Purification and characterization of trans-permethrin metabolizing microsomal esterases from workers of the eastern subterranean termite, Reticulitermes flavipes (Kollar)

Insecticide resistance in social insects: assumptions, realities, and possibilities

Insecticide resistance is an evolved ability to survive insecticide exposure. Compared with nonsocial insects, eusocial insects have lower numbers of documented cases of resistance. Eusocial insects include beneficial and pest species that can be incidentally or purposely targeted with insecticides. The central goal of this review is to explore factors that either limit resistance or the ability to detect it in eusocial insects. We surveyed the literature and found that resistance has been documented in bees, but in other pest groups such as ants and termites, the evidence is more sparse. We suggest the path forward for better understanding eusocial resistance should include more tractable experimental models, comprehensive geographic sampling, and targeted testing of the impacts of social, symbiont, genetic, and ecological factors.

Effects of caste on the expression of genes associated with septic injury and xenobiotic exposure in the Formosan subterranean termite

As social insects, termites live in densely populated colonies with specialized castes under conditions conducive to microbial growth and transmission. Furthermore, termites are exposed to xenobiotics in soil and their lignocellulose diet. Therefore, termites are valuable models for studying gene expression involved in response to septic injury, immunity and detoxification in relation to caste membership. In this study, workers and soldiers of the Formosan subterranean termite, Coptotermes formosanus, were challenged by bacterial injection or by no-choice feeding with a sublethal concentration (0.5%) of phenobarbital. Constitutive and induced expression of six putative immune response genes (two encoding for lectin-like proteins, one for a ficolin-precursor, one for the Down syndrome cell adhesion molecule, one for a chitin binding protein, and one for the gram-negative binding protein 2) and four putative detoxification genes (two encoding for cytochrome P450s, one for glutathione S-transferase, and one for the multi antimicrobial extrusion protein), were measured via quantitative real time polymerase chain reaction and compared within and among 1) colonies, 2) treatment types and 3) castes via ANOVA. Eight genes were inducible by septic injury, feeding with phenobarbital or both. Colony origin had no effect on inducibility or differential gene expression. However, treatment type showed significant effects on the expression of the eight inducible genes. Caste effects on expression levels were significant in five of the eight inducible genes with constitutive and induced expression of most target genes being higher in workers than in soldiers.

Characterization of four esterase genes and esterase activity from the gut of the termite Reticulitermes flavipes

Four esterase genes and general esterase activity were investigated in the gut of the termite Reticulitermes flavipes. Two genes (RfEst1 and RfEst2) share significant translated identity with a number of insect JH esterases. The two remaining genes (RfEst3 and RfEst4) apparently code for much shorter proteins with similarity to fungal phenolic acid esterases involved in hemicellulose solubilization. All four genes showed consistently high midgut expression. This result was further supported by colorimetric activity assays and Native polyacrylamide gel electrophoresis, which showed significant esterase activity and a number of isoforms in the midgut. The greatest esterase activity and isoform composition were detected when alpha-naphthyl propionate was used as a substrate. Moreover, esterase activity and diverse isoforms were present in gut mitochondrial, microsomal, and cytosolic sub-cellular protein fractions, as well as in the hindgut lumen. These findings reveal an agreement between gut esterase gene expression and activity distributions, and support the idea that R. flavipes gut esterase activity is host (not symbiont)-derived. In addition, these findings support the hypotheses that termite gut esterases may play important roles in lignocellulose digestion and caste differentiation. This study provides important baseline data that will assist ongoing functional-genomic efforts to identify novel genes with roles in semiochemical, hormone, and lignocellulose processing in the termite gut.

Parallel metatranscriptome analyses of host and symbiont gene expression in the gut of the termite Reticulitermes flavipes

BACKGROUND

Termite lignocellulose digestion is achieved through a collaboration of host plus prokaryotic and eukaryotic symbionts. In the present work, we took a combined host and symbiont metatranscriptomic approach for investigating the digestive contributions of host and symbiont in the lower termite Reticulitermes flavipes. Our approach consisted of parallel high-throughput sequencing from (i) a host gut cDNA library and (ii) a hindgut symbiont cDNA library. Subsequently, we undertook functional analyses of newly identified phenoloxidases with potential importance as pretreatment enzymes in industrial lignocellulose processing.

RESULTS

Over 10,000 expressed sequence tags (ESTs) were sequenced from the 2 libraries that aligned into 6,555 putative transcripts, including 171 putative lignocellulase genes. Sequence analyses provided insights in two areas. First, a non-overlapping complement of host and symbiont (prokaryotic plus protist) glycohydrolase gene families known to participate in cellulose, hemicellulose, alpha carbohydrate, and chitin degradation were identified. Of these, cellulases are contributed by host plus symbiont genomes, whereas hemicellulases are contributed exclusively by symbiont genomes. Second, a diverse complement of previously unknown genes that encode proteins with homology to lignase, antioxidant, and detoxification enzymes were identified exclusively from the host library (laccase, catalase, peroxidase, superoxide dismutase, carboxylesterase, cytochrome P450). Subsequently, functional analyses of phenoloxidase activity provided results that were strongly consistent with patterns of laccase gene expression. In particular, phenoloxidase activity and laccase gene expression are mostly restricted to symbiont-free foregut plus salivary gland tissues, and phenoloxidase activity is inducible by lignin feeding.

CONCLUSION

To our knowledge, this is the first time that a dual host-symbiont transcriptome sequencing effort has been conducted in a single termite species. This sequence database represents an important new genomic resource for use in further studies of collaborative host-symbiont termite digestion, as well as development of coevolved host and symbiont-derived biocatalysts for use in industrial biomass-to-bioethanol applications. Additionally, this study demonstrates that: (i) phenoloxidase activities are prominent in the R. flavipes gut and are not symbiont derived, (ii) expands the known number of host and symbiont glycosyl hydrolase families in Reticulitermes, and (iii) supports previous models of lignin degradation and host-symbiont collaboration in cellulose/hemicellulose digestion in the termite gut. All sequences in this paper are available publicly with the accession numbers FL634956-FL640828 (Termite Gut library) and FL641015-FL645753 (Symbiont library).

Esterase and lipase in camel tick Hyalomma dromedarii (Acari: Ixodidae) during embryogenesis

Esterase and lipase activity showed significant changes during embryogenesis of camel tick Hyalomma dromedarii. From the elution profile of chromatography on DEAE-cellulose, six forms of H. dromedarii esterase (El to EVI) can be distinguished. Esterase EIII was purified to homogeneity after chromatography on Sepharose 6B. The molecular mass of esterase EIII was 45 kDa for the native enzyme and represented a monomer of 45 kDa by SDS-PAGE. Esterase EIII had an acidic pI at 5.3. Lipase activity was detected in the same DEAE-cellulose peaks (LI to LVI) of H. dromedarii esterases. The highest lipase activity was exhibited by lipase LIII. Esterase EIII and lipase LIII were compared with respect to Michaelis constant, substrate specificity, temperature optimum, heat stability, pH optimum, effect of metal ions and inhibitors. This study suggests that H. dromedarii lipolytic enzymes may play a central role in the interconversion of lipovitellins during embryogenesis.

United States Department of Agriculture-Agriculture Research Service research on targeted management of the Formosan subterranean termite Coptotermes formosanus Shiraki (Isoptera: Rhinotermitidae)

The Formosan subterranean termite, Coptotermes formosanus Shiraki is currently one of the most destructive pests in the USA. It is estimated to cost consumers over US dollars 1 billion annually for preventative and remedial treatment and to repair damage caused by this insect. The mission of the Formosan Subterranean Termite Research Unit of the Agricultural Research Service is to demonstrate the most effective existing termite management technologies, integrate them into effective management systems, and provide fundamental problem-solving research for long-term, safe, effective and environmentally friendly new technologies. This article describes the epidemiology of the pest and highlights the research accomplished by the Agricultural Research Service on area-wide management of the termite and fundamental research on its biology that might provide the basis for future management technologies. Fundamental areas that are receiving attention are termite detection, termite colony development, nutrition and foraging, and the search for biological control agents. Other fertile areas include understanding termite symbionts that may provide an additional target for control. Area-wide management of the termite by using population suppression rather than protection of individual structures has been successful; however, much remains to be done to provide long-term sustainable population control. An educational component of the program has provided reliable information to homeowners and pest-control operators that should help slow the spread of this organism and allow rapid intervention in those areas which it infests.

Insecticide susceptibility and detoxication enzyme activities among Coptotermes formosanus Shiraki workers sampled from different locations in New Orleans

Coptotermes formosanus Shiraki worker termites were sampled from 20 locations in the City Park area of New Orleans, LA. The termites were subsequently assayed to determine their susceptibility to cypermethrin, chlordane and chlorpyrifos, and detoxication enzyme activity. Cypermethrin was most toxic against Formosan subterranean termite workers, chlorpyrifos exhibited intermediate toxicity and chlordane was least toxic. A comparison of insecticide susceptibility between the most and least tolerant colonies revealed 1.9-, 1.7- and 1.8-fold differences in susceptibility for cypermethrin, chlorpyrifos and chlordane, respectively. As with the bioassay data, although significant differences were noted, a great deal of overlap was observed among the colonies for total cytochrome P450 content (difference of 2.2-fold between high and low value) aldrin epoxidation (3.6-fold) and cytosolic esterase (3.9-fold) activity. No significant differences were observed among the colonies for methoxyresorufin O-demethylase or glutathione S-transferase activity. Conversely, microsomal esterase activity varied greatly; a 38-fold difference was observed between the most (Cf1776) and least (Cf1387) active colonies. However, no significant correlation was observed between insecticide susceptibility and microsomal esterase activity. In fact, no significant correlations were observed between any of the enzyme activities measured and insecticide susceptibility. These results are discussed in the context of insecticide selection and future control effectiveness.