Density-dependent within-patch movement behavior of two competing species

Movement behavior is central to understanding species distributions, population dynamics and coexistence with other species. Although the relationship between conspecific density and emigration has been well studied, little attention has been paid to how interspecific competitor density affects another species' movement behavior. We conducted releases of two species of competing Tribolium flour beetles at different densities, alone and together in homogeneous microcosms, and tested whether their recaptures-with-distance were well described by a random-diffusion model. We also determined whether mean displacement distances varied with the release density of conspecific and heterospecific beetles. A diffusion model provided a good fit to the redistribution of T. castaneum and T. confusum at all release densities, explaining an average of >60% of the variation in recaptures. For both species, mean displacement (directly proportional to the diffusion rate) exhibited a humped-shaped relationship with conspecific density. Finally, we found that both species of beetle impacted the within-patch movement rates of the other species, but the effect depended on density. For T. castaneum in the highest density treatment, the addition of equal numbers of T. castaneum or T. confusum had the same effect, with mean displacements reduced by approximately one half. The same result occurred for T. confusum released at an intermediate density. In both cases, it was total beetle abundance, not species identity that mattered to mean displacement. We suggest that displacement or diffusion rates that exhibit a nonlinear relationship with density or depend on the presence or abundance of interacting species should be considered when attempting to predict the spatial spread of populations or scaling up to heterogeneous landscapes.

Identification of odorant receptors of Tribolium confusum in response to limonene repellent activity

Tribolium confusum is an important storage pest showing significant resistance to various chemical pesticides, development of botanical pesticides is an effective strategy to resolve above problem and decrease utilization of chemical pesticides. Present study attempts to explore the molecular mechanism about the repellent activity of limonene. When treatment concentration of limonene was 200.00 μg/cm2, the repellent level remained at grade V after 24 hours. Our study showed that limonene could be distinguished by T. confusum antenna with a maximal electroantennography test value of 0.90 mV. Simultaneously, 88 upregulated and 98 downregulated genes were sequenced in limonene-repellent T. confusum, and RT-qPCR analysis showed that four down-regulated and one up-regulated OR genes play an important role in the response to limonene. The repellent rate was decreased by 22.13% mediated with a knockdown of dsTconOR93, while the EAG value of the female and male adults was reduced to 0.26 mV (49.06%) and 0.20 mV (54.05%), respectively. In conclusion, limonene had a strong repellent activity against T. confusum and TconOR93 gene was determined to be a major effector in perception of limonene. This study provides a basis for the development of limonene as a novel botanical pesticide for the control to storage pests, which will reduce the utilization of chemical pesticides and postpone the development of resistance.

Essential Oils: Useful Tools in Storage-Pest Management

This study aimed to verify the level of repellent and mortality effect of two chemical substances (DEET and 2-undecanone) and seven essential oils (EOs), Allium sativum, Artemisia annua, Ocimum basilicum, Lavandula angustifolia, Eucalyptus globulus, Pinus sylvestris, and Curcuma longa. The storage pests Tribolium confusum, Tenebrio molitor, and Acanthoscelides obtectus were exposed to various concentrations in an olfactometer-and-mortality test. The effects were recorded 24-48-72 h after the treatments were applied. A. sativum, E. globulus, and L. augustifolia were found to have significant repellence effects. A substantial lethal effect was observed for A. sativum, E. globulus, and O. basilicum. We also found that even if the most efficient EOs were diluted to low concentrations, they still produced repellent and mortality effects. The presented results indicate that A. sativum and O. basilicum were the most effective against T. confusum and T. molitor; simultaneously, L. angustifolia and C. longa showed high activity against A. obtectus. All of these efficient EOs could be applied as effective bio-control agents in various stored conditions.

Carlina acaulis essential oil nanoemulsion as a new grain protectant against different developmental stages of three stored-product beetles

BACKGROUND

Plant essential oils (EOs) represent eco-friendly alternatives to conventional insecticides for managing pest populations. Carlina acaulis root EO showed a wide insecticidal spectrum, being highly effective against insect pests and vectors, coupled with low mammal toxicity. To boost the chemico-physical properties of this EO and its main active ingredient, carlina oxide, C. acaulis EO was encapsulated in a nanoemulsion [NE, 6% EO (w/w)], and its insecticidal properties evaluated against larvae and adults of Tribolium castaneum, Tribolium confusum and Tenebrio molitor. Two NE concentrations (500 and 1000 ppm) were applied on stored wheat. Mortality was determined after 4, 8 and 16 h and 1, 2, 3, 4, 5, 6 and 7 days.

RESULTS

The NE was toxic to larvae of T. castaneum and T. confusum, killing 93.9% and 98.9% at 1000 ppm after 7 days of exposure, respectively. Tenebrio molitor larvae were tolerant: only 18.9% were dead after 7 days of exposure on stored wheat treated with 1000 ppm NE. However, the NE exhibited high adulticidal activity leading to 85.2% mortality at 1000 ppm, 7 days post-exposure. The mortalities of T. confusum and T. castaneum adults were low (21.4% and 23.3% respectively) at 1000 ppm, 7 days post-exposure.

CONCLUSIONS

A NE based on C. acaulis EO could be regarded as an efficacious green adulticide or larvicide, depending on the target insect species and its life stage, advancing and specifying the pest management strategies of the tested species in an eco-friendly way. © 2022 Society of Chemical Industry.

Cuticular Hydrocarbon Trails Released by Host Larvae Lose their Kairomonal Activity for Parasitoids by Solidification

Successful host search by parasitic wasps is often mediated by host-associated chemical cues. The ectoparasitoid Holepyris sylvanidis is known to follow chemical trails released by host larvae of the confused flour beetle, Tribolium confusum, for short-range host location. Although the hexane-extractable trails consist of stable, long-chain cuticular hydrocarbons (CHCs) with low volatility, the kairomonal activity of a trail is lost two days after release. Here, we studied whether this loss of kairomonal activity is due to changes in the chemical trail composition induced by microbial activity. We chemically analyzed trails consisting of hexane extracts of T. confusum larvae after different time intervals past deposition under sterile and non-sterile conditions. GC-MS analyses revealed that the qualitative and quantitative pattern of the long-chain CHCs of larval trails did not significantly change over time, neither under non-sterile nor sterile conditions. Hence, our results show that the loss of kairomonal activity of host trails is not due to microbially induced changes of the CHC pattern of a trail. Interestingly, the kairomonal activity of trails consisting of host larval CHC extracts was recoverable after two days by applying hexane to them. After hexane evaporation, the parasitoids followed the reactivated host trails as they followed freshly laid ones. Cryo-scanning electron microscopy showed that the trails gradually formed filament-shaped microstructures within two days. This self-assemblage of CHCs was reversible by hexane application. Our study suggests that the long-chain CHCs of a host trail slowly undergo solidification by a self-assembling process, which reduces the accessibility of CHCs to the parasitoid’s receptors as such that the trail is no longer eliciting trail-following behavior.

Beauveria bassiana Endophytic Strain as Plant Growth Promoter: The Case of the Grape Vine Vitis vinifera

The common grape vine, Vitis vinifera, is a widely known plant with commercial and pharmacological value. The plant hosts a variety of microorganisms known as endophytes that can live within the tissues of the plant for a considerable time period, or even their whole life cycle. The fungus Beauveria bassiana is a well-studied endophyte which can colonize a variety of plants in many ways and in different parts of the plant. In this study, we examined the effect of the endophytic fungus B. bassiana on the growth of V. vinifera. The results demonstrated not only a successful colonization of the endophyte, but also a noteworthy impact on the growth of the V. vinifera root without harming the plant in any way. The fungus was also re-isolated from the parts of the plant using inst bait method. Overall, the study demonstrates the capability of B. bassiana to colonize V. vinifera plants, adding to the already existing knowledge of its endophytic activity, and highlighting its beneficial impact on the root growth.

Effects of terpinen-4-ol fumigation on protein levels of detoxification enzymes in Tribolium confusum

Terpinen-4-ol has high fumigating activity to stored-grain pests including Tribolium confusum. To understand the detoxification of terpinen-4-ol in insects, proteomic analysis was performed to identify related proteins and pathways in response to terpinen-4-ol fumigation in T. confusum. By using isobaric tags for relative and absolute quantitation (iTRAQ)-based strategy, 4,618 proteins were obtained from T. confusum adults in the present study. Comparative proteomic analysis showed that 148 proteins were upregulated and 137 proteins were downregulated in beetles under the LC₅₀ of terpinen-4-ol treatment for 24 hr. According to functional classifications, differentially expressed proteins (DEPs) were enriched in xenobiotic metabolism pathways. In the detoxification pathway, the levels of 25 cytochrome P450s, 5 glutathione S-transferases, and 2 uridine diphosphate (UDP)-glucuronosyltransferases were changed, most of which were upregulated in T. confusum exposed to terpinen-4-ol. The results indicated that terpinen-4-ol was potentially metabolized and detoxified by enzymes like P450s in T. confusum.

Species Composition, Temporal Abundance and Distribution of Insect Captures Inside and Outside Commercial Peanut Shelling Facilities

Insect populations were studied within two commercial peanut shelling facilities located in the southeastern United States. Commercially available pheromone/kairomone-baited dome traps and pheromone-baited flight traps were deployed throughout processing and shipping portions of the shelling plants and serviced weekly over one year. Lasioderma serricorne, Tribolium castaneum, Typhaea stercorea, Carpophilus spp., Plodia interpunctella and Cadra cautella were the most common captures across locations. Lasioderma serricorne made up 87% and 88% of all captures in dome traps in plants one and two, respectively. While L. serricorne was not captured during the winter months in flight traps, it was captured with near 100% frequency in dome traps, suggesting that populations persisted throughout the year inside the facilities. Tribolium castaneum populations were active year round. Across insect species and trap type, temperature was a significant covariate for explaining variation in insect counts. After accounting for the effect of temperature, there were always more insects captured in the processing portions of the facilities compared to the shipping areas. A negative linear relationship was observed between captures of L. serricorne and T. castaneum and trap distance from in-shell peanuts entering the shelling facilities. Conversely, fungivores were more evenly distributed throughout all parts of the shelling plants. These data suggest that management efforts should be focused where in-shell peanuts enter to reduce breeding and harborage sites for grain feeding insects.

Comparison of the effects of multiple variables on the levels of infection of the rat tapeworm, Hymenolepis diminuta, in its intermediate host, the confused flour beetle Tribolium confusum

The interaction of the rat tapeworm, Hymenolepis diminuta, with its intermediate beetle host, Tribolium confusum, is a well-studied model system. However, there is so much variation in the methods and designs of the studies that it is difficult to draw comparisons. This study simultaneously compared several aspects of the infection protocol including beetle age, sex, density and mating status; parasite egg condition, infection environment humidity and the times for the three steps of infection: starvation, feeding and post-feeding development. Although statistically limited by low prevalence and intensity levels, we were able to detect the relative effects of the variables. The effects of these variables on prevalence (percent infection) and intensity (mean number of cysticercoids) do not necessarily correlate with each other. Egg condition, reduced starvation times, higher beetle density and longer development times reduced prevalence. However, differences in intensity were only detected with older beetles. When coupled with survivorship data, our study found that our current infection protocol is optimal for infection success. However, the results suggest extending the study to other intermediate hosts and the inclusion of additional variables.

Insecticidal efficacy of six new pyrrole derivatives against four stored-product pests

Several pyrrole derivatives exhibit insecticidal activity and can be effective as grain protectants. In the present study, we evaluate the insecticidal efficacy of six novel pyrrole derivatives, namely methyl 3-(methylthio)-4,6-dioxo-5-phenyl-1,3a,4,5,6,6a-hexahydropyrrolo[3,4-c]pyrrole-1 carboxylate (compound syn) (2a-syn), methyl 3-(methylthio)-4,6-dioxo-5-phenyl-1,3a,4,5,6,6a-hexahydropyrrolo[3,4-c]pyrrole-1-carboxylate (compound anti) (2a-anti), methyl 3-(benzylthio)-4,6-dioxo-5-phenyl-1,3a,4,5,6,6a-hexahydropyrrolo[3,4-c]pyrrole-1-carboxylate (compound syn) (2f-syn), methyl 3-(benzylthio)-4,6-dioxo-5-phenyl-1,3a,4,5,6,6a-hexahydropyrrolo[3,4-c]pyrrole-1-carboxylate (compound anti) (2f-anti), methyl 3-(butylthio)-4,6-dioxo-5-phenyl-2,4,5,6-tetrahydropyrrolo[3,4-c]pyrrole-1-carboxylate (3e), and methyl 2-benzyl-3-(methylthio)-4,6-dioxo-5-phenyl-2,4,5,6-tetrahydropyrrolo[3,4-c]pyrrole-1-carboxylate (0665), against four important species infesting stored products, the rice weevil, Sitophilus oryzae (Coleoptera: Curculionidae), the lesser grain borer, Rhyzopertha dominica (Coleoptera: Bostrychidae), the confused flour beetle, Tribolium confusum (Coleoptera: Tenebrionidae), and the Mediterranean flour moth, Ephestia kuehniella (Lepidoptera: Pyralidae). The six pyrrole derivatives were evaluated on wheat at different doses (0.1, 1, and 10 ppm) and exposure intervals (7, 14, and 21 days). For S. oryzae adults, the highest mortality was recorded at 10 ppm of 2a-syn (36.7%) followed by 2f-syn (32.2%) and 2f-anti (27.8%) after 21 days of exposure. Regarding progeny production, the application of the six pyrrole derivatives significantly reduced offspring emergence if compared with the controls. After 21 days, mortality of R. dominica reached 50% testing 10 ppm of 2f-syn, followed by 2a-syn (46.7%), 2f-anti (41.1%), and 2a-anti (33.3%), while for 3e and 0665, mortality remained low, not exceeding 17.8%. Mortality of T. confusum adults was very low, ranging from 0 to 16.7% after 21 days of exposure. Progeny production was low (< 1.7 individuals per vial) for all doses of the tested pyrrole derivatives, including control vials. For 2a-syn, 2a-anti, 2f-anti, and 0665, no progeny production was recorded testing 1 and 10 ppm, while for 2f-syn and 3e, no offspring emergence was noted testing 10 ppm. For T. confusum larvae, after 21 days of exposure, mortality reached 62.2% testing 10 ppm of 3e followed by 0665 (55.6%) and 2a-anti (42.2%). For E. kuehniella larvae, mortality reached 57.8% at 10 ppm of 2a-syn, followed by the pyrrole derivative 2f-anti (43.3%) after 21 days of exposure. Overall, these results show that the efficacy of pyrrole derivatives strongly varied according to the exposure interval, tested dose, treated insect species and developmental instar. The tested pyrrole derivatives, with special reference to 2a-syn, 2a-anti, 2f-syn, 2f-anti and 0665, are slow-acting compounds exerting relevant toxicity on key stored-product pests over time. They can be considered further for assays with selected blends aiming to develop novel control tools against stored-product pests in real-world conditions.

Case Study: A Practical Application of an Aerosol Treatment in a Commercial Mill

In recent years, there has been an increasing interest and need for alternatives to structural fumigations, and one alternative that has been used across the industry is aerosol insecticides. Previous tests inside a pilot-scale mill demonstrated that aerosol particle size, delivery method, and the spatial configuration of the mill all influenced effectiveness. However, there is no research conducted inside large commercial facilities. The objective of this research was to evaluate a pyrethrin-plus-methoprene aerosol application inside a commercial mill on adult Tribolium confusum Jacquelin duVal, confused flour beetle, directly exposed to the aerosol and residual effects on larvae. Additionally, five aerodynamic particle sizer spectrometers were placed in the facility and recorded instantaneous spray concentration and estimated aerosol deposition. Adult T. confusum exposed nearest to the aerosol application points had the highest percentage of affected adults (>60%). The aerosol also had vertical movement when released at the top of a three-story open room; instantaneous concentrations were recorded on the ground floor. The aerosol residual was highly effective after 6-weeks post aerosol exposure, as 80% of the bioassays did not have any adult emergence from exposed larvae. This research demonstrates a practical use of aerosol insecticides and their potential to be an effective alternative to structural fumigations.

Toxicity of Melaleuca alternifolia essential oil to the mitochondrion and NAD+/NADH dehydrogenase in Tribolium confusum

BACKGROUND

In our previous study, Melaleuca alternifolia essential oil (EO) was considered to have an insecticidal effect by acting on the mitochondrial respiratory chain in insects. However, the mode of action is not fully understood.

METHODS

In this study, we investigated the insecticidal efficacy of the M. alternifolia EO against another major stored-product pest, Tribolium confusum Jacquelin du Val. Rarefaction and vacuolization of the mitochondrial matrix were evident in oil-fumigated T. confusum adults.

RESULTS

Alterations to the mitochondria confirmed the insecticidal effect of the M. alternifolia EO. Furthermore, comparative transcriptome analysis of T. confusum using RNA-seq indicated that most of the differentially expressed genes were involved in insecticide detoxification and mitochondrial function. The biochemical analysis showed that the intracellular NAD+/NADH ratio is involved in the differential effect of the M. alternifolia EO.

DISCUSSION

These results led us to conclude that NAD+/NADH dehydrogenase may be the prime target site for the M. alternifolia EO in insects, leading to blocking of the mitochondrial respiratory chain.

Toxic effects of some insecticides, herbicides, and plant essential oils against Tribolium confusum Jacquelin du val (Insecta: Coleoptera: Tenebrionidae)

Cereals are staple food for many countries and are grown on millions of hectares of land, but much of the harvest is wasted due to losses by pests. To minimize these losses, many pesticides are used which are damaging to the environment and human health. There are debates to get rid of these chemicals but they are still in use at large scale. An alternative control strategy for insect pests in storage houses is the use of botanicals. In this study, four plant essential oils, two plant extracts, two herbicides, and two insecticides were used against Tribolium confusum and the comparison of toxicity was made by calculating LC₅₀ and LT₅₀ values. LC₅₀ values were higher for abamectin (2.09–10.23 mg/L) and cypermethrin (3.41–11.78 mg/L) insecticides followed by neem essential oil (7.39–19.24 mg/L) and citrus extract (10.14–24.50 mg/L). However, LC₅₀ values were maximum in case of jaman plant extract (22.38–176.42 mg/L) followed by two herbicides, Logran (19.66–39.72 mg/L) and Topik (29.09–47.67 mg/L) However, LC₅₀ values were higher for topic herbicide (24.098 ppm) and jaman essential oil (16.383 ppm) after four days of treatment. Abamectin and cypermethrin insecticides, neem essential oil and citrus plant extract also killed adults of T. confusum quicker as compared other essential oils, extracts and herbicides. Results revealed that botanical formulations being environmentally safe could be used instead of highly hazardous pesticides for stored products’ pests. This study also elaborates the non-host toxicity of herbicides commonly applied in our agroecosystem.

A test of the thermal coadaptation hypothesis with ultimate measures of fitness in flour beetles

Whole-organism performance of ectotherms depends on body temperature, which is tightly linked to environmental temperatures. Individuals attempting to optimize fitness must thus select appropriate temperatures. The thermal coadaptation hypothesis posits that T_o for traits closely linked to fitness should match temperatures selected by a species (T_set) and should coevolve with T_set. T_o may mismatch T_set if the thermal reaction norm for fitness is asymmetric. In this study, we examined six traits related to fitness in red and in confused flour beetles (Tribolium castaneum and T. confusum, respectively), including longevity, lifetime reproductive success, reproductive rate, and development time at four temperatures between 23 and 32°C. For reproductive traits, T_o matched T_set whereas for longevity T_o was lower than T_set. Tribolium species have a strongly r-selected life history strategy, therefore reproductive traits are likely more tightly linked to fitness than longevity due to high predation rates at early life stages. We therefore provide support for the thermal coadaptation hypothesis for reproductive traits that are tightly linked to fitness. Our results highlight the importance of knowing the relationships of traits to fitness when studying thermal physiology.

Decoupling of Behavioral Trait Correlation Across Life Stages in Two Holometabolous Insects

Many animal behaviors have a genetic base, and behavioral traits often correlate with one another. In this study, we tested for a behavioral correlation between tonic immobility and walking distance in the larval and adult stages independently of two holometabolous insects. We confirmed a negative correlation of traits between strains in adults of both the species; however, we did not find it in larvae of either species. This suggests that the negative correlation between tonic immobility and walking is decoupled across life stages from larva to adult. In contrast, previous studies have reported that phenotypic correlations between behavioral traits are maintained from larvae to adults in hemimetabolous insects. In addition, our present results differ from previous results with holometabolous insects. Therefore, our results suggest that metamorphosis can change trade-offs between behavioral traits.

Capture of Tribolium castaneum and Tribolium confusum (Coleoptera: Tenebrionidae) in Floor Traps: The Effect of Previous Captures

The impact of prior captures on the trapping performance of floor traps was evaluated for the red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae), and the confused flour beetle, Tribolium confusum Jacquelin du Val (Coleoptera: Tenebrionidae), in laboratory conditions. The effect of trap seeding, adding adults of the same or different species, was evaluated in order to determine possible effects of prior captures in the trap on each species' behavioral responses. The presence of seeded beetles of the same species resulted in an increase in beetle captures for both T. castaneum and T. confusum, but when traps were seeded with the opposite species, there was no increase in beetle captures for either species, and for T. castaneum overall captures in both seeded and unseeded traps was reduced. Overall, T. castaneum tended to have greater captures than T. confusum regardless of the treatment. When the two species were released together, this negated the increased response to seeded traps observed in the single-species treatments. These findings suggest the potential that the presence of beetles in a trap may be influencing the response of beetles in a nearby trap and that T. castaneum and T. confusum when they occur together may influence each other's response to traps.

Susceptibility of Two Strains of the Confused Flour Beetle (Coleoptera: Tenebrionidae) Following Phosphine Structural Mill Fumigation: Effects of Concentration, Temperature, and Flour Deposits

In this study, we evaluated phosphine efficacy against two strains of the confused flour beetle, Tribolium confusum Jacquelin du Val (Coleoptera: Tenebrionidae), one laboratory strain, with no previous exposure to phosphine, and one field strain, originated from the flour mill on which we performed the fumigation. The standard Detia Degesh Phosphine Resistance Kit showed that the adults of the field strain of T. confusum required 4.4 × longer time to be knocked down than the laboratory strain. In order to assess the efficacy of phosphine in the field against these strains, aluminium phosphide (AlP) was applied in a flour mill in Czech Republic, in 2014. In this application, temperature among the six floors of the flour mill varied between 20 and 30°C, relative humidity (RH) between 44 and 78%, and phosphine concentration-time-products (CtP) between 24 and 38 g.m(-3).h(-1). Moreover, the insects were bioassayed in dishes that contained either no commodity or 1, 3, and 5 cm of flour. Nevertheless, despite these variations, all adults and larvae from both strains were dead, regardless of the floor, the quantity of the commodity, and the conditions prevailing. However, larval emergence from eggs that were used in the bioassays for both strains was recorded in some of the locations tested. In addition, larval emergence was negatively correlated with both temperature and RH. At the same time, emergence was generally similar between strains. The results of the present study illustrate that highly visible dead adults and larvae after the application of phosphine falsely imply good fumigation efficacy, given that a considerable number of eggs are very likely to survive in a wider range of conditions, and the concomitant larval emergence may result in rapid population grown right after the fumigation.

Evaluation of Structural Treatment Efficacy against Tribolium castaneum and Tribolium confusum (Coleoptera: Tenebrionidae) Using Meta-Analysis of Multiple Studies Conducted in Food Facilities

The phase out of methyl bromide for the treatment of structures where grain is milled or processed has triggered a need to evaluate the effectiveness of alternative structural treatments such as sulfuryl fluoride and heat. Tribolium castaneum (Herbst) (red flour beetle) and Tribolium confusum Jacquelin du Val (confused flour beetle) (Coleoptera: Tenebrionidae) are primary targets for structural treatments, and impact of treatments on these species was evaluated in this study. Efficacy was measured by comparing beetle captures in pheromone- and kairomone-baited traps immediately before and immediately after treatments. Studies were conducted primarily in commercial wheat mills and rice mills, with the treatments conducted by commercial applicators. A meta-analysis approach was used to evaluate efficacy data collected from 111 treatments applied in 39 facilities. Findings confirm that structural fumigations and heat treatments greatly reduce pest populations within food facilities, but there was significant variation in the efficacy of individual treatments. Generally, the different treatment types (sulfuryl fluoride, methyl bromide, and heat) provided similar reductions in beetle capture using multiple metrics of beetle activity. The novel application of meta-analysis to structural treatment efficacy assessment generated a robust estimate of overall treatment efficacy, provided insights into factors potentially impacting efficacy, and identified data gaps that need further research.

A stringent test of the thermal coadaptation hypothesis in flour beetles

Whole-organism performance depends on body temperature and ectotherms have variable body temperatures. The thermal coadaptation hypothesis posits that thermal reaction norms have coevolved with thermal preference such that organisms attain optimal performance under a narrow range of body temperatures commonly experienced in the wild. Since thermal reaction norms are often similar, researchers interested in the effects of temperature on fitness often use one easily measured thermal reaction norm, such as locomotor performance, and assume it is a good proxy for fitness when testing the thermal coadaptation hypothesis. The extent to which this assumption holds, however, is often untested. In this study, we provide a stringent test of the thermal coadaptation hypothesis in red and in confused flour beetles by comparing the thermal reaction norm for reproductive output to the preferred body temperature range. We also test the assumption that locomotor performance can serve as a proxy for the thermal reaction norm for reproductive output, a more ultimate index of fitness. In both species, we measured the number of eggs laid, righting time, and sprint speed at eight temperatures, as well as the thermal preference in a thermal gradient. The number of eggs laid increased with female sprint speed and with male righting time, and all three performances had similar thermal reaction norms, with 80% of the maximum achieved between 23 and 37°C. Red flour beetles had preferred body temperatures that matched the optimal temperature for performance; confused flour beetles had lower preferred body temperature than the optimal temperature for performance. We found support for the assumption that locomotor performance can serve as a proxy for reproductive output in flour beetles, but we only found evidence for thermal coadaptation in one of the two species.

Long-Term Residual Efficacy of Spinetoram on Concrete and Steel Surfaces for the Management of Three Stored Product Beetle Species

In this study, the residual efficacy of spinetoram on concrete and galvanized steel surfaces was evaluated under fixed laboratory conditions against the rice weevil, Sitophilus oryzae (L.), the confused flour beetle, Tribolium confusum Jacquelin du Val, and the sawtoothed grain beetle, Oryzaephilus surinamensis (L.). Spinetoram was applied at the dose rates of 0.025 and 0.1 mg (active ingredient)/cm(2), on steel surfaces that were stored in continuous darkness and on concrete surfaces that were stored either in continuous darkness or in 12:12 (L:D) photoperiod. The experimental period for the residual effect of spinetoram was 6 mo. Bioassays were conducted for all types of surfaces and storage conditions at monthly intervals starting from the initial application period (seven bioassays in total). For each bioassay, mortality of the exposed adult beetles was measured after 3 and 7 d of exposure. Among the tested species, T. confusum was the least susceptible, regardless of the surface type, storage conditions, and dose rate. Regarding the bioassays conducted in the surfaces stored in darkness, spinetoram proved very persistent and no reduction in the efficacy was noted throughout the experimental period. Moreover, there were no differences in spinetoram efficacy between the two types of surfaces. Conversely, in light [12:12 (L:D)] conditions spinetoram efficacy was notably reduced after the first month, but remained stable for the rest of the period. The results of this study indicate that spinetoram was persistent with long residual efficacy against major stored grain beetle species on the most common types of surfaces in continuous darkness, while the presence of light reduced its efficacy.

Wolbachia Infection Dynamics in Tribolium confusum (Coleoptera: Tenebrionidae) and Their Effects on Host Mating Behavior and Reproduction

Wolbachia interact with their hosts in a broad variety of relationships that range from parasitism to mutualism. To improve the understanding of complex relationships between Wolbachia and host, we performed not only mating and crossing experiments to investigate effects of Wolbachia on mate choice, mating performance, and reproduction in the confused flour beetles Tribolium confusum (Jacquelin du Val), but also quantitative PCR to determine Wolbachia spatiotemporal infection density dynamics within beetles. Wolbachia induced strong cytoplasmic incompatibility, but had no effects on male mate choice and mating performance. Compared with Wolbachia-uninfected females, infected females had very high fecundity irrespective of male's infection status. Wolbachia infection densities in beetles were higher in eggs and adults and in the reproductive tissues and abdomens, whereas Wolbachia density in adults did not differ between sexes and among different ages. These results suggest that Wolbachia have evolved mutualistic interactions with T. confusum, which provides the first evidence of Wolbachia mutualisms in this beetle species. We discussed these findings and their evolutionary implications in light of Wolbachia-host interactions.

The complete mitochondrial genome of the confused flour beetle Tribolium confusum (Coleoptera: Tenebrionidae)

Flour beetles of the genus Tribolium are economically important as destructive cosmopolitan pests of stored flour, corn, peanuts, and other dried agricultural products. The confused flour beetle Tribolium confusum Jacquelin du Val (1868) is one of the most important pest species of flour beetle. Here we sequenced and characterized the complete mitochondrial genome of T. confusum, the entire sequence is 15,813 bp in size with 72.8% AT content. It consists of 13 protein-coding genes (PCGs), 22 transfer RNA (tRNA), 2 ribosomal RNA (rRNA) genes and one major non-coding AT-rich region. The mitogenome of T. confusum exhibits a gene arrangement and content identical to the most common type in insects. All PCGs are start with a typical ATN initiation codon, except for the cox1, which use AAC as its start codon instead of ATN. Ten genes use standard complete termination codon (six TAA, three TAG), whereas the cox2, cox3, nad4 and nad5 genes end with single T. Except for trnS1 ((AGN)), all tRNA genes display typical secondary cloverleaf structures as those of other insects. The sizes of the large and small ribosomal RNA genes are 1277 and 773 bp, respectively. The AT content of the AT-rich region is 79.5%. The 5 bp conserved motif TACTA was found in the intergenic region between trnS2 ((UCN)) and nad1.

Susceptibility of Tribolium confusum (Coleoptera: Tenebrionidae) to Pyrethrin Aerosol: Effects of Aerosol Particle Size, Concentration, and Exposure Conditions

A series of laboratory studies was conducted to assess the effect of droplet size on efficacy of pyrethrin aerosol against adults of Tribolium confusum Jacqueline DuVal, the confused flour beetle. A vertical flow aerosol exposure chamber that generated a standardized particle size diameter was used for these trials. In the first experiments, adults were exposed in the chamber for 2.5-45 min to aerosol dispensed at a volumetric median particle size diameter (VMD) of 16 μm, and then held in the arenas in which they were exposed or transferred to new arenas with or without a flour food source. All adults were initially knocked down when removed from the chamber. Recovery from knockdown decreased as exposure interval increased, but the presence of a food source enhanced recovery at the lower exposure intervals. In the second experiment, the aerosol was applied at a VMD of 2 μm and adults were exposed for between 5 and 75 min. Knockdown of adults was ≤10% when adults were removed from the chamber regardless of exposure time and afterward there was essentially complete recovery of adults. In the third and final experiment, the same 2-μm VMD particle size and exposure times were used, but the concentration of aerosol was increased by ≍4× compared with the previous experiment. In this test, initial knockdown was greater at the higher exposure intervals, but by 3 and 4 d posttreatment, recovery was again essentially 100%. This is the first published test assessing the efficacy of specific aerosol particle sizes on a stored product insect. Results indicate that particle size was a more important factor in conferring toxicity than the actual concentration or number of aerosol particles.