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The rice weevil, Sitophilus oryzae (L.) (Curculionidae), is a globally distributed pest of stored grain, but despite having functional wings it is considered a reluctant flier. An analysis of the population genetics of S. oryzae from all major regions in Australia where grain is grown and stored in bulk revealed limited population structure nationally, despite our expectation that the low levels of flight in this species would impose considerable population structure geographically. Little genetic structure detected in nuclear DNA yet strong mitochondrial DNA structure was found among populations within the growing regions suggesting greater dispersal in males than females. Also, there were low levels of mitochondrial DNA diversity within and among Australian S. oryzae populations. Anthropogenic movement is most likely the reason for the observed lack of isolation-by-distance pattern of gene flow, especially in eastern Australia. The extent of gene flow demonstrated in our study has potential implications for the development and spread of phosphine resistance in Australia. Undoubtedly, selection for phosphine resistance in S. oryzae is occurring in all grain growing regions because of the widespread use of phosphine fumigation, but the level of gene flow demonstrated in Australian S. oryzae suggests that we can expect some spread of resistant insects geographically despite the apparent limited flight in this species.

To better understand the field ecology of stored grain beetles in southern Australia we monitored the flight activity of Rhyzopertha dominica (F.) and Tribolium castaneum (Herbst) over a 2 year period. We used target-specific pheromone lures and Lindgren funnel traps in open fields, at grain storages, and in remnant native vegetation. Over 35,000 R. dominica and 2,500 T. castaneum were caught. Significantly more R. dominica (46.4%) were caught in areas of remnant vegetation than at storage sites (29.2%) or in open fields (24.4%), suggesting this species may be utilising non-grain food sources in some areas. In contrast, the majority of T. castaneum (45.4%) were caught adjacent to storages. An intense summer heatwave (14 day mean maximum air temperature 41.9 °C) corresponded to captures of both species declining to near zero until the following spring. Sex ratios of both species varied significantly over time but were unaffected by habitat type. Two mark/release/recapture (MRR) trials using laboratory-reared R. dominica were conducted using a 1 km trap array and pheromone lures. The recovery rate for marked beetles in the first trial was 1.41%, however a subsequent experiment comparing fresh and weathered lures showed that lure attractancy declines to 50% between 3 and 4 days after deployment during hot weather (mean daily maximum air temperature 29.4 °C). When the MRR trial was repeated with lures replaced at shorter (2 day) intervals, the recovery rate rose to 3.27% and the number of wild R. dominica captured increased proportionately. The short half-life of rubber septum-based R. dominica pheromone lures needs to be considered when designing surveillance programs, particularly if attempts are being made to correlate R. dominica dispersal patterns to short-term weather events.

This Best Management Practices guide presents Queensland’s pulse industry research-based advice for optimising post-harvest storage, including detailed recommendations for hygiene, aeration and fumigation. It is just one of many research outputs that align with our objective to enhance the productivity, profitability and sustainability of value chains through improved practices, innovation and technology. Optimum storage is critical to maximise profitability and sustain Australia’s reputation in a highly competitive international market through supply of premium quality, insect-free pulses.

Rhyzopertha dominica and Tribolium castaneum are key pests of stored grains globally. These two species often occur together in infestations, and are seldom found outside the agricultural environment. Understanding the movement of these beetle pests is crucial for the development of management strategies, in particular to prevent the spread of phosphine resistance, which is a serious issue in many countries. We sampled both of these beetle species from farm silos across Australia, and used microsatellite markers to assess whether these two pests sharing the same resource show similar patterns of genetic diversity and genetic structure. Both species had high levels of genetic diversity, and showed some evidence of genetic structure across Australia, but the patterns of genetic structure differed across the two species. Specifically, our results suggest that there is significant gene flow in T. castaneum across Australia, with the clear isolation-by-distance pattern indicating that active flight may play an important role in determining genetic structure in this species. The significant movement of T. castaneum beetles across Australia will likely result in the continued spread of phosphine resistance alleles across Australia, leading to increased incidence of strongly resistance populations. Less gene flow was evident in R. dominica, suggesting movement of these beetles among localities is more restricted. Our results demonstrate that pests mostly sharing the same resources can significantly differ in their genetic structure and genetic diversity, suggesting species-specific management practices are essential.

The bruchid, Callosobruchus maculatus F., commonly known as the cowpea weevil, infests stored mungbean and other legumes. Aeration cooling has potential as a non-chemical means of managing this species in stored legumes. Population growth of C. maculatus in mungbean was investigated at nine constant temperatures (15, 17.5, 20, 22.5, 25, 27.5, 30, 32.5 and 35 °C) at 60% RH so that a target temperature for cooling could be estimated. We used two laboratory strains: Strain 1 and Strain 2 that had been in culture for 16–17 years and 1–2 years respectively. The results for the two strains were very similar. Egg to adult development occurred between 20 and 35 °C for Strain 1 and 17.5 and 35 °C for Strain 2. The optimal temperature for population growth was estimated to be 32.2 and 33.7 °C for Strains 1 and 2, respectively. The estimated lower threshold for population growth, i.e. the temperature at which population growth is zero, was 17.5 °C for Strain 1 compared with 17.1 °C for Strain 2. Based on our results, we recommend a target temperature of 17 °C for aeration cooling to manage C. maculatus infestations in mungbean during storage.

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.

Studies of insect movement are hampered by the small size of insects and the associated difficulty in tracking them in the environment. We tested the potential of quantum dots (QDs) to mark large numbers of insects very quickly. Our results demonstrate that green CdTe (cadmium tellurium) QDs were effective markers in the laboratory and can be applied to large numbers of insects very easily. Successful recaptures in the field demonstrate that QDs have great potential as external markers.

The lesser grain borer, Rhyzopertha dominica, and the rust red flour beetle, Tribolium castaneum, are two major beetle pests commonly found infesting stored products worldwide. Both species can cause severe economic damage and their management is complicated by their potential to develop resistance to several of the limited chemical options available. However, pest management strategies can be improved by understanding the ecology of the pest insect. To determine the spatiotemporal activity of R. dominica and T. castaneum, we conducted a trapping study over two years in a temperate region of south-eastern Australia, with traps located near grain storages and fields. We captured higher numbers of R. dominica than T. castaneum, and both species were more prevalent in traps located close to grain storages. Similar and consistent seasonal patterns were displayed by both species with activity ceasing during the winter (June-August) months. We found linear correlations between maximum daily temperatures and trap catches, and minimum threshold temperatures for flight activity were 14.5 °C and 15.6 °C for R. dominica and T. castaneum, respectively. The results are discussed in relation to the ecology of these pests along with their implications for pest management.

Resistance in pest insects to the grain fumigant phosphine (PH3) poses a threat to trade and food security. The possible pleiotropic effects of PH3 resistance on development and reproduction were investigated in the red flour beetle, Tribolium castaneum (Herbst), by introgressing two genes known to be major contributors to strong resistance (tc_rph1 and tc_rph2) into a susceptible background. The tc_rph2 allele was the G135S variant, whereas the identity of tc_rph1 allele was unknown but could have been one of the three known variants (L119W, V123F, or S349G). The introgressed resistant strain was 288× more resistant than the susceptible strain, based on mortality after a 20 h fumigation with PH3. Molecular screening confirmed that the introgressed strain was homozygous for the resistance genes, but was otherwise indistinguishable from the susceptible strain based on screening with 12 neutral DNA markers. We found no differences of consequence in developmental time between the susceptible and introgressed resistant strains. Similarly, the number of F1 adults produced by these strains was more or less equal, as was the weight of individual F1 adults. The conclusions remained the same regardless of whether the experiments were conducted on a flour-based medium or wheat. Thus, we found no evidence that being fully strongly PH3 resistant (i.e., homozygous for tc_rph1 and tc_rph2) has major consequences in terms of development or reproduction in T. castaneum.

Development of resistance in major grain insect pest species to the key fumigant phosphine (hydrogen phosphide) across the globe has put the viability and sustainability of phosphine in jeopardy. The resistance problem has been aggravated over the past two decades, due mostly to the lack of suitable alternatives matching the major attributes of phosphine, including its low price, ease of application, proven effectiveness against a broad pest spectrum, compatibility with most storage conditions, and international acceptance as a residue-free treatment. In this review, we critically analyze the published literature in the area of phosphine resistance with special emphasis on the methods available for detection of resistance, the genetic basis of resistance development, key management strategies, and research gaps that need to be addressed.

The reasons for Tribolium castaneum undertaking dispersal flight in the field are poorly known. The research reported here was designed to test, in the field, the predictions generated from our previous laboratory study about the dispersal flight of T. castaneum beetles. The results of that laboratory study suggested that younger beetles with large bodies and higher fat content tend to fly more frequently, and female flyers are likely to live longer with a higher lifetime fecundity relative to those beetles that remain. These predictions were tested by sampling beetles flying within storage and at various distances (20 and 300 m) from a large population infesting stored cotton seed. Beetles were also collected directly from the infested cotton seed as a representation of ‘resident beetles’. Of the adults collected, a subset was weighed and measured, and others were tested for their fecundity, fat content and lipofuscin levels. The survival and total fecundity of females (until day 105 post-emigration) was statistically similar across the treatments, but access to males later in life (i.e. after day 105), to a subset of females from each treatment, increased their fecundity (except for those trapped at 300 m). The majority of females that were caught dispersing are presumed to be relatively young, multiply mated, and produced numerous offspring (mean = 307.3) in the absence of males. Fat content was significantly higher across flying beetles (both sexes) trapped at 2 m (within the shed) compared to flying beetles trapped at longer distances. Flight propensity was evidently not influenced by sex, weight or body size. The lipofuscin intensities of flyers was generally significantly higher than those of resident males and females, although a reliable estimate of their age would add significant value to spatio-temporal studies in these beetles. These findings have implications for management of phosphine resistance.

Cryptolestes ferrugineus is a common beetle pest of stored grain for which techniques to monitor dispersing beetles are limited. Early research found several male-produced aggregation pheromones, but there has been little related work since that time. This paper reports experiments on orientation of C. ferrugineus in response to synthetic pheromones and other semiochemicals via flight and walking. Field trapping studies showed that flying beetles were caught on the western sides of grain bins in Kansas compared to the other three cardinal directions. Work with synthetic formulations of the two male-produced aggregation pheromones found that flying beetles were attracted to traps with the pheromone and wheat compared to traps with wheat only. Walking bioassays in the laboratory determined that either of the two aggregation pheromones, known as Cucujolide I and Cucujolide II, were attractive whether deployed singly or in combination. Laboratory bioassays showed that volatiles from grains, other grain-based materials and two commercial food attractants used in traps were attractive to C. ferrugineus. Further laboratory assays demonstrated that C. ferrugineus would orient to synthetic pheromones of three other beetle species and one moth species, all common pests of stored products. These new data on semiochemicals for C. ferrugineus suggest future work that could be done toward developing new tools for detecting and monitoring this serious pest.

An understanding of how sublethal exposure to phosphine affects an organism’s respiration is important for predicting its effects on activities depending on a reliable energy source including movement. After treatment with the appropriate sublethal doses of phosphine (LC10), both resistant and susceptible Tribolium castaneum beetles suffered reductions in respiration rates, flight initiation rates and successful location (by walking) of aggregation pheromone lures. The susceptible beetles showed a significantly greater reduction in their respiration rate (53.5%) after exposure to sublethal doses of phosphine compared to the resistant beetles (37.5%), although the respiration rate was still higher in susceptible beetles than in resistant ones. Simultaneously, much larger decreases in the activities associated with both walking and flight were observed in the susceptible beetles, after exposure to sublethal doses of phosphine, compared to the decreases recorded in resistant beetles. The relatively greater reduction in the locomotory responses of susceptible beetles showed that these insects may withstand exposure to phosphine by remaining relatively still and reducing their respiration rate. They would thus minimize their exposure to phosphine, but perhaps only incidentally because the lack of movement may be the result of impairment. By contrast, phosphine-resistant beetles, when exposed to phosphine fumigation, continue to move and may even remove themselves from areas of phosphine exposure. An understanding of how the survivors of sublethal exposures behave is important for predicting the spread and local build-up of phosphine resistance genes and thus improving the control and resistance management of stored grain pests.

A key component in the management of resistance to fumigant phosphine in stored products pests is their early detection and implementation of control strategies. Currently, resistance testing involves exposing adults to a specific discriminating concentration over a fixed time period (20–48 h). Although it is widely adopted, this test takes significant time for assay preparation (up to 4 wk) as well as diagnosis (1–2 wk). To address these lacunae, we have established a ‘quick knockdown test’ using a key grain insect pest, rice weevil, Sitophilus oryzae (L.). Susceptible, weakly and strongly phosphine-resistant reference strains were exposed to a threshold concentration of phosphine over short exposure periods (min to h). The time to knockdown (KT) responses to phosphine were characterized at 2 (1,440 ppm) and 5 mg/liter (3,600 ppm). The time to 99.9% KT (KT99.9) at 2 mg/liter was 12.52 min for the susceptible adults, compared with 167.9 and 1,510 min in the case of weakly and strongly resistant phenotypes, respectively. As anticipated, increasing the concentration of phosphine to 5 mg/liter halved the KT99.9 (81.57 min) to separate weakly and strongly resistant populations than it was required at 2 mg/liter. We validated the KT99.9 value for the 5 mg/liter against field-derived populations of S. oryzae. The results were aligned with the existing Food and Agriculture Organization approach, confirming that the proposed ‘quick test’ is a reliable tool to rapidly diagnose resistance in this species.

The pyrethroid, deltamethrin, is currently used as a grain protectant to protect stored grain from insect pests in several countries including Australia. We examined the variation in response to wheat treated with deltamethrin among 15 field populations of the lesser grain borer, Rhyzopertha dominica (F.) collected from Queensland and New South Wales in eastern Australia during 2008 and 2009, to establish whether resistance has developed in this species. Based on the results of treated wheat bioassays, using a discriminating dose of 0.5 mg kg−1, we found that 14 of the 15 field populations were resistant to deltamethrin. The distance between the two most geographically separated field populations was 450 km, and both of these populations contained resistant insects. Deltamethrin applied at 1 mg kg−1 alone or with the synergist piperonyl butoxide at 8 mg kg−1 failed to control resistant R. dominica. On the basis of our findings, we conclude that populations with deltamethrin resistant individuals are common in the eastern part of Australia, and control failures are expected when such populations are present in treated grain.

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.

Many studies have been published on the flight activity of stored grain beetles in temperate regions, but few have focussed on tropical and sub-tropical regions. The spatio-temporal patterns of flight activity of Tribolium castaneum (Herbst) and Rhyzopertha dominica (F.) were quantified in a grain growing district on the Tropic of Capricorn in central Queensland, Australia. Nine traps baited with aggregation pheromone lures were monitored at 2-wk intervals (fortnightly) for 1 year along a 28.4 km linear transect that included sites at bulk grain depots and sites away from stored grain. Beetles of both species were trapped every fortnight during the study. The spatio-temporal patterns of flight activity differed greatly across the two species, as predicted from studies elsewhere. Rhyzopertha dominica was widespread across the landscape, as the mean trap catch of this species was equal in depot and non-depot traps. In contrast, T. castaneum was more frequently trapped in depot traps than non-depot traps during the colder months, but was much more widespread across the landscape during the summer months. Tribolium castaneum also showed a clear mid-summer peak in flight activity, whereas R. dominica flight activity was highly variable throughout the study. In general, our results reveal patterns that are consistent with those found for T. castaneum and R. dominica in southern Queensland. The contrasting spatio-temporal patterns of flight activity of R. dominica and T. castaneum show that species-specific approaches may be needed to manage these pests and that the spatio-temporal dynamics of resistance genes may differ across these species.

Resistance to the fumigant phosphine has been demonstrated to impact on the dispersal abilities of the stored product pest Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae). A series of behavioural bioassays were conducted in a wind tunnel to further investigate whether the fitness consequences of phosphine resistance on flight propensity and resource localisation could be influenced by attractive odours or individual factors such as mating status. The movement of four T. castaneum genotypes was assessed: (1) field-derived phosphine-susceptible beetles, (2) laboratory-cultured, phosphine-susceptible beetles, (3) laboratory-cultured, phosphine-resistant beetles and (4) resistant introgressed beetles that are almost identical genetically to the laboratory-susceptible population. Odour preference was similar across all four genotypes as the commercially available T. castaneum aggregation pheromone and cotton seeds appeared to be stronger motivators for movement compared to whole wheat flour. Unmated beetles clearly responded more strongly to the aggregation pheromone lure compared to mated beetles, as mated beetles located resources less frequently and took longer to locate resources. However, no significant difference was observed in the flight response of mated and unmated beetles towards the aggregation pheromone lure. Phosphine resistance status of individual beetles affected their resource localisation abilities and their flight activity negatively. Our results demonstrated pleiotropic effects of phosphine-resistant genes on the movement behaviour of T. castaneum, and this has implications for the spread and development of phosphine resistance outside of phosphine application sites.

Populations of rusty grain beetle, Cryptolestes ferrugineus, a cosmopolitan grain insect pest, have recently developed a very high-level of resistance (1300×) to fumigant phosphine in Australia, threatening the country’s international grain market worth of 8 billion per year. Due to the failure of the registered rates of phosphine, industry urgently needed alternative strategies to manage this new resistance. To address this, an integrated resistance management strategy (IRM) was developed with three core components: 1. regular monitoring and characterization of resistance, 2. developing effective phosphine protocols, and 3. exploring alternative fumigants and treatments. Resistance was monitored across Australia in pest samples collected from farms and centrals storages using a modified FAO method as well as quick knockdown tests. Our results indicated that high-level resistance in C. ferrugineus is prevalent in eastern Australia, particularly in Queensland and New South Wales, particularly in the bulk handing sector. Time to population extinction was assessed in field-derived reference resistant strains using higher dosages (c) and exposure times (t) and the effective c x t regimes were validated in the field for the use by the grain industry. A phosphine concentration of 720 ppm (1 mg L-1) over 18 days was found to be effective in controlling all life stages of phosphine-resistant C. ferrugineus at 25°C. In a parallel research, the suitability of sulfuryl fluoride (ProfumeTM), as an alternative fumigant to phosphine was assessed through laboratory and field efficacy trials. Our results showed that phosphine-resistant insects are highly susceptible to sulfuryl fluoride and a CT of 750 g hm-3 (5.2 mg L-1) over 6 days at 25˚C would be sufficient against all phosphine-resistant pests including C. ferrugineus. While sulfuryl fluoride has promising potential as a “phosphine resistance breaker” the team is currently exploring ways of co-treating phosphine and sulfuryl f

Insecticide resistance is an escalating global issue for a wide variety of agriculturally important pests. The genetic basis and biochemical mechanisms of resistance are well characterized in some systems, but little is known about the ecological aspects of insecticide resistance. We therefore designed a laboratory experiment to quantify the progression of phosphine resistance in Tribolium castaneum populations subject to different immigration regimes and selection pressures. Mated resistant females were added to originally susceptible populations under two distinct migration rates, and in addition, half of the populations in each migration treatment were exposed to selection pressures from phosphine fumigation. The progression of phosphine resistance was assessed by screening beetles for the resistance allele at rph2. Phosphine resistance increased slowly in the low migration treatment and in the absence of selection, as expected. But at the higher migration rate, the increase in frequency of the resistance allele was lower than predicted. These outcomes result from the high levels of polyandry known in T. castaneum females in the laboratory, because most of the Generation 1 offspring (86%) were heterozygous for the rph2 allele, probably because resistant immigrant females mated again on arrival. Phosphine resistance was not fixed by fumigation as predicted, perhaps because susceptible gametes and eggs survived fumigation within resistant females. In terms of phosphine resistance progression in populations exposed to selection, the effect of fumigation negated the difference in migration rates. These results demonstrate how species-specific traits relating to the mating system may shape the progression of insecticide resistance within populations, and they have broad implications for the management of phosphine resistance in T. castaneum in the field. ​We specify and discuss how these mating system attributes need to be accounted for when developing guidelines for