Beetle Emergence Research Articles

Aggregation, Oviposition and Emergence of Hibiscus Seed Beetles (Althaeus hibisci) at a Central Ohio Marsh

Several aspects of the reproductive ecology of the hibiscus seed beetle were investigated during summer 2003 and the succeeding winter and spring. Throughout the flowering period that extended from late Jul. to early Sept., aggregations of adult hibiscus seed beetles (Althaeus hibisci Olivier) were collected from swamp rose mallow (Hibiscus moscheutos L.) flowers at 5 d intervals and counted separately by sex. The occurrence of strongly male-biased sex ratios that decreased progressively during the flowering season, accompanied mid-season by slightly male-biased ratios on incipient fruits, suggests that both the flowers and developing fruits serve as sites frequented by the males to acquire mates. During the apparent peak of beetle activity, a cohort of incipient fruits was examined at 3 d intervals for the presence of beetle eggs. Oviposition began <3 d after corolla abscission and had occurred on nearly 100% of the fruits by day 6. Egg density reached an asymptote at day 12. Adult beetle emergence was monitored from seeds originating from flowers that bloomed during separate dates 5 d apart. The seeds were maintained until spring under weather conditions similar to those at the marsh where they were obtained. From seeds produced by fruits derived from flowers that bloomed early in the season (late Jul.–mid Aug.), beetles emerged in autumn of the same year. However, late-season fruits were colonized by beetles that emerged after mid-winter and thus effectively overwintered in the seed. This corrects previous reports indicating that beetles overwinter exclusively as emerged adults.

How maize root volatiles affect the efficacy of entomopathogenic nematodes in controlling the western corn rootworm?

Because the ferocious maize pest Diabrotica virgifera virgifera LeConte can adapt to all currently used control strategies, focus has turned to the development of novel, more sustainable control methods, such as biological control using entomopathogenic nematodes (EPN). A good understanding of the biology and behaviour of these potential control agents is essential for their successful deployment. Root systems of many maize varieties emit (E)-β-caryophyllene (EβC) in response to feeding by larvae of the beetle D. v. virgifera. This sesquiterpene has been shown to attract certain species of EPN, thereby enhancing their control potential. In this study, we tested the effect of this root-produced volatile on the field efficacy of the three EPN Heterorhabditis bacteriophora, Heterorhabditis megidis and Steinernema feltiae against D. v. virgifera larvae in southern Hungary. By comparing beetle emergence and root damage for two maize varieties, one that emits EβC and one that does not, it was found that root protection by H. megidis and S. feltiae was higher on the emitting variety, but this was not the case for H. bacteriophora. Overall, all three nematode species showed good control potential. We conclude that, if properly applied and in combination with the right maize variety, the release of these nematodes can be as effective as other control methods.

Biological studies of Gasteroclisus rhomboidalis (Coleoptera: curculionidae) on Amaranthus species

In West Africa, the foliage of both wild and cultivated varieties of Amarnathus species is used widely as vegetable and as fodder for cattle. This widely cultivated vegetable is severely attacked by the snouted beetle, Gastreoclisus rhomboidalis. A comprehensive study on some aspects of the biology of G. rhomboidalis has been carried out. The full life cycle of the beetle (from copulation and oviposition through the various immature stages to the emergence of adult beetles) was investigated. It took on the average 40 days for the adult beetle to emerge from the day of oviposition. Studies on the feeding habit of the beetles revealed that the beetles fed heavily on the leaves and can inflict an enormous destruction on the host plant over a short period of time. Generally; the studies have been able to confirm that the larva and adult beetles are the most potent destroyers of the host plant. While the adult beetle fed heavily on the leaves and tender plant stem, the larva when hatched in the plant stem, destroyed the host plant (particularly during the tender ages of between 2 - 3 weeks) with its boring activities causing the plant to wilt and die.

Do Cardinal Directions in Different Acacia Tree Species Affect Biological Activities of Bruchid Beetle, Bruchidius buettikeri Decelle (Bruchidae: Coleoptera), in Riyadh Region, Saudi Arabia

Biological activities of bruchid beetle: Bruchidius buettikeri Decelle (Bruchidae: Coleoptera) were studied in four cardinal directions of Acacia tree species in Huraimila and Salbouk. In Huraimila, two species of Acacia; A. grrrardii, subspecies A. g. negevensis (Iraqi) and A. g. nagednsis (Najdi); and A. ehrenbergiana (Salam) were sampled. In Salbouk, A. tortilis radiana (Samar) was sampled. No significant differences were observed for entrance and exit holes per pod and beetles emergence until 45 days on four cardinal directions of different Acacia tree species, except for entrance holes at Dam and Farm locations on Najdi in Huraimila. However, greater activities were observed in south and east direction in farm locations whereas, in the valley (Abu Gatada, Alyata and Dam locations) more bruchid activities were observed in north and south on Najdi and samar while east and west on Iraqi. Moreover, activities were greater on Acacia trees with greater number of seed per pod. Greater bruchid infestation per pod was found on East direction in the farm locations but in the valley locations no distinct trend was observed. Results showed a significant, positive correlation between bruchid activities and temperature but similar strength negative correlation was observed for rest of various abiotic factors. Moreover, a strong positive correlation was recorded between neonate entrance and number of beetle emergence.

Managing bronze beetle (&lt;i&gt;Eucolaspsis&lt;/i&gt; sp) in Hawkes Bay organic apple orchards using soil cultivation

Bronze beetle (Eucolaspsis sp Coleoptera Chrysomelidae) threatens the economic viability of New Zealands organic pipfruit industry Small plot cultivation trials were conducted during spring to target immature beetles in the soil under apple trees These treatments did not appear to be as effective in the second year as in the previous year although two cultivations significantly reduced beetle emergence at all orchards compared with the control In largescale cultivation trials two cultivations reduced damage to apples by 4661 Sampling immature development stages of the beetles in the soil indicated that cultivation should commence during mid October to target pupae in the top 70 mm of the soil The application of cultivation treatments for controlling bronze beetle on commercial orchards is discussed

Initial Larval Feeding on an Alternate Host Enhances Western Corn Rootworm (Coleoptera: Chrysomelidae) Beetle Emergence onCry3Bb1-Expressing Maize

The potential for rootworm larvae to move between grassy weeds and transgenic maize may be important in resistance management of transgenic rootworm-resistant maize. An experiment was conducted under growth chamber and greenhouse conditions to determine the impact of initial feeding of rootworm larvae on alternate hosts, followed by switching host to transgenic maize, on the development of western corn rootworm (Diabrotica virgifera virgifera LeConte). Two grassy weed species, rootworm-resistant Cry3Bb1 transgenic maize (MON863, YieldGardH Rootworm) and its isoline, were infested with 50 neonate larvae per container four weeks after planting. Large crabgrass (Digitaria sanguinalis (L.) Scop), and giant foxtail, Setaria faberi R. A. W. Herrm both in the Poaceae, were chosen because they were relatively good hosts in previous studies. On the 5 th ,1 0 th , and 15 th d after infestation, the Tullgren funnel technique was used to facilitate larval movement (host-switching) from the original host plants to the final hosts (MON863 or its isoline). Beetle emergence and fecundity were significantly impacted by the original host, the final host, and their interaction. The original and the final host plant also significantly impacted the sex ratio of the beetles. The host-switching date did not impact any of those three variables. Only the original host had a significant impact on egg viability. Significantly more reproductively fit beetles were produced from larvae that fed on an alternate host before moving to transgenic maize than from larvae fed exclusively on transgenic maize. Interactions with alternate hosts may influence transgenic maize resistance

Insecticidal Action of PF2 Lectin from Olneya tesota (Palo Fierro) against Zabrotes subfasciatus Larvae and Midgut Glycoconjugate Binding

Zabrotes subfasciatus (Boheman) is the main pest of common beans (Phaselous vulgaris). Some wild legume seeds may contain lectins with insecticidal activities against this insect. The larval developments of Z. subfasciatus on seeds of Olneya tesota (a desert wild legume) and on artificial seeds containing purified PF2 lectin were evaluated. PF2 susceptibility to proteolysis was assessed by incubation with midgut extract at different times. PF2 binding to midgut glycoconjugates was assessed by histochemistry. A reduced level of oviposition and a lack of emergence of adult beetles were observed in O. tesota seeds (compared to common beans), and in artificial seeds containing PF2 at 0.5 and 1%. PF2 was resistant to larval midgut proteolysis for 24 h, while PHA-E (lectin control) was fully digested after 4 h. Histochemistry analysis of midguts incubated with PF2 showed recognition for microvillae and possibly with peritrophic gel. On the other hand, PHA-E exhibited no interaction with larval midgut glycoproteins. Proteolysis resistance and glycan recognition could in part explain why PF2 is toxic to Z. subfasciatus while PHA is not.

Emergence and Seasonal Activity of the Entomophagous Rove Beetle &lt;I&gt;Aleochara bilineata&lt;/I&gt; (Coleoptera: Staphylinidae) in Canola in Western Canada

Aleochara bilineata Gyllenhal (Coleoptera: Staphylinidae) is an important natural enemy of root maggots (Delia spp.) (Diptera: Anthomyiidae), which are serious pests of brassicaceous crops in North America and Europe. Adults of A. bilineata feed on eggs and larvae of root maggots, and A. bilineata larvae parasitize Delia spp. pupae. Emergence and seasonal activity patterns of A. bilineata were investigated during 2003-2005 in canola (Brassica rapa L. and Brassica napus L.) in central Alberta, Canada, in relation to degree-day (DD) accumulations and Julian date. Captures of A. bilineata adults from pitfall traps within emergence cages situated over canola stubble from the previous year indicated that approximately 428, 493, and 455 DD (soil base 5.57 degrees C) and 187, 189, and 180 Julian days were required for 50% emergence in 2003, 2004, and 2005, respectively (3-yr mean = 185.1 +/- 2.8 Julian days [SEM]). Captures of A. bilineata adults from pitfall traps placed in current canola crops determined that 50% levels of activity density required 379 DD and 180 Julian days in 2004. A logistic model that described the relationship of degree-days and Julian days with emergence of adult beetles was appraised, and good correspondence was evident between predicted and observed cumulative emergence patterns. Emergence and seasonal activity periods of A. bilineata in canola were well synchronized with occurrence of preimaginal life stages of its principal hosts, Delia radicum (L.) and Delia platura Meigen, with beetle emergence beginning shortly after the onset of root maggot oviposition.

The Nutritive Value of Dying Maize and &lt;I&gt;Setaria faberi&lt;/I&gt; Roots for Western Corn Rootworm (Coleoptera: Chrysomelidae) Development

The timing that dying root tissues of Setaria faberi R.A.W. Herrm. and maize, Zea mays L., no longer support growth and development of neonate and second-instar western corn rootworm, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), larvae was evaluated to enhance our understanding of the basic ecology of this pest. Three separate greenhouse experiments were conducted. In the first experiment, glyphosate was used to kill S. faberi. In the second experiment, glyphosate was used to kill maize, and in the final experiment, maize was killed by severing it below the growing point. These experiments evaluated western corn rootworm larvae for survival and growth parameters among living control plants, plants severed or sprayed on the day they were infested, plants severed or sprayed 5 and 10 d before they were infested, and plants planted 5 and 10 d early and severed or sprayed 5 and 10 d before they were infested (the last two treatments were controls for root size). Larvae were sampled from each of these treatments 5, 10, and 15 d after infestation, and beetle emergence was recorded from the remaining pots. When infested on the day of glyphosate spray, significantly fewer larvae were recovered from S. faberi than from living S. faberi. Overall, when infested 5 or 10 d after being sprayed with glyphosate or being severed below the growing point, no significant larval weight gain was recorded from any treatment. Host plant tissue apparently becomes unsuitable for larval growth within the first 5 d after glyphosate spray and severing below the growing point. The implications of these data toward current work involving alternate grassy hosts sprayed with herbicide, the increasing occurrence of volunteer corn, related studies on rootworm-host interactions, and certain adult emergence techniques are discussed along with possible mechanisms as to why the tissue becomes unsuitable so quickly.

Ground-dwelling predators can affect within-field pest insect emergence in winter oilseed rape fields

We investigated, (i) whether the emergence from pupation of two coleopteran pest insect groups in oilseed rape (OSR, Brassica napus L.)—pollen beetles (Meligethes spp. F., Nitidulidae) and stem weevils (Ceutorhynchus pallidactylus Marsh and C. napi Gyll., Curculionidae)—is affected by the exclusion of ground-dwelling predatory arthropods, and (ii) the role for pest control of the widely abundant carabid beetles Anchomenus dorsalis Pontop. and Poecilus cupreus L. Densities of ground-dwelling arthropods were manipulated using enclosures; emerging pest adults were assessed using emergence traps. Where arthropods had been excluded, between two (June sampling) and tenfold (August sampling) more stem weevils emerged than where predators had free access. The addition of 25 adult A. dorsalis m−2 to formerly predator-free enclosures showed similar stem weevil emergence than plots where predators had free access; the addition of 25 adult P. cupreus m−2 did not reduce stem weevil emergence. In August, both A. dorsalis and P. cupreus additions marginally significantly reduced pollen beetle emergence.

Role of Climatic Factors on Damage Incidence by &lt;I&gt;Dermolepida albohirtum&lt;/I&gt; (Coleoptera: Scarabaeidae), in Burdekin Sugarcane Fields, Australia

Inconsistent control of Dermolepida albohirtum (Waterhouse) (Coleoptera: Scarabaeidae) in the period after the removal of organochlorines allowed us to study the impact of climatic variables and insecticide application on subsequent damage in sugarcane (Saccharum spp.). D. albohirtum damage records from the Invicta and Inkerman mill areas of the Burdekin district of North Queensland were compared with climatic averages during spring from 1989 to 2003. D. albohirtum damage demonstrated autocorrelation, indicating that the area of damage will increase from one year to the next if the grub is not effectively controlled. Insecticide use did not significantly impact on the area of damage between 1989 and 2003. Of the climatic variables evaluated, only pan evaporation was significant, and it was inversely related to the subsequent area of grub damage. Therefore, we suggest that weather conditions in spring impact on beetle emergence, feeding, and oviposition. Hot and dry spring weather may reduce beetle activity and ultimately the severity of crop damage, whereas wet and mild spring weather may favor beetle activity and an increase in the area of potential crop damage.

PESTICIDE TREATMENTS AFFECT MOUNTAIN PINE BEETLE ABUNDANCE AND WOODPECKER FORAGING BEHAVIOR

In British Columbia, Canada, management efforts used to control mountain pine beetle (Dendroctonus ponderosae Hopkins) outbreaks have included treatment of infested trees with an organic arsenic pesticide, monosodium methanearsonate (MSMA). Cumulative pesticide applications over a large geographic area have generated concerns about arsenic loading in the environment and potential toxicity to nontarget wildlife. We investigated woodpecker foraging patterns in infested stands with and without MSMA treatment using a combination of tree debarking indices, point count surveys, and radiotelemetry methods in addition to insect flight traps to measure mountain pine beetle emergence. Debarking indices indicated woodpecker foraging of MSMA-treated trees was significantly lower than nontreated trees in all sampling years. However, approximately 40% of MSMA trees had some evidence of foraging. Focal observations of foraging woodpeckers and point count surveys in MSMA treatment areas further confirmed that several species of woodpeckers regularly used MSMA stands during the breeding season. Radio-tagged Hairy (Picoides villosus) and Three-toed (Picoides dorsalis) Woodpeckers spent on average 13% and 23% (range 0-66%) of their time, respectively, in treated stands, despite the fact that these areas only comprised on average 1-2% of their core home range (1 km2). MSMA strongly reduced the emergence of several bark beetle (Coleoptera, Scolytidae) species including the mountain pine beetle, and there was a highly significant positive relationship between Dendroctonus beetle abundance and Three-toed Woodpecker abundance. This study identifies the potential negative impact that forest management practices using pesticides can have on woodpecker populations that depend on bark beetles and their host trees.

Potential strategies to manage bronze beetle (&lt;i&gt;Eucolaspsis&lt;/i&gt; sp) in organic apple orchards

Bronze beetle (Eucolaspsis sp Coleoptera Chrysomelidae) threatens the viability of New Zealands organic pipfruit industry Small plot cultivation trials were conducted during spring to target immature beetles in the soil in a 25 m strip under apple trees A single cultivation treatment in October prevented 56 to 81 of the beetle population from emerging When plots were tilled every second week from October to December 79 to 95 failed to emerge The pattern and timing of bronze beetle emergence during 2006 was consistent between the four trial orchards and with the 2005 season A survey of 20 orchards during November 2006 was unable to link beetle damage levels with management practices and the physical environment New strategies to manage bronze beetle larvae are discussed

PHENIPS—A comprehensive phenology model of Ips typographus (L.) (Col., Scolytinae) as a tool for hazard rating of bark beetle infestation

We developed the model PHENIPS for spatial and temporal simulation of the seasonal development of Ips typographus at the Kalkalpen National Park in Austria. The model is based on a digital elevation model used for interpolation of temperature and solar radiation to calculate the microclimatic conditions (bark temperature) for the beetles’ development. Additionally, the beetles’ phenology at Kalkalpen National Park was monitored along with air and bark temperature measurements. The onset of host tree infestation in spring was estimated using a lower threshold of 16.5 °C for flight activity and a mean thermal sum of 140 degree-days (dd) from beginning of April 1st onward. Rate of brood development was calculated from accumulated degree-days of hourly temperature data using upper and lower temperature thresholds of 38.9 and 8.3 °C, respectively, and a nonlinear function for calculating effective thermal sums. Re-emergence of parental beetles occurred at a time when 49.7% of the thermal sum for total development (557 dd) was reached. The model includes the discontinuance of the beetle's reproductive activity at a day length <14.5 h. The rate of successful hibernation of established broods is predicted by assessing the developmental stage of initiated generations at the beginning of the cold period. For validation we compared the timing of phenological events in the field with predicted events using both, hourly recorded data at trap trees in the terrain and generated daily topoclimatic data. Using topoclimatic data, the onset of infestation was predicted with a mean absolute error of 1.3 days. The observed onset of emergence of filial beetles in the field was estimated with a mean error of 39 dd. Our PHENIPS explicitly considers the strong effects of regional topography and stand conditions on local air and bark temperature and can be used for precise monitoring of the actual state of bark beetle development at the specific stand/tree level. Using topoclimatic data, PHENIPS simulates the maximum number of generations which is necessary to assess the potential impact of bark beetle outbreaks at regional scale. Further applications of PHENIPS for site-specific hazard rating of bark beetle infestation are discussed.

Effects of ultraviolet (254nm) irradiation on egg hatching and adult emergence of the flour beetles, Tribolium castaneum, T. confusum and the almond moth, Cadra cautella.

The eggs of the stored grain pests, Tribolium castaneum (Herbst), T. confusum (Duval) (Coleoptera: Tenebrionidae) and Cadra cautella (Walker) (Lepidoptera; Pyralidae) belonging to three age groups, 1, 2, and 3 days-old, were exposed to ultraviolet (UV) radiation with 254nm wavelength (UV-C) for different durations to determine irradiation effects on egg-hatching and adult emergence. An increase in time of exposure to UV-rays caused a gradual decrease in the percentage of hatching of eggs in all age groups of eggs. No hatching occurred after 24 minutes of exposure in 2 and 3 day-old eggs of T. confusum. C. cautella eggs were less sensitive to UV-rays than were T. castaneum and T. confusum eggs. All the exposure periods significantly reduced the eclosion of adults in all the experimental insects. No adults emerged when 3 day-old eggs of T. castaneum were irradiated for 16 or 24 minutes, or from 2 and 3 day-old eggs T. confusum irradiated for 16 or 24 minutes.

Spatio-temporal distribution and emergence of beetles in arable fields in relation to soil moisture

Predatory beetles contribute to the control of crop pests and are an important food resource for farmland birds. Many of these beetle species overwinter as larvae within agricultural soils, however, their spatio-temporal emergence patterns are poorly understood, even though such knowledge can assist with their management for biocontrol. Soil moisture is considered to be a key factor influencing oviposition site selection and larval survival. The time, density and spatial pattern of Carabidae and Staphylidae emergence was therefore measured across two fields and compared to soil moisture levels in the previous winter and adult distribution in the previous July. The mean density of Carabidae and Staphylidae that emerged between April and harvest within each field was 157 and 86 m-2, indicating that soils are an important over-wintering habitat for beneficial invertebrates and should be managed sympathetically if numbers are to be increased. Of the species that were sufficiently numerous to allow their spatial pattern to be analysed, all showed a heterogeneous emergence pattern, although patches with high emergence were stable over the sampling period. The distribution of eight species was influenced by soil moisture levels in the previous winter and eight species, although not the same, were spatially associated with the distribution of adults in the previous summer suggesting that the females selected oviposition areas with the appropriate soil wetness.

Transmission of the pine wood nematode Bursaphelenchus xylophilus through feeding activity of Monochamus galloprovincialis (Col., Cerambycidae)

Abstract: Transmission of the pinewood nematode (PWN) Bursaphelenchus xylophilus (Steiner &amp; Bührer) Nickle to Pinus pinaster Aiton branches through feeding wounds of its vector in Portugal, Monochamus galloprovincialis Olivier, was studied under laboratory conditions. All the B. xylophilus‐infected beetles transmitted nematodes to branches they fed. The transmission was more frequent during the first 6 weeks after emergence, with transmission peaks during the second and the sixth week. The adult M. galloprovincialis transmitted nematodes for a mean of 5 weeks, independently of the beetle's sex or longevity. No relation was found between beetle feeding intensity and effective transmission of B. xylophilus to the branches. The nematode transmission ceased after the ninth week, even in insects which still had B. xylophilus on their bodies. The longevity of the nematode‐free insects (control group) was slightly higher than the B. xylophilus‐infected beetles, although with no significant difference. The results emphasize the necessity to control the immature stages of M. galloprovincialis prior to emergence and develop efficient strategies to capture and eliminate the recently emerged beetles, as majority of the nematode infection of healthy pine trees occurs during a short period of few weeks after beetle emergence.

Characteristics of the emergence of Monochamus alternatus, the vector of Bursaphelenchus xylophilus (Nematoda: Aphelenchoididae), from Pinus thunbergii logs in Nanjing, China, and of the transmission of the nematodes through feeding wounds

Abstract The pine wood nematode (PWN), Bursaphelenchus xylophilus, which in China and East Asia is vectored by Monochamus alternatus, is the causal agent of pine wilt disease of Japanese black pine, Pinus thunbergii. The vector emergence and the transmission of nematodes through vector feeding on pine twigs were monitored during 2004 and 2005 in Nanjing, China. The emergence started from late April to the end of June and peaked from late May to early June. There were 438 and 927 adults collected in 2004 and 2005, respectively, and approximately 70% of the beetles emerged during the peak period. Visual estimation of the nematode burden on vectors by observation of the atrium of the first abdominal spiracle gave unreliable information. The percentage of beetles carrying PWN of the total number of emerged beetles was between 20 and 30%. Seventy percent of the nematodes were released from beetle cadavers after 3 days of extraction. The sex and longevity of the beetle had no significant relationship with the number of nematodes that remained in cadavers. Transmission of nematodes into pine twigs through beetle feeding started 10 days after emergence of the vector. The period of nematode transmission could last for up to 79 days after beetle emergence. Two types of nematode-transmission curve were found by measuring the number of nematodes transmitted into pine twigs per day. The unimodal pattern peaked between 3 and 6 weeks after adult emergence; the bimodal pattern had two transmission peaks: one between 2 and 3 weeks, and another between 5 to 7 weeks after beetle emergence.

Linking Increasing Drought Stress to Scots Pine Mortality and Bark Beetle Infestations

In the dry Swiss Rhone Valley, Scots pine forests have experienced increased mortality in recent years. It has commonly been assumed that drought events and bark beetles fostered the decline, however, whether bark beetle outbreaks increased in recent years and whether they can be linked to drought stress or increasing temperature has never been studied.In our study, we correlated time series of drought indices from long-term climate stations, 11-year mortality trends from a long-term research plot, and mortality probabilities modeled from tree rings (as an indicator of tree vitality) with documented occurrences of various bark beetle species and a buprestid beetle, using regional Forest Service reports from 1902 to 2003 and advisory cases of the Swiss Forest Protection Service (SFPS) from 1984 to 2005. We compared the historical findings with measured beetle emergence from a 4-year tree felling and breeding chamber experiment.The documented beetle-related pine mortality cases increased dramatically in the 1990s, both in the forest reports and the advisory cases. The incidents of beetle-related pine mortality correlated positively with spring and summer temperature, and with the tree-ring-based mortality index, but not with the drought index. The number of advisory cases, on the other hand, correlated slightly with summer drought index and temperature, but very highly with tree–ring—based mortality index. The tree-ring-based mortality index and observed tree mortality increased in years following drought. This was confirmed by the beetle emergences from felled trees. Following dry summers, more than twice as many trees were colonized by beetles than following wet summers.We conclude that increased temperatures in the Swiss Rhone Valley have likely weakened Scots pines and favored phloeophagous beetle population growth. Beetles contributed to the increased pine mortality following summer drought. Among the factors not addressed in this study, changed forest use may have also contributed to increased beetle populations and Scots pine mortality, whereas air pollution seems to be of lesser importance.

Mountain pine beetle population sampling: inferences from Lindgren pheromone traps and tree emergence cages

Lindgren pheromone traps baited with a mountain pine beetle (Dendroctonus ponderosae Hopkins (Coleoptera: Curculionidae, Scolytinae)) lure were deployed for three consecutive years in lodgepole pine stands in central Idaho. Mountain pine beetle emergence was also monitored each year using cages on infested trees. Distributions of beetles caught in pheromone traps and emergence cages were compared. Each year, mountain pine beetle emergence from infested trees occurred within a 30-d period, although beetles were caught in pheromone traps over a period as long as 130 d. A large proportion of the total number of beetles caught in pheromone traps occurred prior to and following peak emergence from infested trees. Beetles caught in pheromone traps during the main emergence period from infested trees had greater whole-body lipids compared to beetles caught early and late in the flight season. Low lipid content of beetles caught before and after the main emergence period could be the result of a long-distance flight caused by fewer sources of pheromone attraction on the landscape and (or) some proportion of reemerged parents in the sample. Results suggest that pheromone traps disproportionately sample mountain pine beetle populations and that natural pheromone sources may influence the number and timing of beetles caught in synthetically baited traps.