Predators and competitors of the mountain pine beetle Dendroctonus ponderosae (Coleoptera: Curculionidae) in stands of changing forest composition associated with elevation

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Verbenone-releasing flakes protect individual Pinus contorta trees from attack by Dendroctonus ponderosae and Dendroctonus valens (Coleoptera: Curculionidae, Scolytinae)

1 In a study site in interior northern California, twenty individual lodgepole pines Pinus contorta were sprayed with a suspension of DISRUPT Micro‐Flake^® Verbenone (4,6,6‐trimethylbicyclo(3.1)hept‐3‐en‐2‐one) Bark Beetle Anti‐Aggregant flakes (Hercon Environmental, Emigsville, Pennsylvania) in water, with sticker and thickener, from ground level to a height of 7 m. Twenty trees sprayed with just water, sticker and thickener served as controls. All trees were baited immediately after spraying with mountain pine beetle Dendroctonus ponderosae aggregation pheromone lures, and lures were refreshed after 4 weeks. 2 Trees treated with verbenone had significantly lower attack density by D. ponderosae than controls at 2, 4, 6 and 8 weeks after application of flakes. 3 None of the treated trees was attacked by red turpentine beetle Dendroctonus valens, whereas control trees averaged nearly two D. valens attacks per tree, 8 weeks after treatment. 4 A dry frass index, used to predict ultimate tree mortality, was significantly higher in control trees than treated trees for all four sampling intervals. This index proved to be a significant predictor of ultimate tree mortality. 5 Ten months after application, treated trees showed significantly lower mortality than control trees.     

Isolation and characterization of 16 microsatellite loci in the mountain pine beetle, Dendroctonus ponderosae Hopkins (Coleoptera: Curculionidae: Scolytinae)

We isolated 16 polymorphic microsatellite loci in the mountain pine beetle (Dendroctonus ponderosae Hopkins) and developed conditions for amplifying these markers in four multiplex reactions. Three to 14 alleles were detected per locus across two sampled populations. Observed and expected heterozygosities ranged from 0.000 to 0.902 and from 0.100 to 0.830, respectively. Three loci deviated from Hardy-Weinberg equilibrium in one sampled population. One of these loci may be sex linked. These markers will be useful in the study of population structure in this important pest species.     

Effect of associated fungi on the immunocompetence of red turpentine beetle larvae,Dendroctonus valens (Coleoptera: Curculionidae: Scolytinae)

Abstract Dendroctonus–fungus symbioses are often considered as the ideal model systems to study the development and maintenance of ectosymbioses, and diverse interactions, including antagonism, commensalism and mutualism, have been documented between these organisms. The red turpentine beetle, Dendroctonus valens LeConte (Coleoptera: Curculionidae: Scolytinae) is a pine‐killing invasive beetle in northern China. Fungi species Ophiostoma minus, Leptographium sinoprocerum, L. terebrantis and L. procerum were associated with this bark beetle. Antagonistic interactions between D. valens and its associated fungi, such as O. minus and L. sinoprocerum, have been demonstrated, but the underlying causes of this phenomenon are unknown. Here, we first found the two tested fungi species retarded the net weight gain of D. valens larvae after completing 3‐day feeding on their media. Furthermore, we provide direct evidence indicating the effect of associated fungi on the immunocompetence of D. valens larvae to explain the documented antagonism. Our results showed that the activity of phenoloxidase and total phenoloxidase in D. valens larvae were significantly upregulated by two strains of associated fungi, O. minus and L. sinoprocerum as compared with the controls. The phenoloxidase ratio increased significantly in the larvae which had fed for 3 days on media inoculated with O. minus. Because insect immune defenses are costly to be deployed, these results could be explored as one of the underlying mechanisms of the documented antagonism.     

Global and comparative proteomic profiling of overwintering and developing mountain pine beetle,Dendroctonus ponderosae (Coleoptera: Curculionidae), larvae

BackgroundMountain pine beetles, Dendroctonus ponderosae Hopkins (Coleoptera: Curculionidae), are native to western North America, but have recently begun to expand their range across the Canadian Rocky Mountains. The requirement for larvae to withstand extremely cold winter temperatures and potentially toxic host secondary metabolites in the midst of their ongoing development makes this a critical period of their lives.ResultsWe have uncovered global protein profiles for overwintering mountain pine beetle larvae. We have also quantitatively compared the proteomes for overwintering larvae sampled during autumn cooling and spring warming using iTRAQ methods. We identified 1507 unique proteins across all samples. In total, 33 proteins exhibited differential expression (FDR < 0.05) when compared between larvae before and after a cold snap in the autumn; and 473 proteins exhibited differential expression in the spring when measured before and after a steady incline in mean daily temperature. Eighteen proteins showed significant changes in both autumn and spring samples.ConclusionsThese first proteomic data for mountain pine beetle larvae show evidence of the involvement of trehalose, 2-deoxyglucose, and antioxidant enzymes in overwintering physiology; confirm and expand upon previous work implicating glycerol in cold tolerance in this insect; and provide new, detailed information on developmental processes in beetles. These results and associated data will be an invaluable resource for future targeted research on cold tolerance mechanisms in the mountain pine beetle and developmental biology in coleopterans.     

Areography of the genus Dendroctonus (Coleoptera: Curculionidae: Scolytinae) in Mexico

Objective To analyse whether the geographical ranges of Dendroctonus species are (1) associated with factors such as host species or elevation, and (2) in agreement with Halffter's Nearctic distribution pattern. (3) To identify and discuss the factors that are likely to act as barriers to the genus’ geographical distribution. (4) To explore whether there is an association between the size of the geographical ranges of Dendroctonus species and the number of Pinus host species used by each of them, and (5) to assess if these host species are most common at the elevations preferred by the individual Dendroctonus species. Site Mexico. Methods Records of 12 species of Dendroctonus were gathered from entomological collections in Mexico. Distribution ranges were defined by using the propinquity method ( Rapoport, 1975a ). Analysed parameters were: (1) geographical distribution of single species, (2) overlapping of species ranges, (3) disjunction patterns and barriers by means of isoprobabilistic lines, based on the morphotectonic subdivision of Mexico ( Ferrusquía‐Villafranca, 1998 ), (4) spatial variation in species richness with respect to latitude and altitude, (5) size of geographical ranges, and (6) host species for each Dendroctonus species. A correlation was determined between area size and number of pine host species. Results The species ranges varied in shape and size. Geographical ranges tend to be discontinuous in shape. Composite patterns showed that disjunctions among ranges do not closely follow Mexico's morphotectonic subdivision. There are repeated discontinuities among individual distributions, which define five areas: (1) Baja California Peninsula, (2) Sierra Madre Occidental (SMOC), (3) northern Sierra Madre Oriental (SMOR), (4) Sierra Madre de Chiapas, and (5) SMOR + Faja Volcanica Transmexicana (FVT) + Sierra Madre del Sur. The isoprobabilistic lines confirm that the inner part of SMOC provides an optimal environment for the genus, and the FVT province constitutes the broader corridor for it in the country. Richness does not directly decrease or increase with latitude. Richness behaviour of the insect is not associated with that of its host. Elevation distributions showed that most Dendroctonus species move within broad margins of tolerance and species richness is concentrated in the montane interval. Dendroctonus attack 24 of the 47 Pinus species distributed in Mexico. Preferred pine species belong predominantly to Leiophyllae, Ponderosae and Oocarpae subsections. The Spearman rank correlation between area size and number of pine host species was not significant. Dendroctonus clearly belongs to a Nearctic distribution pattern (sensu Halffter, 1987 ). Main conclusions Dendroctonus is present in all montane systems of Mexico and its species coexist within a high geographical sympatry. Overlapping of species distribution appears to be the result of two elements – generalized polyphagy inside Pinus and a wide elevation tolerance within mountainous environments. This behaviour, linked to a high vagility, has allowed the genus Dendroctonus to expand its distribution across Mexico and to employ mountainous systems as corridors separated by barriers that exert a low selective filter effect.     

Prepupal diapause and instar IV developmental rates of the spruce beetle, Dendroctonus rufipennis (Coleoptera: Curculionidae, Scolytinae)

The spruce beetle, Dendroctonus rufipennis (Kirby), is an important mortality agent of native spruces throughout North America. The life-cycle duration of this species varies from 1 to 3 years depending temperature. The univoltine cycle (one generation per year) is thought to maximize outbreak risk and accelerate host mortality in established outbreaks. Prepupal diapause is associated with the semivoltine cycle (one generation per 2 years) and we investigated thermal conditions that result in diapause induction. Preliminary experiments used respirometry in an attempt to distinguish the diapause state of experimental insects but the technique was apparently confounded by low respiration before and during pupation, regardless of diapause status. Therefore, diapause induction was deduced using developmental delays. The observed developmental response was not a “switch”, with developmental delay either present or absent, but instead varied continuously. We found that temperatures <15 °C from instar III through mid-instar IV were associated with developmental delays beyond that expected from cool temperatures. Moreover, the duration of exposure to cool temperatures was important in determining the degree of developmental delay. Small, if any, delays were observed if the cumulative exposure to <15 °C was <20 d whereas >40 d cumulative exposure was associated with distinct developmental suppression. Intermediate exposure to cool temperatures resulted in minor developmental delays. We used our results to parameterize a maximum likelihood estimation model of temperature-dependent instar IV developmental rates, including the effect of diapause. This model can be included as part of a spruce beetle phenology model for predicting population dynamics.     

Phylogeography of the bark beetle Dendroctonus mexicanus Hopkins (Coleoptera: Curculionidae: Scolytinae)

Dendroctonus mexicanus is polyphagous within the Pinus genus and has a wide geographical distribution in Mexico and Guatemala. We examined the pattern of genetic variation across the range of this species to explore its demographic history and its phylogeographic pattern. Analysis of the mtDNA sequences of 173 individuals from 25 Mexican populations allowed to us identify 53 geographically structured haplotypes. High haplotype and low nucleotide diversities and Tajima’s D indicate that D. mexicanus experienced rapid population expansion during its dispersal across mountain systems within its current range. The nested clade phylogeographic analysis indicates that the phylogeographic pattern of D. mexicanus is explained by continuous dispersion among lineages from the Sierra Madre Occidental, the Sierra Madre Oriental and the Trans-Mexican Volcanic Belt. However, we also observed isolation events among haplotypes from the Cofre de Perote/Trans-Mexican Volcanic Belt/Sierra Madre Oriental and the Trans-Mexican Volcanic Belt/Sierra Madre del Sur, which is consistent with the present conformation of mountain systems in Mexico and the emergence of geographical barriers during the Pleistocene.     

Ultrastructure of sensilla of the female mountain pine beetle,Dendroctonus ponderosae hopkins (Coleoptera : scolytidae)

The objective of this study is to provide a morphological foundation for electrophysiological studies on the sensilla of D. ponderosae. The sensilla on the antennae, labial and maxillary palps, galeae and fore-tarsi are described. The antennal club has several types of sensilla: (1) multiporous non-socketed pegs of varying lengths innervated by 2 neurons, (2) uniporous socketed pegs innervated by 5 neurons, (3) pegs innervated by only 1 neuron at the base, (4) tapered uniporous cones innervated by 4 neurons, and (5) fluted multiporous, non-socketed cones innervated by 4 neurons. All hairs on the fore-tarsi are innervated by 1 neuron at the base. The labial and maxillary palp-tips have: (1) digitiform organs, (2) campaniform organs, (3) uniporous, socketed pegs innervated by 5 neurons, and (4) non-porous pegs innervated by 3 neurons. Two small, uniporous, socketed pegs innervated by 4 neurons, are set into the maxillary palp-tip sidewall, and a single, sharp-tipped peg, innervated by 1 neuron, is found on the tip. These 2 types are not seen on the labial palps. The ultrastructure of each type of sensillum found on both the maxillary and labial palps is similar; however, the number of uniporous and non-porous pegs on the labial palps is about half those of the maxilla. The maxillary galeae each have 3 types of sensilla: (1) numerous pegs of various sizes innervated by 1 neuron, (2) a single, possibly uniporous socketed peg innervated by 5 neurons, and (3) another single non-porous non-socketed peg innervated by 2 neurons.     

Gut-associated yeast in bark beetles of the genus Dendroctonus Erichson (Coleoptera: Curculionidae: Scolytinae)

Scolytine bark beetles are the most destructive pests of conifers; they sometimes aggregate in such large numbers that they actually kill their hosts. They maintain close relationships with yeasts and fungi, in particular those that are assumed to aid in digestive, detoxification processes and pheromone production. In this study, 403 yeast strains were isolated from the guts, ovaries, eggs and frass of nine bark beetle species in the genus Dendroctonus Erichson. The beetles were collected from 10 conifer species at 34 locations in Mexico, Guatemala and the USA. Yeast identification was based on partial DNA sequences from 18S rDNA, 26S rDNA and internal transcribed spacer (ITS1), as well as morphological and physiological characteristics. A combined phylogenetic analysis delimited 11 clades with sequences similar to Candida arabinofermentans , C. ernobii , C. membranifaciens (including C. lessepsii , Pichia mexicana and P. scolyti ), C. oregonensis , C. piceae , Kuraishia capsulata (including K. capsulata and K. cf. molischiana ), Pichia americana , P. canadensis , P. glucozyma , P. guilliermondii and an undescribed species of Candida . Nucleotide divergences between the major clades were at least 5% while, with the exception of 30 isolates, yeasts within clades differed from named reference species at fewer than 1% of the nucleotide sites. There do not appear to be obligate relationships between particular yeasts and specific anatomical partitions, nor between particular yeasts and bark beetle species. Some yeasts do appear to be preferentially associated with bark beetles feeding on different conifer genera and therefore host plant defences may limit yeast community diversity in Dendroctonus .  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 98 , 325–342.     

Morphological variation associated with dispersal capacity in a tree‐killing bark beetle Dendroctonus ponderosae Hopkins

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Phylogeny of Dendroctonus bark beetles (Coleoptera: Curculionidae: Scolytinae) inferred from morphological and molecular data

Bark beetles in the genus Dendroctonus may attack and kill several species of coniferous trees, some of them causing major economic losses in temperate forests throughout North and Central America. For this reason, they have been widely studied. However, various aspects of the taxonomy and evolutionary history of the group remain contentious. The genus has been subdivided in species groups according to morphological, biological, karyological or molecular attributes, but the evolutionary affinities among species and species groups within the genus remain uncertain. In this study, phylogenetic relationships among Dendroctonus species were reassessed through parsimony‐based cladistic analysis of morphological and DNA sequence data. Phylogenetic inference was based on 36 morphological characters and on mitochondrial DNA sequences of the cytochrome oxidase I (COI) gene. Analyses were carried out for each dataset, as well as for the combined data analysed simultaneously, under equal and implied weights. According to the combined analysis, the genus Dendroctonus is a monophyletic group defined by at least three synapomorphic characters and there are four main lineages of varied composition and diversity within the genus. Within these lineages, several monophyletic groups match, to some extent, species groups defined by previous authors, but certain groups proposed by those authors are polyphyletic or paraphyletic.     

Proteomics Indicators of the Rapidly Shifting Physiology from Whole Mountain Pine Beetle,Dendroctonus ponderosae (Coleoptera: Curculionidae), Adults during Early Host Colonization

We developed proteome profiles for host colonizing mountain pine beetle adults, Dendroctonus ponderosae Hopkins (Coleoptera: Curculionidae). Adult insects were fed in pairs on fresh host lodgepole pine, Pinus contorta Dougl. ex Loud, phloem tissue. The proteomes of fed individuals were monitored using iTRAQ and compared to those of starved beetles, revealing 757 and 739 expressed proteins in females and males, respectively, for which quantitative information was obtained. Overall functional category distributions were similar for males and females, with the majority of proteins falling under carbohydrate metabolism (glycolysis, gluconeogenesis, citric acid cycle), structure (cuticle, muscle, cytoskeleton), and protein and amino acid metabolism. Females had 23 proteins with levels that changed significantly with feeding (p<0.05, FDR<0.20), including chaperones and enzymes required for vitellogenesis. In males, levels of 29 proteins changed significantly with feeding (p<0.05, FDR<0.20), including chaperones as well as motor proteins. Only two proteins, both chaperones, exhibited a significant change in both females and males with feeding. Proteins with differential accumulation patterns in females exhibited higher fold changes with feeding than did those in males. This difference may be due to major and rapid physiological changes occurring in females upon finding a host tree during the physiological shift from dispersal to reproduction. The significant accumulation of chaperone proteins, a cytochrome P450, and a glutathione S-transferase, indicate secondary metabolite-induced stress physiology related to chemical detoxification during early host colonization. The females'' activation of vitellogenin only after encountering a host indicates deliberate partitioning of resources and a balancing of the needs of dispersal and reproduction.     

Electrophysiological and behavioral responses of Dendroctonus frontalis (Coleoptera: Curculionidae) to volatiles isolated from conspecifics

Olfactory sensitivity of the southern pine beetle, Dendroctonus frontalis Zimmermann, to compounds isolated from the mid/hindguts of newly emerged conspecific adults was assayed with coupled gas chromatography-electroantennographic detection. All previously reported pheromones for D. frontalis plus eight additional compounds (fenchyl alcohol, myrtenal, cis-verbenol, trans-pinocarveol, acetophenone, trans-myrtanol, cis-myrtanol, and 2-phenylethanol) consistently elicited antennal responses from at least one sex. The eight additional compounds were assayed individually at three release rates (0.4-0.8, 3-9, and 25-100 mg/d) for the ability to alter D. frontalis responses to traps baited with D. frontalis attractant (4 mg/d frontalin and 17 mg/d alpha-pinene). At the high release rate, cis-verbenol enhanced attraction of D. frontalis females, whereas the other seven compounds significantly reduced attraction of one or both sexes. Acetophenone significantly reduced attraction of male D. frontalis at the low release rate, and five compounds (fenchyl alcohol, trans-pinocarveol, acetophenone, cis-myrtanol, and 2-phenylethanol) reduced attraction of one or both sexes at the intermediate rate. Only acetophenone significantly altered the sex ratio of beetles trapped, decreasing the proportion of males. Attraction of predatory checkered beetles (Cleridae) was enhanced by cis-verbenol released at the high rate but was not altered by any compound inhibitory to D. frontalis. Analyses of volatiles from individual D. frontalis indicated that the majority of the eight compounds were produced in greater quantities by newly emerged beetles than ones attacking pine bolts. Five of the compounds were associated predominantly with one sex. Possible ecological roles of these compounds in the biology of D. frontalis are discussed.     

Polygamy and an absence of fine-scale structure in Dendroctonus ponderosae (Hopk.) (Coleoptera: Curcilionidae) confirmed using molecular markers

An understanding of mating systems and fine-scale spatial genetic structure is required to effectively manage forest pest species such as Dendroctonus ponderosae (mountain pine beetle). Here we used genome-wide single-nucleotide polymorphisms to assess the fine-scale genetic structure and mating system of D. ponderosae collected from a single stand in Alberta, Canada. Fine-scale spatial genetic structure was absent within the stand and the majority of genetic variation was best explained at the individual level. Relatedness estimates support previous reports of pre-emergence mating. Parentage assignment tests indicate that a polygamous mating system better explains the relationships among individuals within a gallery than the previously reported female monogamous/male polygynous system. Furthermore, there is some evidence to suggest that females may exploit the galleries of other females, at least under epidemic conditions. Our results suggest that current management models are likely to be effective across large geographic areas based on the absence of fine-scale genetic structure.     

Fungi associated with Scolytogenes birosimensis (Coleoptera: Curculionidae) infesting Pittosporum tobira

The bark beetle Scolytogenes birosimensis Niijima is suspected to be involved in the decline of Pittosporum tobira (Thunb. ex Murray) Aiton in the coastal areas of Japan. We isolated fungi from adult S. birosimensis in nine different localities in Japan to assess their potential association and predict their contribution to the success of the beetle. Results from morphological identification of associated fungi showed that the beetle was associated with Fusarium solani and Candida spp. Furthermore, molecular analysis showed that F. solani was most closely related to the plant pathogenic fungus F. solani f. sp. mori. Fungal isolation from surface-sterilized, dissected beetles and scanning electron miscroscope (SEM) observation of the body surface suggested that the associated fungi were carried in the pits on the beetles' elytra. These findings contribute to the understanding of the relationships between S. birosimensis and its associated fungi.     

Nutrient-mediated germination of Beauveria bassiana conidia on the integument of the bark beetle Dendroctonus ponderosae (Coleoptera:Scolytidae)

Field-collected adult mountain pine beetles, Dendroctonus ponderosae, were inoculated with the white muscardine fungus, Beauveria bassiana, and thoroughly examined externally with a scanning electron microscope. Germinating conidia were found at a very low incidence, and only on antennal clubs. However, mortality of inoculated controls was high, and B. bassiana was confirmed as the causative agent. Germination on the cuticle was greatly increased by sonication of adult beetles. The hypothesis that hemolymph released through sonication-damaged membranes provided a nutrient stimulus that enhanced conidial germination was tested by placing hemolymph or yeast-malt extract broth on the cuticle of otherwise nontreated beetles, which were then inoculated with conidia. Significant germination occurred on the cuticle of these beetles. Therefore, a limiting factor for conidial germination on the sclerotized cuticle of D. ponderosae is probably a lack of sufficient nutrients.     

Landscape-scale genetic variation in a forest outbreak species, the mountain pine beetle (Dendroctonus ponderosae)

The mountain pine beetle Dendroctonus ponderosae is a native species currently experiencing large-scale outbreaks in western North American pine forests. We sought to describe the pattern of genetic variation across the range of this species, to determine whether there were detectable genetic differences between D. ponderosae occupying different host trees in common localities, and to determine whether there was molecular evidence for a past demographic expansion. Using a combination of amplified fragment length polymorphism (AFLP) and mitochondrial sequencing analyses, we found evidence of genetic structuring among populations that followed a broad isolation-by-distance pattern. Our results suggest that the geographical pattern of gene flow follows the core distribution of the principal D. ponderosae host species, around rather than across the Great Basin and Mojave Deserts. Patterns of haplotype diversity and divergence were consistent with a range-wide population expansion. This signal was particularly pronounced in the northern part of the species' range, where outbreak activity is currently increasing. Using AFLP markers, we were unable to detect significant differences among groups of insects sampled from different host trees in common locations. Incidentally, we found that a large proportion of the polymorphic AFLP markers were gender-specific, occurring only in males. While we did not include these markers in our analyses, this finding warrants further investigation.     

Predicting Dendroctonus pseudotsugae (Coleoptera: Curculionidae) antiaggregation pheromone concentrations using an instantaneous puff dispersion model

An instantaneous puff dispersion model was used to assess concentration fields of the Douglas-fir beetle, Dendroctonus pseudotsugae Hopkins, antiaggregation pheromone, 3-methylcyclohex-2-en-1-one (MCH), within a 1-ha circular plot. Several combinations of MCH release rate and releaser spacing were modeled to theoretically analyze optimal deployment strategies. The combinations of MCH release rate and releaser spacing used in the modeling exercise were based on results of previous field studies of treatment efficacy. Analyses of model results suggest that a release rate up to six times the initial standard, at a correspondingly wider spacing to keep the total amount of pheromone dispersed per unit area constant, may be effective at preventing Douglas-fir beetle infestation. The model outputs also provide a visual representation of pheromone dispersion patterns that can occur after deployment of release devices in the field. These results will help researchers and practitioners design more effective deployment strategies.     

Captures of boll weevils (Coleoptera: Curculionidae) in traps associated with different habitats

Programs to eradicate the boll weevil, Anthonomus grandis grandis Boheman, from cotton, Gossypium hirsutum L., in the United States rely heavily on pheromone traps for monitoring weevil populations in both active and posteradication maintenance programs. Modifications to trapping protocols that increase trap effectiveness should contribute to this eradication effort. Between October 1996 and May 1997 and between September 1997 and April 1998, we compared trap effectiveness, indicated by the numbers of captured weevils, in relation to selected habitat types. Each study period was divided into fall, winter, and spring seasons. Traps were closely associated with seven habitat types, including four types with prominent erect vegetation (brush-lined irrigation canal, brush, sugarcane, and resaca or ox-bow lake) and three types with only low-growing or sparse erect vegetation (irrigation drainage canal, unimproved pasture, and fallow fields). Captures of male and female weevils were statistically similar regardless of season or trapping habitat. Although captures differed significantly among habitats, these differences varied among seasons. Trapping habitats with prominent vegetational features generally produced higher weekly captures of weevils than habitats lacking these features. Also, captures in traps associated with prominent vegetation indicated seasonal differences in weevil activity, with highest captures occurring during the fall. Traps associated with habitats lacking prominent vegetation did not statistically demonstrate seasonal differences. Our results indicate that immediate trap surroundings strongly influence the effectiveness of the boll weevil pheromone trap. These results also suggest that effectiveness of current trapping programs may be improved through purposeful association of traps with selected vegetational features.