Beetle Resistance Research Articles

Effects of sublethal phosphine exposure on respiration rate and dispersal propensity of adult females of Tribolium castaneum

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.

The cytochrome P450 CYP72A552 is key to production of hederagenin-based saponins that mediate plant defense against herbivores.

Plants continuously evolve new defense compounds. One class of such compounds is triterpenoid saponins. A few species in the Barbarea genus produce saponins as the only ones in the large crucifer family. However, the molecular mechanism behind saponin biosynthesis and their role in plant defense remains unclear. We used pathway reconstitution in planta, enzymatic production of saponins invitro, insect feeding assays, and bioinformatics to identify a missing gene involved in saponin biosynthesis and saponin-based herbivore defense. A tandem repeat of eight CYP72A cytochromes P450 colocalise with a quantitative trait locus (QTL) for saponin accumulation and flea beetle resistance in Barbarea vulgaris. We found that CYP72A552 oxidises oleanolic acid at position C-23 to hederagenin. In vitro-produced hederagenin monoglucosides reduced larval feeding by up to 90% and caused 75% larval mortality of the major crucifer pest diamondback moth and the tobacco hornworm. Sequence analysis indicated that CYP72A552 evolved through gene duplication and has been under strong selection pressure. In conclusion, CYP72A552 has evolved to catalyse the formation of hederagenin-based saponins that mediate plant defense against herbivores. Our study highlights the evolution of chemical novelties by gene duplication and selection for enzyme innovations, and the importance of chemical modification in plant defense evolution.

Changes in corn rootworm wing morphology are related to resistance development

The western corn rootworm, Diabrotica virgifera virgifera LeConte, is the most serious pest of maize across the US Corn Belt and now Europe. The beetle has repeatedly demonstrated its ability to adapt to pest management strategies through evolution of resistance to conventional insecticides, the cultural practice of crop rotation and now to the Bacillus thuringiensis (Bt) toxin which is produced by genetically modified maize. In this study, the wing morphology of 358 western corn rootworm adults from Iowa, Indiana and Illinois, USA, was investigated using geometric morphometric procedures. The populations investigated comprised resistant (i.e. soybean–maize rotation and Bt-maize variants) and non-resistant beetle populations. Data analysis was divided into two groups: (1) resistant versus non-resistant and (2) rotation-resistant versus Bt-maize rootworm populations. Results showed that morphological differences exist in the hind-wing shape of both rotation and Bt-maize-resistant versus non-resistant populations and rotation-resistant versus Bt-maize-resistant variants. Across all three types of rootworm variants investigated, the movement of landmarks 8, 9 and 14 drove the wing shape differences found. These landmarks relate to the basal radial vein and are a key anatomical character used to distinguish different wing morphotypes in rootworm. This study demonstrates the utility of hind-wing morphology/shape as an inexpensive and accessible population biomarker for rootworm. With simple equipment (camera mounted microscopes or flatbed scanners) and readily available free software to capture and analyse landmark (shape and size) data, it is possible to effectively monitor pest resistance development and associated field-based population-level differences. The biological implications of the differences in wing shape found and how this relates to rootworm flight and consequently its dispersal and invasion capabilities are also explored.

Are Survivors Different? Genetic-Based Selection of Trees by Mountain Pine Beetle During a Climate Change-Driven Outbreak in a High-Elevation Pine Forest.

Increased mortality of forest trees, driven directly or indirectly by climate change, is occurring around the world. In western North America, whitebark pine, a high elevation keystone species, and lodgepole pine, a widespread ecologically and economically important tree, have experienced extensive mortality in recent climate-driven outbreaks of the mountain pine beetle. However, even in stands experiencing high levels of mortality, some mature trees have survived. We hypothesized that the outbreak acted as a natural selection event, removing trees most susceptible to the beetle and least adapted to warmer drier conditions. If this was the case, genetic change would be expected at loci underlying beetle resistance. Given we did not know the basis for resistance, we used inter-simple sequence repeats to compare the genetic profiles of two sets of trees, survivors (mature, living trees) and general population (trees just under the diameter preferred by the beetles and expected to approximate the genetic structure of each tree species at the site without beetle selection). This method detects high levels of polymorphism and has often been able to detect patterns associated with phenotypic traits. For both whitebark and lodgepole pine, survivors and general population trees mostly segregated independently indicating a genetic basis for survivorship. Exceptions were a few general population trees that segregated with survivors in proportions roughly reflecting the proportion of survivors versus beetle-killed trees. Our results indicate that during outbreaks, beetle choice may result in strong selection for trees with greater resistance to attack. Our findings suggest that survivorship is genetically based and, thus, heritable. Therefore, retaining survivors after outbreaks to act as primary seed sources could act to promote adaptation. Further research will be needed to characterize the actual mechanism(s) of resistance.

Cap 'n' collar C regulates genes responsible for imidacloprid resistance in the Colorado potato beetle, Leptinotarsa decemlineata

The Colorado potato beetle (CPB), Leptinotarsa decemlineata developed resistance to imidacloprid after exposure to this insecticide for multiple generations. Our previous studies showed that xenobiotic transcription factor, cap ‘n’ collar isoform C (CncC) regulates the expression of multiple cytochrome P450 genes, which play essential roles in resistance to plant allelochemicals and insecticides. In this study, we sought to obtain a comprehensive picture of the genes regulated by CncC in imidacloprid-resistant CPB. We performed sequencing of RNA isolated from imidacloprid-resistant CPB treated with dsRNA targeting CncC or gene coding for green fluorescent protein (control). Comparative transcriptome analysis showed that CncC regulated the expression of 1798 genes, out of which 1499 genes were downregulated in CncC knockdown beetles. Interestingly, expression of 79% of imidacloprid induced P450 genes requires CncC. We performed quantitative real-time PCR to verify the reduction in the expression of 20 genes including those coding for detoxification enzymes (P450s, glutathione S-transferases, and esterases) and ABC transporters. The genes coding for ABC transporters are induced in insecticide resistant CPB and require CncC for their expression. Knockdown of genes coding for ABC transporters simultaneously or individually caused an increase in imidacloprid-induced mortality in resistant beetles confirming their contribution to insecticide resistance. These studies identified CncC as a transcription factor involved in regulation of genes responsible for imidacloprid resistance. Small molecule inhibitors of CncC or suppression of CncC by RNAi could provide effective synergists for pest control or management of insecticide resistance.

Phosphine Resistance in North American Field Populations of the Lesser Grain Borer, Rhyzopertha dominica (Coleoptera: Bostrichidae).

Phosphine is the most widely used fumigant for stored grain insect pests, and resistance to phosphine has evolved in several species worldwide. This study was designed to determine the presence of phosphine resistance in 34 populations of Rhyzopertha dominica (F.) collected from the United States and Canada. Adult R. dominica were sampled and subjected to a discriminatory dose toxicity assay of exposure to 20 ppm of phosphine for 20 h of exposure to distinguish a susceptible R. dominica adult by death from a resistant beetle that survives the treatment. All but two of the 34 geographic populations surveyed had some beetles that were resistant to phosphine, and the frequency of resistance varied from 97% in a population from Parlier, California to 0% in beetles from both Carnduff, Saskatchewan and Starbuck, Manitoba. Probit analyses of dose-mortality bioassays with beetles from a laboratory-susceptible strain and those from five of the populations sampled were used to calculate resistance ratio factors (RRs) based on the ratio of LC50 (estimate for the concentration to kill 50% of a test group) in the sampled population to the LC50 for the susceptible strain. The highest RR for the five resistant populations was nearly 596-fold in beetles from Belle Glade, Florida, whereas the lowest RR in that group was 9-fold in Wamego, Kansas. This study revealed that phosphine resistance in R. dominica is common across North America and some populations have levels of resistance that may pose challenges for continued use of phosphine for their management.

Overexpression of a cytochrome P450 and a UDP-glycosyltransferase is associated with imidacloprid resistance in the Colorado potato beetle, Leptinotarsa decemlineata

Current control of insect pests relies on chemical insecticides, however, insecticide resistance development by pests is a growing concern in pest management. The main mechanisms for insecticide resistance typically involve elevated activity of detoxifying enzymes and xenobiotic transporters that break-down and excrete insecticide molecules. In this study, we investigated the molecular mechanisms of imidacloprid resistance in the Colorado potato beetle, Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae), an insect pest notorious for its capacity to develop insecticide resistance rapidly. We compared the transcriptome profiles of imidacloprid-resistant and sensitive beetle strains and identified 102 differentially expressed transcripts encoding detoxifying enzymes and xenobiotic transporters. Of these, 74 were up-regulated and 28 were down-regulated in the resistant strain. We then used RNA interference to knock down the transcript levels of seven up-regulated genes in the resistant beetles. Ingestion of double-stranded RNA successfully knocked down the expression of the genes for three cytochrome P450s (CYP6BQ15, CYP4Q3 and CYP4Q7), one ATP binding cassette (ABC) transporter (ABC-G), one esterase (EST1), and two UDP-glycosyltransferases (UGT1 and UGT2). Further, we demonstrated that silencing of CYP4Q3 and UGT2 significantly increased susceptibility of resistant beetles to imidacloprid, indicating that overexpression of these two genes contributes to imidacloprid resistance in this resistant strain.

Quantifying rates of random mating in western corn rootworm emerging from Cry3Bb1‐expressing and refuge maize in field cages

AbstractThe western corn rootworm (WCR), Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), is the most significant pest of field maize, Zea mays L. (Poaceae), in the USA. Maize plants expressing Bt toxins targeting the corn rootworm complex have been widely adopted and are the primary insecticidal control measure for this pest in North America. Insect resistance management tactics using various refuge structures have been adopted to ensure Bt products will retain durability. An assumption of the refuge strategy is that males and females emerging from Bt and refuge plantings mate randomly; this has not been tested in the field. We conducted cage studies using field populations of WCR in Indiana, USA, to generate empirical field data on mating rates between beetles emerging from Cry3Bb1‐expressing Bt and refuge maize plants. Two refuge configurations were tested; all refuge plants were labeled using the stable isotope 15N. This mark persists in adult beetles after eclosion, allowing for collection and analysis of isotopic ratios of all beetles. Additional data collected included adult emergence rates, timing and sex ratios for each of the treatments, and head capsule size and dry weights of beetles collected. Treatment had a significant effect on dry weight; mean dry weight decreased in Bt‐only treatments. Fisher's exact test of proportions of mating pairs of refuge and Bt insects indicated that mating was not random in 20% strip refuges and 5% seed blend treatments. We found high percentages of beetles that fed on Bt‐expressing plants as larvae, suggesting that mating between resistant beetles may not be rare even if random mating did occur.

Beyond the survival and death of the deltamethrin-threatened pollen beetle Meligethes aeneus: An in-depth proteomic study employing a transcriptome database

Insecticide resistance is an increasingly global problem that hampers pest control. We sought the mechanism responsible for survival following pyrethroid treatment and the factors connected to paralysis/death of the pollen beetle Meligethes aeneus through a proteome-level analysis using nanoLC coupled with Orbitrap Fusion™ Tribrid™ mass spectrometry. A tolerant field population of beetles was treated with deltamethrin, and the ensuing proteome changes were observed in the survivors (resistant), dead (paralyzed) and control-treated beetles. The protein database consisted of the translated transcriptome, and the resulting changes were manually annotated via BLASTP. We identified a number of high-abundance changes in which there were several dominant proteins, e.g., the electron carrier cytochrome b5, ribosomal proteins 60S RPL28, 40S RPS23 and RPS26, eIF4E-transporter, anoxia up-regulated protein, 2 isoforms of vitellogenin and pathogenesis-related protein 5. Deltamethrin detoxification was influenced by different cytochromes P450, which were likely boosted by increased cytochrome b5, but glutathione-S-transferase ε and UDP-glucuronosyltransferases also contributed. Moreover, we observed changes in proteins related to RNA interference, RNA binding and epigenetic modifications. The high changes in ribosomal proteins and associated factors suggest specific control of translation. Overall, we showed modulation of expression processes by epigenetic markers, alternative splicing and translation. Future functional studies will benefit. Biological significanceInsects develop pesticide resistance, which has become one of the key issues in plant protection. This growing resistance increases the demand for pesticide applications and the development of new substances. Knowledge in the field regarding the resistance mechanism and its responses to pesticide treatment provides us the opportunity to propose a solution for this issue. Although the pollen beetle Meligethes aeneus was effectively controlled with pyrethroids for many years, there have been reports of increasing resistance. We show protein changes including production of isoforms in response to deltamethrin at the protein level. These results illustrate the insect's survival state as a resistant beetle and in its paralyzed state (evaluated as dead) relative to resistant individuals.

Dual resistance to lambda-cyhalothrin and dicrotophos in Hippodamia convergens (Coleoptera: Coccinellidae)

Insecticide resistance is usually associated with pests, but may also evolve in natural enemies. In this study, adult beetles of three distinct North American populations of Hippodamia convergens Guérin-Méneville, and the progeny of reciprocal crosses between the resistant and most susceptible population, were treated topically with varying concentrations of lambda-cyhalothrin and dicrotophos. In addition, the LD50s of both insecticides were applied in combination to resistant individuals. The developmental and reproductive performance of each population was assessed in the absence of insecticide exposure to compare baseline fitness. California and Kansas populations were susceptible to both materials, whereas Georgia (GA) beetles exhibited a resistance ratio (RR50) of 158 to lambda-cyhalothrin and 530 to dicrotophos. Inheritance of lambda-cyhalothrin resistance was X-linked, whereas inheritance of dicrotophos resistance was autosomal. Mortality of resistant beetles treated with a mixture of LD50s of both materials was twice that of those treated with lambda-cyhalothrin alone, but not significantly different from those receiving dicrotophos alone. Life history parameters were largely similar among populations, except that Georgia beetles had higher egg fertility relative to susceptible populations. We conclude that the high levels of resistance to lambda-cyhalothrin and dicrotophos in Georgia beetles reflect heavy loads of these insecticides in local environments, most likely the large acreage under intensive cotton cultivation.

Influence of phosphine resistance genes on flight propensity and resource location inTribolium castaneum(Herbst) (Coleoptera: Tenebrionidae): the landscape for selection

Phosphine resistance in Tribolium castaneum Herbst (Coleoptera: Tenebrionidae) has evolved through changes to enzymes involved in basic metabolic pathways. These changes impose metabolic stress and could affect energy-demanding behaviours. We therefore tested whether phosphine resistance alleles impact the movement of these insects in their quest for new resources. We measured walking and flight parameters of four T. castaneum genotypes: (1) a field-derived population, (2) a laboratory cultured, phosphine-susceptible reference strain, (3) a laboratory cultured, phosphine-resistant reference strain, and (4) a resistant introgressed strain that is almost identical genetically to the susceptible population. The temporal pattern of flight was identical across all populations, but resistant beetles took flight significantly less, walked more slowly, and located resources less successfully than did susceptible beetles. Also, the field-derived beetles (proved not to be carrying resistance genes) walked significantly faster and more directly towards food resources, and had a higher propensity for flight when compared to the susceptible laboratory beetles. These negative effects suggest survival of beetles with the resistance alleles will be compromised should they leave phosphine application sites. The field for selection therefore extends beyond the site at which phosphine fumigant imposed its effect, and other mutations are also likely to be affected in this way.

A specialist herbivore pest adaptation to xenobiotics through up-regulation of multiple Cytochrome P450s.

The adaptation of herbivorous insects to their host plants is hypothesized to be intimately associated with their ubiquitous development of resistance to synthetic pesticides. However, not much is known about the mechanisms underlying the relationship between detoxification of plant toxins and synthetic pesticides. To address this knowledge gap, we used specialist pest Colorado potato beetle (CPB) and its host plant, potato, as a model system. Next-generation sequencing (454 pyrosequencing) was performed to reveal the CPB transcriptome. Differential expression patterns of cytochrome P450 complement (CYPome) were analyzed between the susceptible (S) and imidacloprid resistant (R) beetles. We also evaluated the global transcriptome repertoire of CPB CYPome in response to the challenge by potato leaf allelochemicals and imidacloprid. The results showed that more than half (51.2%) of the CBP cytochrome P450 monooxygenases (P450s) that are up-regulated in the R strain are also induced by both host plant toxins and pesticide in a tissue-specific manner. These data suggest that xenobiotic adaptation in this specialist herbivore is through up-regulation of multiple P450s that are potentially involved in detoxifying both pesticide and plant allelochemicals.

Molecular genetic analysis of the spread of resistance to organophosphate insecticides and pyrethroids in populations of the Colorado potato beetle in the Republic of Bashkortostan

Background. We analyzed the spread of mutations in the gene ache - acetylcholinesterase responsible for resistance to the organophosphate insecticides, and in the gene ldvssc1 - electron-sensitive sodium channel, providing kdr-like resistance to pyrethroids in different regions of Republic of Bashkortostan. Materials and methods. Each group included 30-50 overwintered beetles. DNA from beetles was isolated by phenol-chloroform method. Amplification and analysis of genes ache and ldvssc1 were held by bi-PASA (bi-directional PCR amplification of specific allele) according to (Clark et al., 2001). Evaluation of susceptibility to the set of insecticides from classes of POI (aktellik), pyrethroids (decis) was carried out by topical infliction of ethanol solutions of insecticides (1 ml per individual) on the thorax of adults. Diagnostic concentrations of insecticides corresponding with this manner of treatment were determined in the preliminary experiments. Results. In the localities included in the group of southern and eastern regions, frequency distributions coincided. North-western and central group showed excess of phenotypes resistant to organophosphate insecticides compared with a share of genotypes carrying the mutant allele achе, and reducing the incidence of phenotypes resistant to pyrethroids, compared with the frequency of genotypes carrying the mutant allele ldvssc1. Conclusion. The interpretation of these results implies a significant contribution of some unknown component causing the increased level of non-specific resistance to organophosphate insecticides that can be associated with metabolic stability and also with structure and density of the beetle integuments. It should be noted that individuals carrying the mutant allele, providing resistance to pyrethroids, apparently did not have high adaptability, which may be the reason for this discrepancy in the frequencies of occurrence. Polymorphism and mutations in genes controlling metabolism (in particular, a family of genes of cytochrome P 450) should be studied to elucidate the genetic basis of Colorado potato beetle resistance in the territory of the Republic of Bashkortostan.

Heat-induced mortality and expression of heat shock proteins in Colorado potato beetles treated with imidacloprid.

The Colorado potato beetle is an important pest of solanaceous plants in the Northern Hemisphere. Better understanding of its physiological responses to temperature stress and their interactions with still-prevalent chemical control has important implications for the management of this insect. We measured mortality and expression of the Hsp70 heat shock proteins in the Colorado potato beetle larvae exposed to sublethal concentration of the commonly used insecticide imidacloprid, and to supraoptimal temperatures. Both turned out to be significant stress factors, although induction of Hsp70 by imidacloprid observed in the present study was low compared to its induction by the heat. The two factors also interacted with each other. At an extreme temperature of 43 °C, exposure to a sublethal dose of imidacloprid resulted in a significant rise in larval mortality, which was not observed at an optimal temperature of 25 °C. Heat-stressed larvae also failed to respond to imidacloprid by producing more Hsp70. These findings suggest that when field rates of insecticides become insufficient for killing the exposed beetles under optimal temperature conditions due to the evolution of resistance in beetle populations, they may still reduce the probability of resistant beetles surviving the heat shock created by using propane flamers as a rescue treatment.

Diagnostic molecular markers for phosphine resistance in U.S. populations of Tribolium castaneum and Rhyzopertha dominica.

Stored product beetles that are resistant to the fumigant pesticide phosphine (hydrogen phosphide) gas have been reported for more than 40 years in many places worldwide. Traditionally, determination of phosphine resistance in stored product beetles is based on a discriminating dose bioassay that can take up to two weeks to evaluate. We developed a diagnostic cleaved amplified polymorphic sequence method, CAPS, to detect individuals with alleles for strong resistance to phosphine in populations of the red flour beetle, Tribolium castaneum, and the lesser grain borer, Rhyzopertha dominica, according to a single nucleotide mutation in the dihydrolipoamide dehydrogenase (DLD) gene. We initially isolated and sequenced the DLD genes from susceptible and strongly resistant populations of both species. The corresponding amino acid sequences were then deduced. A single amino acid mutation in DLD in populations of T. castaneum and R. dominica with strong resistance was identified as P45S in T. castaneum and P49S in R. dominica, both collected from northern Oklahoma, USA. PCR products containing these mutations were digested by the restriction enzymes MboI and BstNI, which revealed presence or absence, respectively of the resistant (R) allele and allowed inference of genotypes with that allele. Seven populations of T. castaneum from Kansas were subjected to discriminating dose bioassays for the weak and strong resistance phenotypes. Application of CAPS to these seven populations confirmed the R allele was in high frequency in the strongly resistant populations, and was absent or at a lower frequency in populations with weak resistance, which suggests that these populations with a low frequency of the R allele have the potential for selection of the strong resistance phenotype. CAPS markers for strong phosphine resistance will help to detect and confirm resistant beetles and can facilitate resistance management actions against a given pest population.

Discovering candidate genes that regulate resin canal number in Pinus taeda stems by integrating genetic analysis across environments, ages, and populations.

Genetically improving constitutive resin canal development in Pinus stems may enhance the capacity to synthesize terpenes for bark beetle resistance, chemical feedstocks, and biofuels. To discover genes that potentially regulate axial resin canal number (RCN), single nucleotide polymorphisms (SNPs) in 4027 genes were tested for association with RCN in two growth rings and three environments in a complex pedigree of 520 Pinus taeda individuals (CCLONES). The map locations of associated genes were compared with RCN quantitative trait loci (QTLs) in a (P. taeda × Pinus elliottii) × P. elliottii pseudo-backcross of 345 full-sibs (BC1). Resin canal number was heritable (h(2) ˜ 0.12-0.21) and positively genetically correlated with xylem growth (rg ˜ 0.32-0.72) and oleoresin flow (rg ˜ 0.15-0.51). Sixteen well-supported candidate regulators of RCN were discovered in CCLONES, including genes associated across sites and ages, unidirectionally associated with oleoresin flow and xylem growth, and mapped to RCN QTLs in BC1. Breeding is predicted to increase RCN 11% in one generation and could be accelerated with genomic selection at accuracies of 0.45-0.52 across environments. There is significant genetic variation for RCN in loblolly pine, which can be exploited in breeding for elevated terpene content.

Dillapiol: a pyrethrum synergist for control of the Colorado potato beetle.

Dillapiol, the main constituent in dill Anethum sowa Roxb. ex Fleming (Apiaceae) oil and wild pepper, Piper aduncum L. (Piperaceae), is an effective cytochrome P450 inhibitor similar to piperonylbutoxide (PBO). Laboratory and field trials with pyrethrum Chrysanthemum cinerariifolium (Trevir.) vis. extracts combined with dillapiol (1:5 and 1:16 ratio) were effective against both insecticide-susceptible and -resistant Colorado potato beetle Leptinotarsa decemlineata (Say). In the laboratory, pyrethrum efficacy was increased 2.2-fold with the SS strain and 9.1-fold with the RS strains by using pyrethrum + dillapiol. Two field trials with the pyrethrum + dillapiol formulation demonstrated efficacy > or = 10 times than that of pyrethrum alone. The residual activity (half-life) of the combination exposed to direct sunlight was 3 h but it increased to 10.7 h by adding 2% of the sunscreen octylmethoxycinnamate.

Zróżnicowanie poziomów wrażliwości szkodników rzepaku na te same substancje czynne insektycydów na przykładzie słodyszka rzepakowego i chowacza podobnika

Pollen beetle (Meligethes aeneus F.) and cabbage seed weevil (Ceutorhynchus assimilis Payk.) occur very often at the same time in winter and spring oilseed rape in Polish climatic conditions. The aim of the study was to determine the susceptibility of pollen beetle and cabbage shoot weevil to the same, selected active substances of insecticides from the group of pyrethroids, organophosphates and neonicotinoids recommended in Poland. The studies were conducted with the use of contact-stomach method, which involves tested beetles exposition to treated leaves and inflorescences of host plants. The results indicated high or very high pollen beetle resistance to pyrethroid active substances (the exception was tau-fluwaliant to which the pest showed susceptibility or weak resistance) and some level of cabbage seed weevil resistance to neonicotinoids. The results clearly indicate that the protection of oilseed rape in Poland requires continuous monitoring of resistance level of both pests and regular update of control programs for both species. W warunkach klimatycznych Polski, na rzepaku ozimym i jarym, bardzo często występują równocześnie dwa groźne dla tej rośliny szkodniki – słodyszek rzepakowy (Meligethes aeneus F.) i chowacz podobnik (Ceutorhynchus assimilis Payk.). Celem badań było określenie wrażliwości słodyszka rzepakowego i chowacza podobnika na wybrane substancje czynne insektycydów z grupy pyretroidów, związków fosforoorganicznych oraz neonikotynoidów, zalecane w Polsce. Doświadczenia przeprowadzono metodą kontaktowo-żołądkową, polegającą na eksponowaniu badanych chrząszczy na traktowane chemicznie liście i kwiatostany roślin żywicielskich. Wyniki doświadczeń wykazały wysoką lub bardzo wysoką odporność słodyszka rzepakowego na substancje czynne z grupy pyretroidów (wyjątek stanowił tau-fluwalinat, na który szkodnik wykazywał wrażliwość lub słabą odporność) oraz pewien poziom odporności chowacza podobnika na neonikotynoidy. Uzyskane wyniki wyraźnie wskazują, że ochrona rzepaku w Polsce wymaga stałego monitorowania poziomu odporności obu szkodników i na tej podstawie opracowywania strategii ich zwalczania.

EFFICACY OF LONG-LASTING INSECTICIDAL NET (LLIN) IN CONTROLLING TOBACCO BEETLE (LASIODERMA SERRICORNE) IN MALAWI

The tobacco beetle, Lasioderma serricorne, is a serious insect pest of cured tobacco in Malawi. Fumigation with phosphine is the most common method of control for infested tobacco; however, fumigation has no residual effect and repeated fumigation is required in circumstances where reinfestation easily occurs. Refumigation of tobacco is costly and increases the chances of beetle resistance to phosphine. Experiments were conducted in tobacco warehouses in Lilongwe, Malawi to assess the efficacy of long-lasting insecticidal net (LLIN) combined with phosphine fumigation against the tobacco beetle. The adult beetles caught in pheromone traps placed on tobacco stacks covered with LLIN during a 13-week storage period were always significantly fewer than those without LLIN (untreated control). When tobacco stacks were covered with LLIN after fumigation with phosphine, the initial infestation is expected to be zero; the trap catches remained zero for the whole storage period in most cases. These results suggest t...

Modeling a western corn rootworm,Diabrotica virgifera virgifera(Coleoptera: Chrysomelidae), maturation delay and resistance evolution inBtcorn

Emergence delay and female-skewed sex ratios among adults of Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae) from Bt corn have been reported in field studies. The authors used a simulation model to study the effect of a maturation delay and a female-skewed sex ratio for D. v. virgifera emerging from Bt corn on the evolution of Bt resistance. The effect of skewed toxin mortality in one sex on evolution of Bt resistance was insignificant. An emergence delay among resistant beetles from Bt corn slowed resistance evolution. A shift in the time of emergence for homozygous susceptible beetles from Bt corn did not have a significant effect on the evolution of Bt resistance in D. v. virgifera. This simulation study suggested that skewed toxin mortality in one sex and an emergence delay for beetles in Bt corn are not major concerns for managing resistance by D. v. virgifera to single-toxin or pyramided Bt corn.