Dominica Populations Research Articles

Development, application and evaluation of three novel TaqMan qPCR assays for phosphine resistance monitoring in major stored product pests Tribolium castaneum and Rhyzopertha dominica.

Stored product protection from insect pests relies heavily on the use of phosphine. The most serious drawback of phosphine is the development of resistance in major stored product insects worldwide, including the red flour beetle, Tribolium castaneum (Herbst) and the lesser grain borer, Rhyzopertha dominica (F.). Two genetic loci are responsible for phosphine resistance: the rph1 (S349G mutation in the cyt-b5-r homolog) in T. castaneum and the rph2 (P45/49S mutation in the dihydrolipoamide dehydrogenase (dld) gene) in T. castaneum and R. dominica. In this study, we have developed and applied high-throughput, practical and specific molecular diagnostics (TaqMan qPCR) for monitoring mutations S349G, P45S and P49S. In our pilot monitoring application, we have included phosphine-resistant and susceptible populations from different parts of the world (USA, Australia, Brazil) and European strains from Greece and Serbia. Our results for the resistant T. castaneum showed a P45S mutant allele frequency (MAF) of 100% and 75.0% in the populations from Serbia and Brazil, respectively. Regarding the susceptible T. castaneum, P45S was detected in Greece (MAF = 62.5%) and was absent in Australia (MAF = 0.0%). Additionally, the S349G mutation was found to be fixed in all resistant populations, while it was also detected in susceptible ones (frequencies: 65.0% and 100.0%). The only case where both mutations were fixed (100%) was a resistant population from Serbia. In R. dominica, the P49S mutation was found only in the two resistant R. dominica populations from Serbia and Greece (50.0% and 100%) and was absent from the susceptible one from Greece; thus, P49S seems to be a satisfactory indicator for monitoring phosphine resistance. Our P49S detection assay in R. dominica seems to be a viable option in this direction, yet its utilization needs additional large-scale confirmatory work. The identification of additional resistance markers also should be prioritized. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

First report of strong phosphine resistance in stored grain insects in a far northern tropical region of Australia, combining conventional and genetic diagnostics

Although phosphine resistance monitoring and management programs are well advanced in Australia, the tropical northern part of the continent has received little attention. To address this, grain storages were sampled in the Townsville region in the Burdekin river catchment area of northern Queensland, and insect populations were subjected to resistance testing. Sampling of storages including silos, food processing facilities and feedlots was carried out during July to August 2019 and February to March 2020. Of the several species collected, populations of two major pest species, Rhyzopertha dominica and Tribolium castaneum were subjected to phenotypic resistance and molecular screening using discriminating doses and gene specific DNA marker, respectively. Utilising phenotypic assay, of the 17 populations of R. dominica, 12 were diagnosed as weakly resistant and five as strongly resistant; whereas of the 34 populations of T. castaneum, two were found to be susceptible to phosphine, 15 were determined as weakly resistant and 17 as strongly resistant. The molecular diagnostics, however, determined rph2 alleles for strong resistance in some populations each of R. dominica and T. castaneum that were diagnosed as weakly resistant in the phenotypic assay. The most prevalent rph2 alleles were found to be P49S and K142E in R. dominica populations and P45S and G131S in T. castaneum populations. Our results highlight the need of more comprehensive study towards determining the level of pests and resistance risks in this region.

Repellency of Ferulago angulata (Schlecht.) Boiss essential oil on two major stored-product insect pests without effect on wheat germination

There has been an increasing demand among agricultural researchers and producers for bio-insecticides due to the threats of the related chemicals leading to human health problems, environmental contamination, pest resistance, and secondary pest outbreaks. In this regard, the repellent effects of the essential oil extracted from Ferulago angulata (Schlecht.) Boiss as a well-known medicinal plant were measured against the red flour beetle (Tribolium castaneum (Herbst)) and lesser grain borer (Rhyzopertha dominica (F.)) using the three different techniques of filter paper, leaky glass, and olfactometry. The experiments were conducted at the concentrations of 30, 52, 93, 165, and 300 ppm under controllable conditions. The maximum Percent Repellency (PR) rates of the essential oil at the concentration of 300 ppm were found to be 59.01, 54.12, and 43.21% for T. castaneum and 48.84, 50.52, and 42.73% for R. dominica based on the mentioned methods, respectively. By enhancing the essential oil concentrations and exposure times, the PR rates increased. Furthermore, the essential oil effects of F. angulata on wheat germination were evaluated and no decreases in the germination of the treated wheat seeds were found at the tested concentrations. According to the results of the present study, the essential oil of F. angulata could be used for reducing T. castaneum and R. dominica populations.

High‐dose strategies for managing phosphine‐resistant populations of Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae)

Rhyzopertha dominica is a serious pest of stored grains and many populations have resistance to the fumigant phosphine. Some populations contain beetles with a 'strong resistance' phenotype. Recent work found the LC50 values for two strong-resistant populations recently studied in North America, Belle Glade and Minneapolis were 100- and 595-fold higher, respectively, compared to LC50 of a lab-susceptible strain. Populations with 'weak-resistant' phenotypes had LC50 values 5- to 10-fold that of a susceptible strain. The work reported below aimed to determine the minimum phosphine concentrations and number of days of exposure needed to effectively control all life stages of representative weak- and strong-resistant strains, and then to recommend the treatment conditions needed to control strongly phosphine-resistant R. dominica in pest populations. A dose-mortality assay estimated that phosphine fumigation over 48 h using 730-870 ppm at 25°C would control adults of both strongly resistant R. dominica populations. Fumigations with mixed life stage cultures found 200 ppm killed all susceptible and weak-resistant beetles in 2 days, but the strong-resistant Minneapolis and Belle Glade strains had substantial survivors at 200 ppm. Furthermore, the Belle Glade strain had beetles that survived 1000 ppm in 2-day fumigations. The strong-resistant Belle Glade strain needed nearly 10 days at over 400 ppm to have acceptable levels of control. This study recommends protocols to manage strongly resistant R. dominica populations provided that a minimum phosphine concentration of 400 ppm be maintained at 25°C or higher for up to 10 days. © 2019 Society of Chemical Industry.

A high-throughput system used to determine frequency and distribution of phosphine resistance across large geographical regions.

Next-generation sequencing can enable genetic surveys of large numbers of individuals. We developed a genotyping-by-sequencing assay for detecting strong phosphine resistance alleles in the dihydrolipoamide dehydrogenase (dld) gene of Rhyzopertha dominica populations. The assay can estimate the distribution and frequency of resistance variants in thousands of individual insects in a single run. We analysed 1435 individual insects collected over a 1-year period from 59 grain-storage sites including farms (n=29) and central storages (n=30) across eastern Australia. Resistance alleles were detected in 49% of samples, 38% of farms and 60% of central storages. Although multiple alleles were detected, only two resistance variants (P49S and K142E) were widespread and each appeared to have a distinct but overlapping geographical distribution. The type of structure in which the grain is stored had a strong effect on resistance allele frequency. We observed higher frequencies of resistance alleles in bunker storages at central sites compared with other storage types. This contributed to the higher frequencies of resistance alleles in bulk-handling facilities relative to farms. The discovery of a storage structure that predisposes insects to resistance highlights the utility of our high-throughput assay system for improvement of phosphine resistance management practices. © 2018 Society of Chemical Industry.

Detection and quantification of the insect pest Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae) in rice by qPCR

The early detection of insects during grain storage and processing remains a major issue for the cereal industry, especially when immature stages are hidden inside the grain kernels. For this reason, we developed a qPCR method to detect and quantify one of the main pests of stored products in rice: the coleopteran internal feeder Rhyzopertha dominica. For that purpose, a specific primer set was designed to amplify artificial infestations of this pest in rice. Then, using a regression model, a standard curve was generated that correlated individuals to adult equivalent DNA quantity (inverse of the Ct value). Results revealed that the designed primer set was specific for R. dominica when tested against the other 4 common internal feeders in grain. The technique showed to be accurated (DNA was detected in more than 73% of the samples) and sensitive to insect presence (i.e. from 0.02 adults, 0.1 3rd instar to pupae or 13 egg to 2nd instar detectable per kg of rice). Moreover, the detection of R. dominica was strongly associated with a given infestation size: DNA quantity increased along with the size of the population. The use of the described qPCR protocol in grain and milling factories may enhace the critical detection and quantification of R. dominica populations in raw materials and processed food.

Base-line susceptibility of field populations of Rhyzopertha dominica (F.) to spinosad in Australia

Spinosad has recently been registered in several countries for long-term protection against a range of stored grain insects including the lesser grain borer, Rhyzopertha dominica (F.). The potential for development of resistance to spinosad is demonstrated by the existence of resistance in many insect pests of agriculture. The aim of this study was to determine the base-line susceptibility of R. dominica to spinosad, to provide a basis for future resistance monitoring. Eighteen insect populations of R. dominica were collected from field storage sites across four States within Australia, and exposed to a range of spinosad rates, including its current registered rate of 1 mg kg−1 (1 ppm). Base-line susceptibility was assessed based on adult mortality and production of F1 adults. Comparison of LC50 and LC99.9 indicated the existence of low level of variation among the tested R. dominica populations, in their susceptibility to spinosad. For adults, there was a narrow range of LC50 values with the highest (0.027 ppm) being 2.5 × the lowest (0.011 mg kg−1). Similarly, LC99.9 values showed a narrow range with the highest (0.36 mg kg−1) being 3.6 × the lowest (0.10 mg kg−1). For adult progeny produced in spinosad treated grain, there was a narrow range of LC50 values with the highest (0.025 mg kg−1) being 5 × the lowest (0.004 mg kg−1) and the highest LC99.9 values (0.67 mg kg−1) being 5 × the lowest LC99.9 (0.13 mg kg−1). Based on the data generated from this study, we recommend a dose of 1 mg kg−1(1 ppm) to be used to discriminate between susceptible and resistant populations for future resistance monitoring programs.

Flight of Rhyzopertha dominica (Coleoptera: Bostrichidae)-a Spatio-Temporal Analysis With Pheromone Trapping and Population Genetics.

The flight of the lesser grain borer, Rhyzopertha dominica (F.), near grain storages and at distances from them, was investigated to assess the potential of these beetles to infest grain and spread insecticide resistance genes. We caught R. dominica in pheromone-baited flight traps (and blank controls) set at storages, in fields away from storages, and in native vegetation across a 12-mo period. A functional set of highly polymorphic microsatellite markers was developed, enabling population genetic analyses on the trapped beetles. Pheromone-baited traps caught just as many R. dominica adults at least 1 km from grain storages as were caught adjacent to grain storages. Samples of beetles caught were genetically homogeneous across the study area (over 7,000 km2) in South Queensland, Australia. However, a change in genetic structure was detected at one bulk storage site. Subsequent analysis detected a heterozygous excess, which indicated a population bottleneck. Only a few beetles were caught during the winter months of June and July. To assess the mating status and potential fecundity of dispersing R. dominica females, we captured beetles as they left grain storages and quantified offspring production and life span in the laboratory. Nearly all (95%) of these dispersing females had mated and these produced an average of 242 offspring. We demonstrated that R. dominica populations in the study area display a high degree of connectivity and this is a result of the active dispersal of mated individuals of high potential fecundity.

Assessment of Fitness Effects Associated with Phosphine Resistance inRhyzopertha dominica(F.) (Coleoptera: Bostrichidae) andTribolium castaneum(Herbst) (Coleoptera: Tenebrionidae)

Phosphine-resistant populations of lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae) and red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) were reported in Oklahoma, U.S.A. in 2012. Knowledge of the fitness effects associated with phosphine resistance is important for the development of resistance management strategies. Therefore, the goal of our study was to determine if there were fitness effects associated with phosphine resistance in populations of R. dominica and T. castaneum from Oklahoma. We measured population growth and developmental rates of phosphine-resistant and -susceptible populations of these two species in a phosphine-free environment. Three resistant R. dominica populations exhibited lower population growth and developmental rates compared to the susceptible population, whereas the only resistant T. castaneum population tested exhibited higher population growth and developmental rates compared to the susceptible population. Our data indicate that there is a fitness cost and possibly a fitness benefit, respectively, associated with phosphine resistance genes in these two species. In conclusion, phosphine resistance development in susceptible R. dominica populations can presumably be slowed by infrequent use of phosphine, whereas it can be mitigated by suspending phosphine use for extended periods of time in resistant populations. However, withholding phosphine use for long periods of time may not mitigate phosphine resistance in T. castaneum.

Susceptibility of field populations of the lesser grain borer, Rhyzopertha dominica (F.), to deltamethrin and spinosad on paddy rice in Taiwan

The lesser grain borer, Rhyzopertha dominica (F.), a primary pest of paddy rice in Taiwan, attacks undamaged grains, and induces secondary infestation by other pests. In the past decade, a pyrethroid, deltamethrin, has been commonly used to control this pest, and the development of insect resistance to this insecticide has recently become a major concern. In this study, the susceptibility of R. dominica to deltamethrin and the potential alternative insecticide, spinosad, was investigated in a range of field samples collected from across Taiwan and tested in treated grain bioassays. The deltamethrin bioassays revealed that the most tolerant R. dominica population collected from Nantou county (Nantou population) was 63.8 times harder to kill than the least tolerant Yangmei population. The bioassays with spinosad revealed that the most tolerant Minshong population was 2.7 times harder to kill than the least tolerant Liujia population, and there was no significant difference in susceptibility to spinosad among all 16 population samples tested. The occurrence of higher deltamethrin LC50 values for central, southern, and eastern R. dominica populations suggests that the selection of new alternative insecticides is essential for controlling this species. Spinosad was found to be effective without cross-resistance to deltamethrin, and could thus be a potential alternative. Alternating deltamethrin with spinosad or combinations of deltamethrin and spinosad may slow the development of resistance to these grain protectants.

Geostatistical analysis of adult Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae) in wheat stored at constant temperatures

Insect monitoring and sampling programmes are used in the stored grains industry for the detection and estimation of insect pests. At the low pest densities dictated by economic and commercial requirements, the accuracy of both detection and abundance estimates can be influenced by variations in the spatial structure of pest populations over short distances. Geostatistical analysis of Rhyzopertha dominica populations in 2-dimensions showed that, in both the horizontal and vertical directions and at all temperatures examined, insect numbers were positively correlated over short (0–5 cm) distances, and negatively correlated over longer (≥10 cm) distances. Analysis in 3 dimensions showed a similar pattern, with positive correlations over short distances and negative correlations at longer distances. At 35 °C, insects were located significantly further from the grain surface than at 25 and 30 °C. Dispersion metrics showed statistically significant aggregation in all cases. This is the first research using small sample units, high sampling intensities, and a range of temperatures, to show spatial structuring of R. dominica populations over short distances. This research will have significant implications for sampling in the stored grains industry.

Phosphine resistance in Rhyzopertha dominica (Fabricius) (Coleoptera: Bostrichidae) from different geographical populations in China

This study was carried out to determine the level of phosphine resistance in 16 Rhyzopertha dominica (Fabricius) populations that were collected from ten provinces and one municipality in China following the Food and Agriculture Organization’s (FAO) standard method. Results showed that the 50% lethal concentration (LC50) of phosphine to these R. dominica populations ranged from 0.017 to 4.272 mg/L. Of the 16 populations, 5 were of low resistance, 6 were moderately resistant, and 5 were high resistant. The instantaneous rate of population increase (ri) was correlated with phosphine resistance followed by the Exponential model (y = 0.037e -0.005X , R 2 = 0.937). The relationship between the types of grain storage

Genetic Diversity among different Geographical Population of Rhyzopertha dominica in China as revealed by AFLP (Coleoptera: Bostrichidae

Rhyzopertha dominica (Fabricius 1792) is one of the major coleopterous pests of stored products in China and around the world. It causes serious losses to stored grains. In this study, the genetic diversity and structure of 13 populations (97 individuals) of R dominica were examined using Amplified Fragment Length Polymorphism (AFLP) analysis. Four primer combinations were selected to identify a total of 128 polymorphic loci ranging from 50 to 450 bp. The percentage of polymorphic loci (Pp) was 51.88 % at the population level and 84.87 % at the species level, respectively. Nei's gene diversity (h) and Shannon's Information index (I) had similar trend with the percentage of polymorphism. Thus, the estimated genetic diversity using these three indicators revealed a high level of genetic variation within each R. dominica population. At the species level, Analysis of Molecular Variance (AMOVA) revealed a significantly greater genetic variation within populations (81.11 %) than among populations (18.89 %). The Mantel test of isolation by distance revealed that there was no significant correlation between Nei's genetic distance and geographical distance (Lg) among all populations (r = 0.20787, P = 0.0519 > 0.05). A Neighbour Joining dendrogram based on Nei's unbiased genetic distance revealed four distinct groups that did not correspond to the geographical regions. This result suggests that isolation by distance does not describe the pattern of gene flow among R. dominica populations. How different ecology of grain storage area and depot type could influence R. dominica population genetic structure were also discussed.

Survival and reproduction of lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae) on flora associated with native habitats in Kansas

Capture of Rhyzopertha dominica in pheromone-baited traps located many kilometers away from grain storage suggests that this species may be exploiting non-grain food sources. To investigate the potential for survival of this species on alternative hosts in the absence of grain, we conducted no-choice feeding assays with twigs and seeds of trees, and seeds of grasses, forbs, and shrubs, commonly encountered on Kansas prairie landscapes where R. dominica has been captured. In addition, R. dominica development and progeny production were assessed on seeds that adults were able to survive on for at least two weeks. Adult survival was poor on grass and forb seeds, although 13.4% of individuals survived on Elymus canadensis, Canada wildrye, seeds after two weeks, compared with 80.3% on Triticum aestivum, wheat, and 0.0% survival in the absence of food. Beetles readily tunneled into twigs from a wide range of tree species, but survival was generally low. A few individuals survived up to four weeks on Gleditsia triacanthos, honey locust. In contrast, bioassays showed that R. dominica could survive and reproduce on damaged seeds (acorns) of six species of oak, but not on undamaged seeds. For example, survival was 95.8% on damaged Quercus muehlenbergii, chinquapin oak. A survey of acorns at the original field collection site showed that the majority of the acorns on the ground had been cracked or bored into by insects and small mammals. Furthermore, we recovered three R. dominica adults from acorns collected in the field and held in sealed containers in the laboratory. These findings suggest that R. dominica populations in Kansas can persist on wild acorns when grain is not available.

α-Amylase Activity of <I>Rhyzopertha dominica</I> (Coleoptera: Bostrichidae) Reared on Several Wheat Varieties and Its Inhibition with Kernel Extracts

Total progeny of Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae) reared on 10 wheat, Triticum aestivum L., varieties was evaluated. Higher amylase activities were detected in populations with few individuals, whereas the opposite was observed in higher populations. As protein ingested increased, reproductive success increased. However, consumption of wheat protein was inversely correlated with amylase activity levels (r = -0.66). Amylase activity in homogenates of R. dominica populations showed variable inhibition by wheat extracts prepared from wheat varieties on which they were reared. Insect populations with lowest amylase activities were inhibited more by wheat extracts than those with higher amylase activity (r = -0.77). An electrophoretic analysis revealed four phenotypes showing combinations of three isoamylases (Rm 0.70, 0.79, and 0.90) in different populations of R. dominica. Some of the insect progeny that emerged from resistant wheat varieties contained the three isoamylases, whereas progeny that emerged from the most susceptible varieties showed reduced activity of isoamylases 0.70 or 0.90. These results suggest that the alpha-amylase activity levels and the composition of isoamylases in R. dominica populations are modulated by diet and that the alpha-amylase inhibitory activity of the wheat kernels influences these variations.

Allozyme variation among Brazilian and U.S. populations of Rhyzopertha dominica resistant to insecticides

AbstractThe lesser grain borer (Rhyzopertha dominica (F.)) is an important pest of stored grain in many parts of the world (Paleartic, Ethiopian, Oriental, Australian, Neotropical, and Neartic regions) with the ability to fly long distances. These insects have been shown to be resistant to organophosphorus insecticides in several studies. Polyacrylamide gel electrophoresis was used to assess the genetic variability within and among eight Brazilian and seven United States populations of R. dominica and to determine how insecticide resistance may be spreading within both countries. Significant variation in allele frequency among populations was observed at all six polymorphic enzyme loci that were examined. The Brazilian and U.S. populations were genetically differentiated from one another; populations within the U.S. and those within Brazil were also differentiated from one another. The mean genetic similarity among the seven U.S. populations collected in a small region in northeast Kansas was smaller than that among eight Brazilian populations collected in a relatively large geographical area. These results are consistent with the resistance ratios to chlorpyriphos‐methyl in R. dominica populations from Brazil and the U.S. and the information available concerning patterns of flight activity in this insect.

Suppression of Beetles in Stored Wheat by Augmentative Releases of Parasitic Wasps

Field studies were conducted to assess the effectiveness of the parasitoid wasps, Cephalonomia waterstoni (Gahan), and Choetospila elegans (Westwood), for controlling Cryptolestes ferrugineus (Stephens), rusty grain beetle and Rhyzopertha dominica (F.), lesser grain borer. On 6 July 1993 and 7 July 1994, adults of both C. ferrugineus and R. dominica were released at monthly intervals into 6 steel grain bins each containing 27.2 t of hard red winter wheat, Triticum aestivum L. Adults of both parasitoid species were released into 3 of the bins 21 d after the 1st beetle release. The amount of suppression of C.ferrugineus by C. waterstoni could not be measured in either year of this study because C. waterstoni infested the control bins. However, C. elegans was effective in suppressing R. dominica populations. In 1993 and 1994, R. dominica populations were suppressed by 98 and 91% compared with the control bins. After 198 d from initial beetle release in 1993, the treatment bins averaged 0.05 R. dominica per kilogram and the control bins averaged 2.06 R. dominica per kilogram. After 131 d from initial beetle release in 1994, the treatment bins averaged 6.94 R. dominica per kilogram and the control bins averaged 81.03 R. dominica per kilogram.

Survival of Rhyzopertha dominica (Coleoptera: Bostrichidae) in Stored Wheat Under Fall and Winter Temperature Conditions

Cold temperature survivorship of Rhyzopertha dominica (F.) populations with a natural age structure in stored wheat was estimated for a natural fall cooling rate of 2 degrees C per week and winter temperatures of 17, 13, 9, and 5 degrees C. Logistic equations were fitted to the data to predict the survivorships of the adults outside kernels and immatures and preemergent adults inside kernels as a function of exposure time over the 5-17 degrees C temperature range. During the acclimation period, many insects died, and roughly 80, 55, and 25% of the insects were alive after temperatures had decreased at a rate of 2 degrees C per week from 17 degrees C to 13, 9, and 5 degrees C, respectively. At the end of cold temperature exposure period, many R. dominica survived at 17 degrees C, a few at 13 degrees C, but none at 5 or 9 degrees C. The colder the temperature the more rapidly survivorship decreased. The mostly immature insect population inside kernels was killed less rapidly than the external adult population at 5 and 9 degrees C and more rapidly at 13 and 17 degrees C. Daily survival rates decreased and then increased again indicating that those insects surviving short exposures to cold temperatures had a greater chance of surviving long exposures to cold temperatures. These equations will help extend our population model to predict the survival of R. dominica populations in stored wheat through the winter.

Small bin trials to determine the effectiveness of acid-activated kaolin against four species of beetles infesting paddy under tropical storage conditions

Control of populations of Rhyzopertha dominica, Sitophilus oryzae, Tribolium castaneum and Oryzaephilus surinamensis infesting paddy treated with acid-activated kaolin (AAK) at 0.75% w/w or with pirimiphos-methyl (PM) diluted with AAK to give 2 mg PM/kg paddy was compared with that in untreated paddy or paddy admixed with a 2% PM dust formulation on talc at 8 mg a.i./kg. Grain was stored in 45 kg lots in fibreboard drums for 250 days and subjected to periodic infestation with the beetles. All three treatments controlled adult populations of the insects up to 200 days post-treatment, but R. dominica populations started to increase at 250 days in the treatment using 2% PM dust, and this treatment gave progressively lower mortality of R. dominica and less suppression of progeny development in 7 day bioassays using samples taken through the trial than the other treatments. Mean % breakdown of PM formulated on AAK was about twice that on untreated kaolin in accelerated storage tests, and PM residues declined at a faster rate in paddy treated with the mixed dust formulations of AAK and PM than in paddy treated with the 2% PM dust formulation. The deactivator diethylene glycol could be incorporated at up to 10% w/w in AAK with negligible effect on the insecticidal activity of the dust to R. dominica.