abundance of hoverflies was positively related to hedge and grassland cover at all spatial scales and both periods considered. Aphid parasitism was higher near hedges at the small spatial scale late in the spring. Our results confirmed that higher proportions of semi-natural habitats in agricultural landscapes enhance the biological control of pests, but this effect depends on the spatial scale, the time period in the spring and the natural enemies considered.

Ion-beam and gamma-ray irradiations induce thermotolerant mutants in the entomopathogenic fungus Metarhizium anisopliae s.l.

Entomopathogenic fungi, such as Metarhizium anisopliae (Metch.) Sorokin, are important agents for the biological control of insect pests. However, these fungi are not compatible with high temperatures. In this study, mutagenesis using ion beams or gamma rays was used to generate five potentially thermotolerant mutants from two wild-type isolates of M. anisopliae (two using ion beams and three using gamma rays). The mutant isolates had a higher upper thermal limit for vegetative growth compared to the wild types (by 2–3°C) and enhanced tolerance to wet–heat stress of 45°C for conidial germination. At 25°C and 30°C, most mutants were as virulent to maize weevil adults as the wild type, however, one mutant produced using ion beams almost lost virulence entirely. These results indicate that ion beams and gamma rays are useful tools for improving biological characteristics, such as thermotolerance, in entomopathogenic fungi, but that mutants must be carefully evaluated for unpredictable negative side effects.

Management of Insect Pests by Microorganisms

Insects, like other organisms, are susceptible to a variety of diseases caused by bacteria, viruses, fungi and protozoans, and these pathogens are exploited for biological control of insect pests through introductory or inundative applications. Microbial pathogens of insects are intensively investigated to develop environmental friendly pest management strategies in agriculture and forestry. In this paper, the scope for utilization of insect pathogens in pest management in the world and India is reviewed. The most successfully utilized insect pathogen is the bacterium, Bacillus thuringiensis (Bt) which is used extensively for management of certain lepidopteran pests. In India, mostly imported products of Bt kurstaki have been used, which are expensive and there is an urgent need to develop aggressive indigenous Bt strains against various pests. Baculoviruses comprising nuclear polyhedrosis virus (NPV) and granulosis virus (GV) have been successfully used as insect pathogens because of their high virulence and specificity. NPV and GV formulations are used for lepidopteran pests like Helicoverpa armigera (HaNPV) and Spodoptera litura (SlNPV) in India, besides Anticarsia gemmatalis NPV in Brazil, Lymanttria disper NPV, Orgyia pseudotsugata NPV in USA and GV of Pieris rapae in China. Lack of easy mass multiplication methods for the commercial production of baculoviruses calls for R&D to develop production in insect tissue cultures. Entomopathogenic fungi like Beauveria bassiana, B. brongniartii, Metarhizium anisopliae, M. anisopliae var. acridium, Lecanicillium spp., Hirsutella thompsonii, Nomuraea rileyi and Isaria fumosorosea are gaining importance in the crop pest control in recent years due to the simpler, easier and cheaper mass production techniques. Environmental humidity and temperature play an important role in the infection and sporulation of these fungi and as such they are highly suitable during cool and humid cropping seasons. Successful uses include M. anisopliae var. acridium for locust control in Africa, Australia and China, M. anisopliae in sugarcane spittle bug management in Brazil and pine moth (Dendrolimus spp.) control in China using B. bassiana. Since talc based formulations of these fungi have limited shelf life of 3-4 months, alternative formulations with longer shelf life (12-18 months) have to be developed besides suitable oil based formulations for dry land agriculture. There is a scope to utilize the biodiversity of Entomophthorale group of fungi like Entomophthora, Zoophthora, Neozygites etc., which have potential for management of aphids, thrips and lepidopteran pests.

The gut microbiota of larvae of Rhynchophorus ferrugineus Oliver (Coleoptera: Curculionidae).

BackgroundThe red palm weevil (RPW) Rhynchophorus ferrugineus Olivier (Coleoptera: Curculionidae) is one of the major pests of palms. The larvae bore into the palm trunk and feed on the palm tender tissues and sap, leading the host tree to death. The gut microbiota of insects plays a remarkable role in the host life and understanding the relationship dynamics between insects and their microbiota may improve the biological control of insect pests. The purpose of this study was to analyse the diversity of the gut microbiota of field-caught RPW larvae sampled in Sicily (Italy).ResultsThe 16S rRNA gene-based Temporal Thermal Gradient Gel Electrophoresis (TTGE) of the gut microbiota of RPW field-trapped larvae revealed low bacterial diversity and stability of the community over seasons and among pools of larvae from different host trees. Pyrosequencing of the 16S rRNA gene V3 region confirmed low complexity and assigned 98% of the 75,564 reads to only three phyla: Proteobacteria (64.7%) Bacteroidetes (23.6%) and Firmicutes (9.6%) and three main families [Enterobacteriaceae (61.5%), Porphyromonadaceae (22.1%) and Streptococcaceae (8.9%)]. More than half of the reads could be classified at the genus level and eight bacterial genera were detected in the larval RPW gut at an abundance ≥1%: Dysgonomonas (21.8%), Lactococcus (8.9%), Salmonella (6.8%), Enterobacter (3.8%), Budvicia (2.8%), Entomoplasma (1.4%), Bacteroides (1.3%) and Comamonas (1%). High abundance of Enterobacteriaceae was also detected by culturing under aerobic conditions. Unexpectedly, acetic acid bacteria (AAB), that are known to establish symbiotic associations with insects relying on sugar-based diets, were not detected.ConclusionsThe RPW gut microbiota is composed mainly of facultative and obligate anaerobic bacteria with a fermentative metabolism. These bacteria are supposedly responsible for palm tissue fermentation in the tunnels where RPW larvae thrive and might have a key role in the insect nutrition, and other functions that need to be investigated.