Chow-Yang Lee

Background: For decades, insecticides have been central to controlling the yellow fever mosquito, Aedes aegypti (L.), but extensive use has driven resistance development. This study investigates resistance of Ae. aegypti to pyrethroids (permethrin, deltamethrin) and organophosphates (malathion, pirimiphos-methyl) and their underlying mechanisms across Malaysia, Thailand, Indonesia, and the USA. Methods: Adult female Ae. aegypti (3–5 days old, non-blood-fed) were subjected to World Health Organization (WHO) tube bioassays using 0.4% permethrin, 0.03% deltamethrin, 5% malathion, and 60 mg/m ² pirimiphos-methyl. Each assay included four replicates of 25 mosquitoes, with mortality assessed at 24 h post-exposure. Genomic DNA was extracted from 10 resistant individuals per population, and two coding regions of the voltage-gated sodium channel (VGSC) gene (domains II and III) were amplified and sequenced to detect known and novel kdr mutations. For biochemical analysis, 40 newly emerged, non-blood-fed females per strain were individually homogenized to quantify mixed-function oxidase (MFO), esterase (α- and β-EST), glutathione S-transferase (GST), and acetylcholinesterase (AChE) activity. Results: High resistance levels were recorded in Malaysian and US Ae. aegypti strains, with low mortality ranging between 9% and 22% for pyrethroids. New mutations T1520I (8–15%) and I1011M (10–15%) were identified in Malaysian populations, the first detection of T1520I in the country, while V1016I (10%) was newly detected in Indonesian strains. Malaysian mosquitoes had multiple kdr mutations (S989P, V1016G, F1534C, and T1520I) in triple- and quadruple-haplotype combinations. The US Riverside strain showed a nine- to 10-fold increase in β-EST and three- to fivefold increase in MFO and GST activity compared to the VCRU susceptible strain, indicating strong metabolic resistance. In contrast, the highly resistant Malaysian Hamna strain exhibited no significant upregulation ( P > 0.05) in detoxifying enzymes, suggesting resistance was driven primarily by kdr mutations. Thai strains lacked kdr mutations but exhibited altered AChE (20–35% remaining activity) and elevated GST (2–3 times higher than control). Conclusions: The detection of novel kdr mutations and diverse resistance mechanisms underscores the adaptability of Ae. aegypti to insecticide pressure and highlights the urgent need for continuous monitoring and integrated resistance management strategies. Graphical

In addition to serving as a telltale sign of infestation, drywood termite fecal pellets can reveal information about the colony that produced them. In this study, the bacterial communities of fresh and aged fecal pellets of Incisitermes minor (Hagen) were investigated to test the hypothesis that patterns of bacterial succession can be used to distinguish fresh from aged pellets and therefore indicate an active infestation. Fecal pellets were collected from drywood termites that fed on either the wood they were collected from or Douglas-fir (D-fir) commercial lumber. Freshly produced, 3-mo, 6-mo, and 12-mo-old pellets underwent 16S rRNA gene sequencing to identify the bacteria present in the samples. Natural-wood pellets contained on average over five times the amount of bacterial DNA compared to D-fir pellets. Up to a 190-fold decrease in estimated bacterial DNA quantity was detected between fresh to 12-mo-old pellets. Comparisons of bacterial community compositions between the samples of different ages revealed diversity indices that were significantly different between fresh and aged pellets from D-fir. Furthermore, the current study identified five unique families of bacteria that were consistently present in all fresh fecal pellet samples from D-fir but completely absent in the fecal pellet samples that were aged for certain amounts of time. In addition to serving as a basis for the characterization of the microbiome of I. minor fecal pellets, the current findings suggest multiple candidate biomarkers which may be further investigated to develop a cost-effective method to distinguish freshly produced from aged fecal pellets.

Over-the-counter (OTC) insecticide products are popular, easily available, and inexpensive do-it-yourself options for home residents. In this study, we investigated the performance of OTC insecticides consisting of bait and spray products against susceptible and field-collected strains of the German cockroach, Blattella germanica (L.) (Blattodea: Ectobiidae) using several test methods. In open arena bioassays, all OTC baits tested were ineffective on field-collected German cockroaches. The least effective OTC bait was unable to kill all test cockroaches of any strains at 14 d post-treatment. Direct spray experiments demonstrated that cockroaches treated with pyrethroid spray registered significantly shorter mean knockdown times when compared to that of the natural product. On the other hand, the natural product spray caused significantly shorter mean survival time in test insects than the pyrethroid spray (1 d). The residual efficacy of spray deposits was evaluated in the Ebeling choice box and revealed that all sprays have poor residual performance against field-collected German cockroach strains. Insecticide resistance and potential avoidance behavior may have contributed to the low performance index (PI) values of pyrethroid-based sprays, as cockroaches may have survived initial contact and subsequently avoided treated surfaces. Conversely, natural product spray deposits exhibited negative PI values for most of the study period due to spatial repellency. In general, the performance of OTC insecticide products was lower on field-collected German cockroach strains than on the susceptible strain. These products are likely ineffective at controlling the German cockroach infestations in homes.

The Pharaoh ant, Monomorium pharaonis (L.), is a widely distributed invasive tramp ant species. Due to their ability to frequently relocate nest sites when disturbed, Pharaoh ants are particularly challenging to manage. This study examined the colony movement patterns of different colony sizes of the Pharaoh ant in response to chemical disturbances caused by varying over-the-counter aerosol insecticide application rates. Three aerosol products, 3 application rates, and 4 colony sizes were tested. Essential oil-based insecticides exhibited a higher probability of inducing budding at all colony sizes when applied at a high rate. In contrast, pyrethroid-based insecticides increased the probability of inducing budding at a low application rate. The number of workers present outside the main nest in the essential oil-based insecticide-treated group decreased with increasing application rate, whereas the number of workers present outside the main nest increased in pyrethroid-based insecticide-treated groups. Furthermore, the density of workers outside the main nest appeared to play a role in influencing the final nest site after budding. The number of worker ant carcasses observed on pyrethroid-treated surfaces was significantly greater than on surfaces treated with the essential oil-based insecticide and controls. The effects of aerosol product type, colony size, and insecticide application rate on Pharaoh ant colony movement are discussed.

This study investigated the translocation of cockroach bait toxicants to the Pharaoh ant, Monomorium pharaonis (L.), through feeding on cadavers of German cockroaches, Blattella germanica (L.), which were killed by commercial gel baits. The cockroaches were first treated with 1 of 4 gel baits: Advion Trio (0.6% indoxacarb, 0.1% pyriproxyfen, 0.1% novaluron), Maxforce FC Magnum (0.05% fipronil), Alpine Rotation 1 (0.5% dinotefuran), and Vendetta Nitro (0.5% clothianidin, 0.5% pyriproxyfen) before the Pharaoh ants were allowed to forage on the cadavers. The effects of the toxicants on the Pharaoh ant colonies were examined. Ants that fed on cadavers killed by Maxforce FC Magnum showed significantly higher (P < 0.05) mortality rates among queens and brood. Advion Trio initially led to the rapid reduction of queens, workers, and brood; however, the Pharaoh ant colony later recovered as the workers abandoned treated cockroach cadavers in favor of the regular diet. Examination of the queen ovaries revealed that, in the Vendetta Nitro-treated group, the size of mature oocytes was significantly reduced (P < 0.05). However, no structural damage was observed on any oocyte, as all exhibited a visible nucleus, multiple nurse cells, and well-developed follicular epithelium. The horizontal transfer efficacy of different cockroach gel bait toxicants is discussed.

Using morphological assessments and phylogenetic inference, we described a new subterranean termite species in the genus Reticulitermes in southern California: Reticulitermes rusti sp. nov. Genetic analyses utilizing 3 mitochondrial loci (16S rRNA, COI, and COII) and 7 microsatellites successfully distinguished the new species from 2 other Reticulitermes found in southern California: R. hesperus Banks and R. tibialis Banks. Empirical measurements of key morphological characters further support the delineation of R. rusti as a new species. While R. rusti is genetically closer to R. tibialis, its soldier caste is morphologically similar to that of R. hesperus. We recommend confirming species identification by sequencing the COI or COII region. The integration of biological, genetic, and morphological data robustly supports the recognition of R. rusti as a distinct new species in southern California.

The German cockroach, Blattella germanica (L.), is a major urban insect pest primarily controlled by insecticides, including pyrethroid sprays, fipronil baits, and indoxacarb baits. However, widespread pyrethroid resistance increases the probability that cockroaches will survive treatments in the field. Many insecticides are applied concurrently or repetitively on a periodic basis, meaning survivors have the chance to be re-treated, but any lasting physiological effects from initial survival may impact the performance of subsequent treatments. We investigated the effects of sublethal deltamethrin exposure on the susceptibility of susceptible (UCR) and resistant (Ryan) strains of German cockroaches. Ineffective pyrethroid treatment was simulated by treating cockroaches with the LD20 of deltamethrin. Survivors were treated again with the same dose of deltamethrin, a food source containing the LC50 of fipronil, or a food source containing the LC50 of indoxacarb. Both strains of cockroaches experienced greater mortality when treated with deltamethrin 3 d (49.8% to 67.6%), after the sublethal exposure. No impact on fipronil or indoxacarb susceptibility was observed after pre-treatment with deltamethrin. Because surviving a deltamethrin treatment did not induce tolerance to deltamethrin or other insecticides, this suggests no within-generation drawback of current conventional management practices of applying multiple treatments in the same site. Furthermore, sequential exposure to deltamethrin caused greater mortality than expected, indicating that this insecticide may remain useful even if initial efficacy is low. Comprehensive examinations of additional resistant strains treated with formulated products are warranted to understand whether these effects may impact field control.

The brownbanded cockroach, Supella longipalpa (F.), is a cosmopolitan pest cockroach that infests indoor environments. Compared to the more prevalent German cockroach, Blattella germanica (L.), S. longipalpa has higher temperature requirements but can infest a wider range of environments within structures under suitable conditions. Little is known about the toxicity of gel baits against S. longipalpa relative to that of B. germanica. This study evaluated toxicological responses of brownbanded and the German cockroach to commercial gel baits (Advion Evolution, Maxforce FC Magnum, Maxforce Impact, Alpine, Vendetta Plus, and 1% isocycloseram) using open test arenas and Ebeling choice boxes. Results showed that gel baits were less effective against S. longipalpa. Supella longipalpa survived 3.3 to 10.2× longer than B. germanica when exposed to most bait formulations in open arenas. Gel baits showed lower performance index values against S. longipalpa than against B. germanica in choice boxes. Based on the low performance index values, it is predicted that Maxforce FC Magnum and Vendetta Plus would be ineffective in treating S. longipalpa infestations in the field. Differences in gel bait performance between the 2 species are likely due to the lower palatability of gel baits to S. longipalpa, arising from differing nutritional and moisture requirements. Correlation and regression analysis showed a direct relationship between the data obtained from both assays for S. longipalpa. While open arena bioassays are useful in comparing the toxicity of different gel baits, choice boxes replicate field conditions more closely and allow a more accurate evaluation of bait performance.

A symposium titled “Development and Application of Baits for Subterranean Termite Control in the Last Three Decades” was held from 25 to 30 August 2024, at the XXVII International Congress of Entomology in Kyoto, Japan. This event provided a platform to discuss the advancements in termite bait technologies across different regions over the past 30 years. This special collection features reports from symposium speakers, highlighting the effects of chitin synthesis inhibitor baits on termite colonies, the evolution of termite bait technology, impacts on the termite control industry in the United States and Southeast Asia, area-wide projects, and examples of innovations in bait technology.

The management of subterranean termite pests remains a major challenge in Southeast Asia, where these pests cause significant structural and economic damage. Termite baiting has emerged as an effective option to conventional soil termiticides, offering a safer pest management approach with reduced chemical input into the environment. In this paper, we review the history of termite research in Southeast Asia, highlighting the turning points of termite research, from agriculture and plantations to buildings and structures, and the transformative impact of termite baiting on the pest management industry in the region over the last 25 yr. We also discuss the outcome of a survey of pest management professionals on their baiting practices, bait performance, and reinfestation rates. All bait products eliminated termite colonies. There were significant differences in terms of the baiting period to colony elimination, with Xterm outperforming Sentricon, Exterra, and Exterminex. Above-ground (AG) baiting was preferred over in-ground (IG) baiting due to construction constraints and low IG station interception rates. While bait effectively controlled Coptotermes spp., challenges persist in managing fungus-growing termites such as Macrotermes gilvus Hagen. Reinfestation occurred in < 10% of baited premises.