Beetle Populations Research Articles

Spatial distribution and fixed-precision sequential sampling plans for Popillia japonica (Coleoptera: Scarabaeidae) adults in primocane raspberry: influence of foliar insecticides.

The Japanese beetle, Popillia japonica Newman (Coleoptera: Scarabaeidae), an invasive species from northern Japan, was first detected in Minnesota in 1968. According to fruit growers and the Minnesota Department of Agriculture, population size and feeding damage has been an increasing concern since 2010. Based on trap-catch data, populations have recently exceeded 4,000 beetles/trap/week during July-August near raspberry fields, and can increase by an order of magnitude within 7-10 days. The primary goals of this study were to assess the spatial distribution of P. japonica adults in raspberry, and to develop and validate a practical fixed-precision sequential sampling plan for grower use. Taylor's Power Law (TPL) regression was used to characterize the beetle's spatial pattern in research plots and commercial fields, either with or without insecticide applications. We then used Green's plan to develop an enumerative sequential sampling plan to estimate P. japonica density in primocane raspberry. Beetle population data were collected at two locations in southern Minnesota, including the Rosemount Research and Outreach Center, and a commercial field near Forest Lake. The TPL results, via slope comparisons, indicated no significant differences in P. japonica spatial pattern between insecticide treated plots versus untreated plots, or among 4 different insecticides (P>0.05). Utilizing all spatial pattern data, we characterized the distribution of P. japonica beetles to be highly aggregated in raspberry, with TPL slopes ranging from b = 1.38 to 1.55; all slopes were found to be >1.0. Although the slopes were not significantly different, we accounted for variability in spatial pattern by using 33 independent data sets, and the Resampling for Validation of Sampling Plans (RVSP) model to validate a sampling plan with a final average precision level of 0.25 (SEM/mean), recommended for integrated pest management (IPM) purposes. The final sampling plan required an average sample number of only 15, 1-m-row samples, while providing high relative net precision (RNP), and thus a cost-effective, efficient sample plan for growers.

Ant-treehopper mutualism affecting biocontrol of Parthenium hysterophorus by Mexican beetle, Zygogramma bicolorata Pallister

Infestation of a treehopper, Gargara malabarica Ananthasubramanian and Ananthakrishnan (Membracidae, Homoptera) on Parthenium hysterophorus L. and also a myrmicine ant, Lophomyrmex quadrispinosus (Jerdon) (Hymenoptera, Formicidae) tending these treehoppers is reported for the first time. The ant-treehopper association interferes with the biological control of P. hysterophorus by Mexican beetle, Zygogramma bicolorata Pallister (Coleoptera, Chrysomelidae). The Parthenium plants with ants supported significantly lesser number of grubs and adults of Mexican beetle compared to plants without ants. Mean number of Mexican beetle eggs was low on plants with ants, but it was non-significant. Further, the ants were observed to be disturbing the adult Mexican beetles from settling on the Parthenium plants, and this presumably led to the less Mexican beetle population.

Assessing the Impact of Weather Parameters on the Population Dynamics of Insect Pests in Cucurbit Vegetables under Mid-Hill Conditions of Himachal Pradesh

A study focusing on population dynamics of sucking and leaf-eating some insect pests along with their correlation with weather parameters in cucurbits was conducted at research field, Department of Entomology, Dr. YSPUHF, Solan, H.P., India from June-October, 2019 and 2020. The results revealed that Amrasca biguttula biguttula (I), Trialeurodes vaporariorum (W), Aulacophora foveicollis (L), Henosepilachna vigintioctopunctata (F), Liriomyza trifolii (B), Aulacophora sp., were recorded as the major insect pests. In bitter gourd, maximum population of jassids recorded was (2.33/leaf) in first week of August while, maximum whitefly population in bottle gourd (2.96/leaf) during last week of August and in ridge gourd during last week of July (3.76/leaf). The maximum red pumpkin beetle population on bitter gourd (2.4 beetles/plant) and bottle gourd (2.6 beetles/plant) was observed during last week of August while, hadda beetle attained peak population during first and third week of August in ridge gourd (1.0/plant) and bitter gourd (1.1 adults/plant), respectively. Maximum leaf miner infestation (2.7 mines/leaf) in bottle gourd and ridge gourd was observed during first and third week of August. All pest attained maximum population between 30 to 32 SMW when weather parameters values were Tmax: 27.50 to 28.90; Tmin: 20.60 to 20.80 oC; RH: 79 to 80 %; Rainfall: 25.80 to 30.20 mm. Relative humidity and rainfall played major role with non-significant positive influence on the population build-up of these pests in cucurbit crops along with temperature. The present findings on weather-driven pest dynamics can inform strategies to boost crop yields and reduce farmers' economic losses in similar environments.

Plant versus pollinator protection: balancing pest management against floral contamination for insecticide use in Midwestern US cucurbits.

Controlling crop pests while conserving pollinators is challenging, particularly when prophylactically applying broad-spectrum, systemic insecticides such as neonicotinoids. Systemic insecticides are often used in conventional agriculture in commercial settings, but the conditions that optimally balance pest management and pollination are poorly understood. We investigated how insecticide application strategies control pests and expose pollinators to insecticides with an observational study of cucurbit crops in the Midwestern United States. To define the window of protection and potential pollinator exposure resulting from alternative insecticide application strategies, we surveyed 62 farms cultivating cucumber, watermelon, or pumpkin across 2 yr. We evaluated insecticide regimes, abundance of striped and spotted cucumber beetles (Acalymma vittatum [Fabricius] and Diabrotica undecimpunctata Mannerheim), and insecticide residues in leaves, pollen, and nectar. We found that growers used neonicotinoids (thiamethoxam and imidacloprid) at planting in all cucumber and pumpkin and approximately half of watermelon farms. In cucumber, foliar thiamethoxam levels were orders of magnitude higher than the other crops, excluding nearly all beetles from fields. In watermelon and pumpkin, neonicotinoids applied at planting resulted in 4-8wk of protection before beetle populations increased. Floral insecticide concentrations correlated strongly with foliar concentrations across all crops, resulting in high potential exposure to pollinators in cucumber and low-moderate exposure in pumpkin and watermelon. Thus, the highest-input insecticide regimes maintained cucumber beetles far below economic thresholds while also exposing pollinators to the highest pollen and nectar insecticide concentrations. In cucurbits, reducing pesticide inputs will likely better balance crop protection and pollination, reduce costs, and improve yields.

Breeding site segregation and Dutch elm disease fungi carriage percentage of three bark beetle species (Scolytus esuriens, S. chikisanii, and S. japonicus) in a Japanese elm tree in Hokkaido, Japan

ABSTRACT In Japan, three bark beetle species, namely Scolytus esuriens, S. chikisanii, and S. japonicus, have been recently identified as new vectors of Dutch elm disease (DED), although their detailed breeding sites and relation to DED fungi acquisition have not been revealed. We investigated the diameter of branches and a trunk (branch – trunk) at the location of the maternal tunnel (Ømt) and the pupal chamber (Øpc), the distance from the pupal chamber to the bark surface i.e. depth of the pupal chamber (Dpc) on a single Japanese elm tree, and the percentages of bark beetles carrying DED fungi (%bcDED) among those collected from the chamber for three species. The Ømt was 11.0–25.6 cm for S. esuriens, 8.3–23.3 cm for S. chikisanii, and 1.3–3.2 cm for S. japonicus. Therefore, three species were found to exhibit breeding site segregation based on the branch – trunk diameter. The %bcDED were 90.2%, 66.7%, and 40.0% for S. esuriens, S. chikisanii, and S. japonicus, respectively. %bcDED showed an increasing trend with increase in Øpc and Dpc. For DED control, it is necessary to monitor and remove small branches that were previously overlooked to prevent an increase in the population of vector beetles, although %bcDED of bark beetles emerging from small branches tends to be low.

Effectiveness of bioinsecticides for different applications against the main pests of radish

Goal. To determine the technical effectiveness of bioinsecticides against major insect pests of radish (Raphanus sativus (L.) convar. radicula (Pers) Sazon.) grown in open fields, and their impact on plants, yield, and root crop quality. Methods. The study was conducted in accordance with the methods generally accepted in entomology and vegetable growing. During 2020—2022 in open ground conditions on three radish hybrids of different ripeness groups (Adele, Eliza and Stellar) the effectiveness of bioinsecticides Bitoxibacillin-BTU, p. (cell bacteria Bacillus thuringiensis-endospores, titer 1.0 × 10⁹ CFU/ cm3, CS +), 2 l/ha, ACTOVERM FORMULA, CE (abamectin, 18 g/l), 5 l/ha, Lepidocide-BTU, p. (cells of the bacterium Bacillus thuringiensis-var. Kurstaki 9708 L, endospores less than 1 × 109 CFU/cm3), 4 l/ ha, (control). The preparations were applied by spraying plants and fertigation (introduction of fertilizers or pesticides into the irrigation system). Results. On the 14th day after spraying radish plants with Bitoxybacillin-BTU, the population of crucifer flea beetles decreased by 3.9—5.2 times and by 2.8—3.9 times with fertigation. The population of cabbage aphids decreased by 3.9—4.8 and 3.0—3.5 times, and cabbage moth by 5.0—9.0 and 2.7—5.0 times, respectively. The technical effectiveness of Bitoxybacillin-BTU was 76% and 68% against crucifer flea beetles, 78% and 70% against cabbage aphids, and 83% and 73% against cabbage moth. The application of ACTOVERM FORMULA by spraying reduced the population of crucifer flea beetles by 2.6—3.3 times and by 2.5—2.7 times with fertigation. The population of cabbage aphids decreased by 2.9—3.6 and 2.5—2.8 times, and cabbage moth by 2.0—3.0 and 2.0—5.0 times, depending on the radish hybrid. The technical effectiveness of ACTOVERM FORMULA against these pests was 67%, 70%, and 77% with spraying, and 60%, 62%, and 73% with fertigation, respectively. No negative effects from spraying or fertigation with bioinsecticides on radish plants were detected. However, radish plants in the spray treatment had higher height (by 2—3 cm), more leaves per plant (by 1 leaf), and a larger leaf surface area (by 0.2—0.8 thousand m²/ha), depending on the hybrid and product. The root mass increased in treatments with double spraying of ACTOVERM FORMULA and Bitoxybacillin-BTU compared to control and fertigation. The use of bioinsecticides Bitoxybacillin- BTU and ACTOVERM FORMULA (2 treatments) during vegetation ensured yields of 25.6—25.8 t/ha for the Adele hybrid with 93—94% marketable root crops, 24.0—25.1 t/ha for the Eliza hybrid with 94—95% marketable root crops, and 23.2—23.7 t/ha for the Stellar hybrid with 95—96% marketable root crops. The root crops had high dry matter content (Adele: 7.9—8.2%, Eliza: 6.2—6.3%, Stellar: 6.5—6.7%), total sugars (Adele: 2.4—2.5%, Eliza: 2.1—2.2%, Stellar: 2.6%), and ascorbic acid content (Adele: 26.0—26.2 mg/100 g, Eliza: 23.9—24.0 mg/100 g, Stellar: 25.4—25.5 mg/100 g). Conclusions. The application of bioinsecticides Bitoxybacillin-BTU (2 l/ha) and ACTOVERM FORMULA (5 l/ ha) is an effective method for controlling sucking pests in radish crops. Double spraying of radish plants at BBCH 0—9 and BBCH 12—19 with Bitoxybacillin-BTU (2 l/ha) provided control of crucifer flea beetle (76%), cabbage aphid (78%), and cabbage moth (83%). Double spraying with ACTOVERM FORMULA (5 l/ha) at the same stages provided control of crucifer flea beetle (67%), cabbage aphid (70%), and cabbage moth (77%).

Interplay of Abiotic Factors on Various Phytophagous Beetles in Cucumber Under Different Agro-climatic Conditions

Cucumber (Cucumis sativus L.2n = 14) is one of the widely cultivated summer vegetable crops from the gourd family of Cucurbitaceae which is native to India. The climatic conditions of northeast India especially Assam are highly conducive for reproduction of insects, and this region has been considered to be a biodiversity hotspot. Moreover, this region has huge potential for the production of vegetable crops especially cucurbits, but insect pests like fruit flies, pumpkin beetle and sucking pests are major limiting factors for successful cultivation of cucurbits like cucumber etc. Therefore, understanding population fluctuation in the field in relation to losses caused by insect pests are a function of their population dynamics which needs to be thoroughly studied. In view of above factors, an investigation on “Interplay of Abiotic and Biotic Factors on various phytophagous beetles of Cucumber Under Different Agro- Climatic Conditions” was carried out at Horticultural Farm, Assam Agricultural University, Jorhat. Population of phytophagous beetles were recorded on weekly intervals based on number of beetles per plant at seven days interval on 5 randomly selected plants after appearance of the pest. The results showed that during 2019 -2021 summer season, the red pumpkin beetle first appeared on 24th April 2019 and 7th May 2020 with initial population of 4.51 and 2.23 beetles per plant, respectively. However, maximum beetle populations were recorded on 8thMay 2019 and 3rd July 2020 with 6.15 and 6.52 beetles per plant, respectively.

An integrated methods to manage the corn ground beetle (Zabrus tenebrioides Goeze) in wheat field

This study presents a series of experiments on control techniques in the open field trials to monitor and manage the corn ground beetle (Zabrus tenebrioides Goeze) (Coleoptera: Carabidae). The larval stage is particularly harmful, as it feeds on cereal roots and constructs tunnels that damage the wheat crop while residing in the soil. The primary goal of the study was to investigate the effectiveness of various control measures in managing Z. tenebrioides populations and improving wheat yields. Thus, in Qalanchughan village three wheat varieties, the local (Hawler2, Hwler4) and the imported one (Wafia) were tested in the underground (prevention measures) such as organic fertilizers, biofertilizer, chemical fertilizers and chemical pesticides and aboveground (control measure) like biopesticides and conventional pesticides. Regarding the underground prevention measures the lowest population of insect was 0.48 larvae/M2 with the highest biological yield (7132.22 kg/ha) of the cereal found in combined soil and seed treatment (organic humic acid + seed mycorrhizal fungi). The lowest population was found in the local variety Hawler4 which was 0.61 larvae/M2 and the highest population was found in Wafia which was 1.04 larvae/ M2. On the other hand, the aboveground treatments also differ in their effectiveness against Z. tenebrioides thus the lowest population of the larvae in 1/M2 was found in the chemical pesticide, Alphacypermethrin 0.38 larvae/ M2 that was not significantly different from Eucalyptus globulus extract which was 0.60 larvae/ M2. Furthermore, maximum biological yield and treatment efficiency were found in Alphacypermethrin followed by eucalyptus extract which was (5581.11 kg/ha and 108.54). The biopesticides and plant extracts can be used as part of integrated pest management techniques to lower the beetle populations and encourage sustainable farming.

Effect of Weeding Frequency for the Control of Flea Beetle (Podagrica spp) on the Production and Yield of Okra (Abelmoschus esculentus (L.) Moench) in Zaria, Kaduna State

Field trials were carried out at Samaru, Zaria in the 2022 and 2023 cropping seasons to study the effect of weeding frequencies for the management of flea beetles (Podagrica spp.) on the production and yield of okra (Abelmoschus esculentus L. Moench). A randomized complete block design (RCBD) replicated four times was used to evaluate the four weeding frequencies: no weeding, one weeding, two weeding, three weeding, and four weeding. Data were collected on the number of beetle populations, the number of flowers produced, number of damaged fruits, number of leaves damaged and the weight of the fruits. The results of the present findings demonstrated that, in comparison to other weeding frequency, fruit yield were higher in plots that were weeded four times, while the populations of flea beetles (Podagrica spp.), number of flowers and leaves damaged were significantly (P<0.05) higher in one, two and four weeding compared with no and three weeding frequencies. Fruit damaged weight was considerably (P≤0.05) decreased in two and three weeding. Thus, as part of integrated pest management (IPM) techniques to optimize flea beetle control, this study highlighted the significance of two and three weeding frequencies

Influence of Sphagnum harvesting on arthropod fauna and vegetation with a focus on beetles (Coleoptera) and ants (Hymenoptera: Formicidae)

The harvesting of living peat moss (Sphagnum spec.) for various industrial applications has become increasingly prevalent. The harvesting process involves manual or mechanical extraction of Sphagnum fragments with minor to significant alterations of the habitats. This study investigates the impact of Sphagnum harvesting on arthropod fauna and vegetation structure at two donor sites with small-scale Sphagnum harvest in northwestern Germany. In the first year after the harvest, comparative surveys were carried out between harvested and unharvested reference areas. Arthropods living in and on the upper Sphagnum layer were studied by manually extracting quadrat samples. Vegetation surveys focused on the vascular plant composition and Sphagnum layer thickness as key habitat parameters. Results indicate no substantial effects on the total numbers for most arthropod orders. In contrast, the frequency of ant workers and the number of ant nests were considerably lower in harvested areas compared to reference areas. Vegetation analysis revealed that the shortening of the Sphagnum hummocks led to a homogenization of the vegetation structure and alterations in species composition in favor of moisture-loving species. Although no significant effects on total beetle populations were observed, the abundance of bog generalists and specialists was significantly reduced in harvest areas. Certain species displayed preferences for harvested or reference areas. Future harvesting practices should consider preserving vulnerable arthropod species and restricting harvesting to a small scale to mitigate adverse effects on bog ecosystems.

Testing metabolic cold adaptation and the climatic variability hypothesis in two latitudinally distant populations of a supratidal water beetle

Temperature significantly impacts ectotherm physiology, with thermal tolerance and metabolic traits typically varying with latitude across species ranges. The drivers of this variation remain unclear, however, despite obvious consequences for population persistence and conservation in the face of ongoing global change. This study explored local adaptation and phenotypic plasticity of metabolic rates and thermal limits in the supratidal rockpool beetle Ochthebius lejolisii. Using populations from localities at different ends of the species range that experience contrasting thermal variability, we simultaneously tested two of the major paradigms of spatial physiological ecology: metabolic cold adaptation (MCA) and the climatic variability hypothesis (CVH). Reciprocal acclimation was conducted under spring temperature regimes of both localities, incorporating local diurnal variation. Metabolic rates were measured by closed respirometry, and thermal tolerance limits estimated through thermography. In line with MCA, the higher-latitude population (colder climate) showed higher metabolic rates and temperature coefficients (Q10s) at lower temperatures than the lower-latitude population. As predicted by the CVH, the lower-latitude population (more variable climate) showed higher upper thermal tolerance but only the higher-latitude population was able to acclimate upper thermal limits. This result suggests trade-offs between physiological thermal limits and thermal plasticity in this species. A limited acclimation capacity could make populations on Mediterranean coasts especially vulnerable in the face of projected increases in extreme temperatures under ongoing climate change.

Comparison of ethanol-baited trap designs for ambrosia beetles in orchards in the eastern United States.

Ambrosia beetles (Coleoptera: Curculionidae: Scolytinae) are among the most devastating pests of orchards, nurseries, and forests. Improving trap design and ethanol lures for capturing ambrosia beetles is necessary to develop effective monitoring and management strategies. In this 2-year study, we assessed 4 trap designs and 3 commercially formulated ethanol lures to refine trapping methods tailored for orchard environments in the eastern United States. Our investigation included orchards in 2 regions, Georgia (pecan orchards) and New York (apple orchards), targeting major ambrosia beetle (Coleoptera: Curculionidae) pest species such as Xylosandrus crassiusculus (Motschulsky), X. compactus (Eichhoff), X. germanus (Blandford), and Anisandrus maiche (Stark). Among the trap designs evaluated, clear sticky cards were most effective for capturing ambrosia beetles across orchard locations. Notably, in Georgia, sticky cards paired with specific low-release ethanol lures demonstrated enhanced capture of X. crassiusculus and X. compactus, 2 key ambrosia beetle pests found infesting young pecan trees. Similarly, in New York, sticky cards baited with low-release ethanol lures captured the highest rates of X. germanus and A. maiche, thus indicating its suitability for diverse ambrosia beetle populations. Overall, our study provides practical implications for tailoring trapping protocols to optimize ambrosia beetle management strategies in orchard settings.

Seasonal incidence of major sucking pests of Bt cotton and their natural enemies with relation to weather parameters

Study on population dynamics of major sucking pests infesting Bt cotton showed that aphid, jassid, whitefly and thrips initiated from 28th SMW (2nd week of July), 28th SMW (2nd week of July), 29th SMW (3rd week of July) and 27th SMW (1st week of July), respectively. Peak infestation of aphid (21.20 aphid per 3 leaves) observed during 1st week of December (49th SMW). Jassid population observed highest in 40th SMW (14th WAS) with 9.88 jassid per 3 leaves, while the maximum whitefly population was observed during 43rd with 11.84 whitefly per 3 leaves. Population of thrips reached its peak during 34th SMW (8th WAS) with 15.32 thrips per 3 leaves. The peak population of lady bird beetles (4.52 grubs and adults per plant) was recorded during 43rd SMW (17th WAS) and the peak population of spider was recorded during 34th SMW (8th WAS) i.e. 1.36 spider per plant. Among the different abiotic environmental factors, jassid and whitefly had significant positive correlation with maximum temperature. Significant positive correlation was showed by thrips with minimum temperature. Morning relative humidity and evening relative humidity showed non-significant negative correlation with all sucking pest except thrips. Rainfall had non-significant positive correlation with jassid, whitefly and thrips. Bright sunshine had non-significant positive correlation with all sucking pests except thrips.

Semi‐natural habitat, but not aphid amount or continuity, predicts lady beetle abundance across agricultural landscapes

Abstract The amount of semi‐natural habitat surrounding farm fields is a common but inconsistent predictor of natural enemy populations and predation services. Standard land cover metrics may not accurately capture the actual availability of limiting resources for natural enemies and can miss important dynamics across space and time. Theory from animal movement and landscape ecology predicts that regions with more, spatio‐temporally continuous resources (i.e. food and shelter) should have larger predator populations and enhanced biological control. To test these predictions empirically, we designed a study measuring aphids, lady beetles and predation services in agricultural landscapes in Wisconsin, USA. In two study years, we sampled lady beetles and aphids in 336 crop fields (corn, soybean, alfalfa and small grains) and adjacent semi‐natural habitat patches (grasslands and woodlands) across 24 1.5 km buffer landscapes at four to seven time points each, and in 1 year, we assessed predation rates with sentinel egg cards. We used aphid counts to model habitat‐specific aphid phenologies, from which we calculated landscape indices of prey amount and continuity. These indices, along with semi‐natural habitat area, were used to predict lady beetle abundance. While there were strong differences in the abundance and timing of aphids by habitat, semi‐natural habitat amount was still a better predictor of lady beetle counts and sentinel egg predation than either aphid amount or continuity indices in these landscapes. Synthesis and applications. Our findings confirm the robust relationship between lady beetles and semi‐natural habitat in agricultural landscapes, and highlight the complexities of measuring fine‐scale resource heterogeneity in real landscapes. Retaining or adding woodland and grassland patches in agricultural landscapes is likely to support larger lady beetle populations and enhance predation in crop fields. Our results suggest that these habitats may be more important for shelter than prey continuity, though this mechanism warrants further investigation. Future work should continue to refine experimental methods for the successful integration of landscape ecology and animal behaviour to support conservation goals.

Drone-based early detection of bark beetle infested spruce trees differs in endemic and epidemic populations

IntroductionEuropean forests face increasing threats due to climate change-induced stressors, which create the perfect conditions for bark beetle outbreaks. The most important spruce forest pest in Europe is the European Spruce Bark Beetle (Ips typographus L.). Effective management of I. typographus outbreaks necessitates the timely detection of recently attacked spruce trees, which is challenging given the difficulty in spotting symptoms on infested tree crowns. Bark beetle population density is one of many factors that can affect infestation rate and symptoms development. This study compares the appearance of early symptoms in endemic and epidemic bark beetle populations using highresolution Unmanned Aerial Vehicles (UAV) multispectral imagery.MethodsIn spring of 2022, host colonization by bark beetles was induced on groups of spruce trees growing in 10 sites in the Southern Alps, characterized by different population density (5 epidemic and 5 endemic). A multispectral sensor mounted on a drone captured images once every 2 weeks, from May to August 2022. The analyses of a set of vegetational indices allowed the actual infested trees’ reflectance features and symptoms appearance to be observed at each site, comparing them with those of unattacked trees.ResultsResults show that high bark beetles population density triggers a more rapid and intense response regarding the emergence of symptoms. Infested trees were detected at least 1 month before symptoms became evident to the human eye (red phase) in epidemic sites, while this was not possible in endemic sites. Key performing vegetation indices included NDVI (Normalized Difference Vegetation Index), SAVI (Soil Adjust Vegetation Index, with a correction factor of 0.44), and NDRE (Normalized Difference Red Edge index).DiscussionThis early-detection approach could allow automatic diagnosis of bark beetles’ infestations and provide useful guidance for the management of areas suffering pest outbreaks.

On the deduction and quantification of irruptive dynamics in mountain pine beetle population and proxy data

AbstractIn attempting to develop a coherent description of the irruptive dynamics of mountain pine beetle (MPB) in North America, we examined a range of cases where authors described the dependency of intrinsic population growth rates on population attack levels. In some cases, detailed population data were used, but in most cases, investigators relied on operational aerial detection survey data. We found that study conclusions varied significantly depending on the type of data analysed and the spatial and temporal dimensions of the monitoring program. The ability to detect an intrinsic Allee effect (i.e., positive density‐dependent growth for low and rising population densities) depended on the type and the intensity of the sampling effort and the extent of sampling in space and time. Consequently, not all studies were able to quantify the irruption threshold (i.e., the population density at which endemic populations may transition towards the epidemic state). Notably, in every study where an Allee effect was demonstrated, investigators also identified at least one extrinsic environmental factor (e.g., winter weather, summer drought, microclimatic effect) that was regulating its strength. Our results suggest that population surveys conducted from the ground are a necessary complement to aerial survey data if the goal is to make inferences about the irruptive potential for MPB populations and the role of environmental factors in shaping that irruptive potential.

The Relationships between the Population Density of Fir Bark Beetles and Niche Breadth.

Bark beetles are a significant link in the chain of diseases that lead to the accelerated dying of firs (Abies alba Mill.), a key species in the cultivation of stable mixed-tree stands. The aim of this work was to evaluate biotic interactions in populations of bark beetles that colonised natural traps made from firs. The tested hypothesis was that the niche breadth of the species increases with the increasing density of the population. The research was carried out in near-natural forests containing fir, growing in the Suchedniów-Oblęgorek Landscape Park in central Poland. Data were collected from 30 traps trees and 30 windfalls in the years 2010-2023. Cryphalus piceae Ratz. prefers heavily weakened trees, as shown by the fact that it colonised all of the natural traps, which lack any defensive reactions. The sampling method used in the study proved effective, as confirmed by the segregation of the niches of all of the bark beetles. Using nonlinear regression (linearisable model and piecewise linear regression), models were constructed that describe the niche breadths of the bark beetles. The niche parameter is correlated with the density of colonisation. The derived models explain around 77-84% of the variation in the niche breadth of bark beetles on natural traps. The mean relative errors of estimation do not exceed 20%. The niche breadth parameter obtained from the derived regression equations may be used in models that describe-for example-the impact of observed climate change on the population dynamics of bark beetles.

An enhanced lure for eastern populations of the North American spruce beetle, Dendroctonus rufipennis Kirby (Coleoptera: Curculionidae).

Regional variation in pheromone production and response has practical implications for the use of semiochemical lures to monitor and control bark beetle populations. We tested 4 lure formulations including 2 new formulations that reflect the pheromone production profiles of western and eastern populations of spruce beetles, Dendroctonus rufipennis Kirby (Coleoptera: Curculionidae), as well as 2 commercially available formulations (current Rocky Mountain lure and current Atlantic lure), in 2 locations in New Brunswick, Canada. In 2 separate years, the new eastern lure containing seudenol, MCOL, and spruce terpenes captured 4 times (2021) and 11 times (2022) more spruce beetles than the current Atlantic lure that consisted of frontalin, seudenol, and spruce terpenes. In 2021, we also captured more eastern larch beetles, Dendroctonus simplex LeConte (Coleoptera: Curculionidae), with the new eastern lure, whereas in 2022, we captured the most D. simplex with the current Atlantic lure, suggesting that more research is needed on D. simplex pheromone production and response across its range. The bark beetle predator, Thanasimus dubius (Fabr.; Coleoptera: Cleridae), did not respond well to the new eastern blend that lacks frontalin, suggesting that response to frontalin is important in finding prey and might be conserved in predator populations. The reduced trap catch of T. dubius to the enhanced lure is beneficial because it does not inhibit natural population control by removing predators from the community. Our study reveals an improved trap lure for eastern populations of spruce beetles and highlights gaps and research needs in bark beetle pheromone ecology.

Dung beetle populations's morphology show evidence of isolation in southern Brazil islands

AbstractInsects in islands may undergo morphological variations related to the geographic isolation faced by their populations. This isolation on insular biota can vary according to the history and characteristics of the islands, as well as the dispersal ability of each species. We investigated the existence of morphological variations in the populations of the Canthon rutilans cyanescens dung beetle from the southern Brazil islands and the nearby mainland. Dung beetles were sampled from December/2020 to April/2021 from five Islands in the Santa Catarina Archipelago and on the mainland through samplings with baited live traps. With geometric morphometry analyses and individuals from each population we compared the body size using an Analysis of Variance and body shape using a Discriminant Analysis with cross‐validation test, followed by a Canonical Variable Analysis to visualize the populations in morphometric space. We found a significant difference in the body length: the population of Ratones Grande Island has smaller individuals than the populations of the mainland, Dona Francisca Island, and Peri on Santa Catarina Island. We also observed that the body shape of the population of Campeche Island differs from the populations of Arvoredo Island and Dona Francisca Island, with a slightly oval body, a larger dorsal region, and a retracted abdomen. These results are consistent with the hypothesis that the populations found on the islands may have remained there since their formation after the Last Glacial Maximum. The isolation and the absence of connectivity between the populations would explain why some islands have populations with distinct morphology.Abstract in Portuguese is available with online material.

Introduced mammalian predators influence demography and trait variation of a New Zealand stag beetle

Most species co-evolve with their predators and develop strategies to avoid predation. This is not possible when a novel predator invades an environment. Native residents must quickly adapt to their new predator or face local extinction. Intense competition for mating opportunities exerts significant selective pressure that can drive the evolution of exaggerated structures across taxa. However, these elaborate traits can elevate the risk of predation for some organisms. In the present study, we observe the effect that rats have had on a population of endemic New Zealand stag beetles, Geodorcus helmsi. Rats in Rakiura | Stewart Island often prey on stag beetles, taking them to a sheltered area to eat them and discard any uneaten parts of the beetle, namely the head and mandibles. We compared the head size, mandible size and numbers of predated and non-predated male and female beetles in three sites in Rakiura | Stewart Island that differ in their abundance of mammalian predators. We found that the population demography and the size of the beetles differed significantly between sites. Additionally, we determined whether predated beetles were larger than non-predated beetles, across multiple years, regardless of site. We found that overall the predated specimens were larger than the non-predated beetles. The trends found here suggest that exaggeration of the male mandibles increases the predation risk of these iconic beetles, acting as a limit to mandible size.Implications for insect conservationOur results show for the first time the effect that novel predators can have on a population of animals with exaggerated sexually selected traits. The presence of novel predators can cause a shift in both population demography and trait distribution.