Diversity of Cellulolytic Microorganisms Associated with the Subterranean Termite Reticulitermes grassei.

Reticulitermes grassei is a subterranean termite species that forages on woody structures of the Iberian Peninsula, and is often a building and crops pest. A total of 23 microorganisms associated with the activity of R. grassei were isolated from colonized ecosystems in southern Spain. They were morphologically and molecularly characterized, with fungi being the most prevalent ones. The fungi showed high values of optimum growth temperature, suggesting that they could be able to survive and develop in warm regions. Their cellulolytic activity was tested in carboxymethylcellulose (CMC) agar, concluding that all fungal isolates produce cellulases, and the enzymatic index (EI) was revealed in CMC agar with Gram's iodine solution, with Penicillium citrinum showing the highest EI and Trichoderma longibrachiatum the highest mycelial growth rate on CMC. A preliminary microorganism dispersion assay was carried out with the termites, concluding that these insects may have a positive influence on fungal dispersion and the subsequent colonization of new substrates. Our study suggests that fungi associated with R. grassei may potentially be of interest in biotechnological fields such as biofuel production and the food industry.

Metagenomic 16S rRNA amplicon data of gut microbial diversity in three species of subterranean termites (Coptotermes gestroi, Globitermes sulphureus and Macrotermes gilvus).

In this paper, we present the metagenomic dataset of gut microbial DNA of the lower group of subterranean termites, i.e. Coptotermes gestroi, and the higher groups, i.e. Globitermes sulphureus and Macrotermes gilvus, in Penang, Malaysia. Two replicates of each species were sequenced using Next-Generation Sequencing (Illumina MiSeq) and analysed via QIIME2. The results returned with 210,248 sequences in C. gestroi, 224,972 in G. sulphureus, and 249,549 in M. gilvus. The sequence data were deposited in the NCBI Sequence Read Archive (SRA) under BioProject number of PRJNA896747. The community analysis showed that Bacteroidota is the most abundant phylum in C. gestroi and M. gilvus, while Spirochaetota is prevalent in G. sulphureus.

Polystyrene-Impregnated Glulam Resistance to Subterranean Termite Attacks in a Laboratory Test.

This study aimed to enhance tropical fast-growing tree species' resistance to subterranean termite (Coptotermes curvignathus) attacks through the manufacturing of polystyrene glued-laminated timber (glulam). Three young tropical wood species, namely manii (Maesopsis eminii), mangium (Acacia mangium), and rubber-wood (Hevea brasiliensis), were cut into laminae. After drying, the laminae were impregnated with styrene monomer, then polymerized using potassium peroxydisulfate as a catalyst and heat. The polystyrene-impregnated laminae were constructed using isocyanate glue and a cold press for three-layered glulam. Untreated or control glulam and solid wood specimens were also prepared. The specimens of each wood species and wood products (solid wood, control glulam, and polystyrene glulam) were exposed to the termite in a laboratory test according to Indonesian standards. The results showed that mangium wood had better resistance to the termite attack than manii and rubber-wood, with both of those woods performing the same. Among the wood products, the glulams were equal and had higher resistance to the termite attack than solid wood. To enhance the termite resistance of polystyrene glulam, we suggest that the polymer loading of polystyrene on each lamina should be increased. In our evaluation of the products' order of priority, polystyrene glulam emerged as performing best towards subterranean termites attack.

Belowground community turnover accelerates the decomposition of standing dead wood.

Standing dead trees (snags) decompose more slowly than downed dead wood and provide critical habitat for many species. The rate at which snags fall therefore influences forest carbon dynamics and biodiversity. Fall rates correlate strongly with mean annual temperature, presumably because warmer climates facilitate faster wood decomposition and hence degradation of the structural stability of standing wood. These faster decomposition rates coincide with turnover from fungal-dominated wood decomposer communities in cooler forests to codomination by fungi and termites in warmer regions. A key question for projecting forest dynamics is therefore whether temperature effects on wood decomposition arise primarily because warmer conditions facilitate faster decomposer metabolism, or are also influenced indirectly by belowground community turnover (e.g., termites exert additional influence beyond fungal-plus-bacterial mediated decomposition). To test between these possibilities, we simulate standing dead trees with untreated wooden posts and follow them in the field across 5 yr at 12 sites, before measuring buried, soil-air interface and aerial post sections to quantify wood decomposition and organism activities. High termite activities at the warmer sites are associated with rates of postfall that are three times higher than at the cooler sites. Termites primarily consume buried wood, with decomposition rates greatest where termite activities are highest. However, where higher microbial and termite activities co-occur, they appear to compensate for one another first, and then to slow decomposition rates at their highest activities, suggestive of interference competition. If the range of microbial and termite codomination of wood decomposer communities expands under climate warming, our data suggest that expansion will accelerate snag fall with consequent effects on forest carbon cycling and biodiversity in forests previously dominated by microbial decomposers.

Termite Presence and Feeding on Loblolly Pine Wood Differs Among Four Root-Infecting Bluestain (ophiostomatoid) Fungal Species.

Bark beetles and root weevils can impact forests through tree death on landscape scales. Recently, subterranean termites have been linked to these beetles via the presence of bluestain fungi (Ascomycota: Ophiostomataceae), which are vectored to trees by beetles. However, only a small subset of bluestain species have been examined. Here, we tested whether termite-bluestain association patterns in the field reflect termite feeding preference in laboratory choice trials. We documented the presence of four bluestain fungi (Leptographium procerum (W.B. Kendr.), L. terebrantis (Barras & Perry), Grosmannia huntii (Rob.-Jeffr.), and G. alacris (T.A. Duong, Z.W. de Beer & M.J. Wingf.) in the roots of 2,350 loblolly pine trees in the southeastern United States and whether termites were present or absent on these roots and paired this with laboratory choice feeding trials. Termites were found 2.5-fold on tree roots with at least one bluestain fungus present than tree roots without bluestain fungi. Although termites in this study and others were associated with L. procerum, L. terebrantis, and marginally G. huntii, termites only showed preferential feeding on wood inoculated with G. huntii in laboratory trials. This suggests that increased termite presence on wood with bluestain fungi may be driven by factors other than increased wood palatability. Termites could thus disproportionately affect wood turnover rates for specific pools (e.g., bark beetle and root weevil attacked trees) and in some cases (e.g., G. huntii) accelerate wood decomposition. This study supports the growing evidence that the association between subterranean termites and bluestain fungi is spatially and taxonomically widespread.

Evaluation of baiting fipronil-loaded silica nanocapsules against termite colonies in fields.

Various pesticide nanocarriers have been developed. However, their pest-control applications remain limited in laboratories. Herein, we developed silica nanocapsules encapsulating fipronil (SNC) and their engineered form, poly(ethyleneimine)-coated SNC (SNC-PEI), based on recombinant catalytic modular protein D4S2 and used them against termite colonies Coptotermes lacteus in fields. To achieve this, an integrated biomolecular bioprocess was developed to produce D4S2 for manufacturing SNC containing fipronil with high encapsulation efficiency of approximately 97% at benign reaction conditions and at scales sufficient for the field applications. PEI coating was achieved via electrostatic interactions to yield SNC-PEI with a slower release of fipronil than SNC without coating. As a proof-of-concept, bait toxicants containing varied fipronil concentrations were formulated and exposed to nine termite mounds, aiming to prolong fipronil release hence allowing sufficient time for termites to relocate the baits into and distribute throughout the colony, and to eliminate that colony. Some baits were relocated into the mounds, but colonies were not eliminated due to several reasons. We caution others interested in producing bait toxicants to be aware of the multilevel resistance mechanisms of the Coptotermes spp. "superorganism".

Termiticidal activity of chitosan against the subterranean termites Reticulitermes flavipes and Reticulitermes virginicus.

BACKGROUND: Chitosan is a derivative form of chitin, which is the major component of exoskeletons of arthropods and the cell walls of fungi. The antimicrobial activity of chitosan against lepidopterans, aphids, fungi and bacteria has been extensively investigated, but only one report on the termiticidal effect of chitosan on termites has been published. In this study, we examined the termiticidal activity of chitosan by exposing single colonies of Reticulitermes flavipes (Kollar) and Reticulitermes virginicus Banks to wood treated with six different concentrations of chitosan solutions. Termite mortality and percent mass loss of wood samples after exposure to termites for 4 weeks were calculated. RESULTS: High termite mortality (≥ 94%) occurred during exposure of R. flavipes termites to chitosan-treated wood with ≥38 mg g-1 treatment concentrations (≥ 2% chitosan), while <50% termite mortality was observed at lower treatment concentrations (11-15 mg g-1 ; 0.5% and 1% chitosan). For R. virginicus, 100% mortality was observed at all levels of treatment concentrations. A decrease in the percent mass loss of the wood sample was apparent in samples treated with solutions with an increasing chitosan concentration, with a significant difference (P < 0.05) between lower and higher treatment concentrations. Treatment retention in wood samples upon leaching was also determined and showed retention levels of between 0 and 30 mg g-1 chitosan retention. CONCLUSION: This study investigated the exposure of subterranean termites to chitosan as a wood preservative. The results show that chitosan treatments at sufficiently high loadings could protect wood against termites, preferably under non-leaching conditions. © 2018 Society of Chemical Industry.

Suitability of multiple Mediterranean oak species as a food resource for Reticulitermes grassei Clément (Isoptera: Rhinotermitidae).

The subterranean termite Reticulitermes grassei Clément causes lesions in the trunk of Quercus suber L. by constructing feeding galleries, but no information is available regarding other Quercus species from the Mediterranean region. This work aimed to study the suitability of the other main oak species of Mediterranean forests as a food resource for R. grassei. Two experiments, choice and non-choice feeding, were conducted lasting for 15, 30, and 45 days each. In the non-choice experiment, termites were offered one of the following food types: Quercus suber, Quercus ilex L., Quercus faginea Lam, cork or Pinus pinea L., which was considered the control. The choice feeding experiment used all the same food types listed above, supplied simultaneously in the same container. Food selection was examined by analysing the relationships over time between surviving termites and food consumption. The results indicated that R. grassei could be considered a generalist species, as it consumed the cork and wood of all oak species, as well as displaying a clear preference for soft wood (pine). Correlation analysis indicated that consumption was not dependent on wood density. Survival of R. grassei was influenced by the time of exposure to different oak species, but a high survival rate was maintained over time in the pine treatment (upper 70% in the three experiments). Given these results, it can be concluded that all the oak species are a suitable food source for R. grassei.

Virulence evaluation of entomopathogenic fungi to subterranean termites, Globitermes sulphureus (INSECTA: ISOPTERA)

Aims: Subterranean termites, Globitermes sulphureus is one of the significant pests for agricultural crops such as coconut and oil palm, and occasionally attacks building structure in Malaysia. Efforts to control subterranean termite infestations depended heavily on liquid termiticide applications. Natural pathogen of termites such as entomopathogenic fungi (EPF) is a promising alternative to chemical control. The objective of this study was to determine the most virulent EPF such as Metarhizium anisopliae, Beauveria bassiana and Paecilomyces sp. against the subterranean termites, G. sulphureus for the development of bio-insecticide for future use of termite control. Methodology and results: Subterranean termites were collected from mound-building termites found in Universiti Malaysia Terengganu (UMT). Cultivating, harvesting and counting of conidia of EPF were carried out to prepare the desired concentrations for screening test and bioassays, which were 1×103 , 1x105 , 1×107 and control. The pathogenicity testing was observed daily within 1 week under laboratory conditions. Screening showed that M. anisopliae was found to be the most virulent compared to B. bassiana and Paecilomyces sp., achieving 100% mortality within 3-4 days. M. anisopliae was then further tested on termites and it was found that concentration of 1×107 showed the lowest LT50 value, while LC50 of M. anisopliae in 1 day was 2.0151×106 . Conclusion, significance and impact of study: It could be concluded that M. anisopliae is the most virulent EPF against termites and the most effective concentration was ±107 followed by strains of B. bassiana and Paecilomyces sp. However, there is limited field evaluation of EPF against termites in Malaysia. Evaluation on the efficiency of M. anisopliae in the field should be conducted so that its efficacy could be proven and marketed.

Evaluation of growth and foraging in laboratory colonies of Coptotermes gestroi (Isoptera, Rhinotermitidae).

Coptotermes gestroi is an exotic species in Brazil that forages on several food items at the same time. Different laboratory tests were performed with 6-year-old colonies of this termite in order to follow the development and displacement of these colonies, considering which castes and instars were transferred or moved from their original chamber. Two bioassays were carried out, one with similar alternative foods (Pinus sp. sawdust), and the other with different alternative foods (large block of Pinus taeda and small block of Pinus elliottii). The colonies of C. gestroi did not show preferences in the allocation of foragers when they had alternative similar foods. However, they were found in the chamber that contained the small block of P. elliottii, when termites had the alternative of different blocks of Pinus, indicating an environment most favorable for the nucleus of the colony (royal cup and brood). Many factors may have influenced this choice as more nutritive alimentary resource for brood or the presentation of the food, which allowed better colony accommodation. C. gestroi did not have difficulties of migration from one chamber to another and this characteristic may be a risk factor in urban infestations of this severe pest.

Sustained release of fipronil insecticide in vitro and in vivo from biocompatible silica nanocapsules.

A pesticide delivery system made of biocompatible components and having sustained release properties is highly desirable for agricultural applications. In this study, we report a new biocompatible oil-core silica-shell nanocapsule for sustained release of fipronil insecticide. Silica nanocapsules were prepared by a recently reported emulsion and biomimetic dual-templating approach under benign conditions and without using any toxic chemicals. The loading of fipronil was achieved by direct dissolution in the oil core prior to biomimetic growth of a layer of silica shell surrounding the core, with encapsulation efficiency as high as 73%. Sustained release of fipronil in vitro was tunable through control of the silica-shell thickness (i.e., 8-44 nm). In vivo laboratory tests showed that the insecticidal effect of the fipronil-encapsulated silica nanocapsules against economically important subterranean termites could be controlled by tuning the shell thickness. These studies demonstrated the effectiveness and tunability of an environmentally friendly sustained release system for insecticide, which has great potential for broader agricultural applications with minimal environmental risks.

Localized treatments using commercial dust and liquid formulations of fipronil against Coptotermes formosanus (Isoptera: Rhinotermitidae) in the laboratory.

Use of proper application methods and formulations of termiticides are important to reduce their negative impact to the environment. In this study, we conducted laboratory experiments to determine the effect of localized treatments with commercial dust and liquid formulations of fipronil against Formosan subterranean termites, Coptotermes formosanus Shiraki. The test arena consisted of a specially designed 16-chambered structure with a center chamber connected to 5 foraging chambers that themselves were connected to 10 additional foraging chambers. One peripheral chamber received a liquid or dust treatment and termites were released in the center chamber. Results showed that >91% of the termites were dead within the 9-d test period despite the localized treatment of only 1 foraging chamber. Termites that were still alive after 9 d were transferred to an untreated dish and held for 10 more days. The majority of those termites were dead and the rest were moribund on day 19. Regardless of the specific dish treated, both formulations of fipronil were found to be highly efficacious. Termites did not exhibit repellency to either formulation. Our results suggest that localized (or spot) treatment with either commercially available dust or liquid formulations of fipronil can be a viable option for control of a termite infestation where complete soil drenching is not desirable.