Mark J. Dalusky

Association between severity of prescribed burns and subsequent activity of conifer-infesting beetles in stands of longleaf pine

A randomized complete block experiment was performed to measure the effect of prescribed, dormant-season burns of three different levels of severity (measured as fuel consumption and soil surface heating) on subsequent insect infestation and mortality of mature longleaf pine (Pinus palustris Mill.). Multiple-funnel traps baited with a low release rate of turpentine and ethanol were used to monitor activity of certain coniferophagous beetles. Non-aggressive species, including the root beetles Hylastes salebrosus Eichhoff and H. tenuis Eichhoff, the ambrosia beetle Xyleborus pubescens Zimmermann, the reproduction weevil Pachylobius picivorus (Germar), and buprestid borers, were attracted to burned plots in numbers that correlated positively with burn severity. Beetle attraction to burned sites was greatest in the first weeks post-burn and disappeared by the second year. Two potential tree-killing bark beetles, Dendroctonus terebrans (Olivier) and Ips grandicollis (Eichhoff), were trapped in significant numbers but exhibited no attraction to burned plots. Tree mortality correlated significantly with the severity of the burns and amounted to 5% of stems in the hottest burn treatment after 3 years. The majority of the mortality was observed in the second and third years post-burn. Attacks of Ips and Dendroctonus bark beetles were apparent on nearly all dead or dying trees, and evidence suggested that root pathogens may have contributed to tree susceptibility to beetle attack and mortality. Our data indicate that selection of burn regimes that reduce or eliminate consumption of duff (e.g., favoring heading fires over backing fires) could significantly reduce mortality of longleaf pine managed for long rotations.

Pheromones in white pine cone beetle, Conophthorus coniperda (Schwarz) (Coleoptera: Scolytidae)

Female white pine cone beetles,Conophthorus coniperda, attacking second-year cones of eastern white pine,Pinus strobus L., produced a sex-specific pheromone that attracted conspecific males in laboratory bioassays and to field traps. Beetle response was enhanced by host monoterpenes. The female-produced compound was identified in volatiles collected on Porapak Q and in hindgut extracts as (+)-trans-pityol, (2R,5S)-(+)-2-(1-hydroxy-1-methylethyl)-5-methyltetrahydrofuran. Males and females produced and released the (E)-(-)-spiroacetal, (5S,7S)-(-)-7-methyl-1,6-dioxaspiro[4.5]decane, which was not an attractant for either sex, but acted as a repellent for males. Porapak Q-trapped volatiles from both sexes contained (+)-trans-pinocarveol and (-)-myrtenol. In addition, hindgut extracts of females containedtrans-verbenol, while males had pinocarvone and verbenone. Work in Georgia and Canada confirmed that the same isomers of pityol and spiroacetal are present in two distinct and widely separated populations ofC. coniperda.

Field Response of Southern Pine Beetle Parasitoids to Some Natural Attractants

Studies were performed to isolate and identify semiochemicals that mediate location of host-infested trees by parasitoids of the southern pine beetle (SPB), Dendroctonus frontalis. Bark or bolts removed from pines infested with SPB broods attracted significant numbers of the hymenopterous parasitoids Spathius pallidus and Roptrocerus xylophagorum to sticky traps placed in an active SPB infestation. Traps baited with the water distillate of SPB brood-infested bark also attracted both species of parasitoids. In contrast, a synthetic bait composed of 18 compounds identified from the headspace volatiles of attractive bark failed to trap parasitoids. The oxygenated and hydrocarbon components of the bark distillate were partitioned by silica gel liquid chromatography, and the resulting two fractions were tested in the field. Parasitoid attraction was greatest when both fractions were released from traps simultaneously. The hydrocarbon fraction, which failed to attract parasitoids, enhanced the weak attractiveness of the oxygenated fraction. Hence, it appears that no single compound is responsible for mediating SPB parasitoid host-tree location and that both oxygenated and hydrocarbon semiochemicals are involved in this process.

Volatiles Associated with Preferred and Nonpreferred Hosts of the Nantucket Pine Tip Moth, Rhyacionia frustrana

Ovipositing female Nantucket pine tip moth, Rhyacionia frustrana, prefer loblolly pine, Pinus taeda L., to slash pine, Pinus elliottii Engelm. except during the first spring following planting of seedlings. Host discrimination by R. frustrana increases as seedlings develop, suggesting that changes in the chemical composition of seedlings may mediate the moths host preferences. Volatile compounds from slash and loblolly pine seedlings were collected using solid-phase microextraction (SPME) during the first year following planting. Four collection periods coincided with adult emergence and oviposition during each of four annual generations of R. frustrana in the Georgia Coastal Plain. Infestation of slash pine peaked during the second tip moth generation and was similar to the loblolly pine infestation level. By the fourth tip moth generation, slash pine infestation levels had declined and diverged considerably from those of loblolly pine. Significant differences in relative quantities of β-pinene, α-phellandrene, limonene, β-phellandrene, bornyl acetate, β-caryophyllene, and an unidentified sesquiterpene occurred between slash and loblolly pine during the fourth generation. However, no strong correlation was observed between any individual compound and host damage that could readily explain the temporal changes in R. frustrana host preference. Gas chromatographic–electroantennographic detection (GC–EAD) analyses of standards identified 19 different seedling- associated compounds that elicited antennal responses from R. frustrana females, indicating that a blend of terpenoids may mediate host discrimination.

Field evaluations of potential aggregation inhibitors for the southern pine beetle, Dendroctonus frontalis (Coleoptera: Curculionidae)

Semiochemicals that inhibit the response of the southern pine beetle, Dendroctonus frontalis Zimmermann, to its aggregation pheromone have been used with varying degrees of success to protect indiv...

Pheromone Production, Attraction, and Interspecific Inhibition among Four Species of Ips Bark Beetles in the Southeastern USA

Hindgut volatiles from attacking, unmated males of Ips avulsus, I. calligraphus, I. grandicollis, and I. pini were analyzed by combined gas chromatography and mass spectrometry. Based on the quantitative identifications of hindguts and subsequent individual aerations, baits were formulated and a combined species-specific subtractive field bioassay was set up for the four bark beetle species. The bioassays were subtractive for the compounds identified in the hindgut analysis of each species, and volatiles identified in sympatric species were added as potential inhibitors alone and in combination. The trap catches from this bioassay revealed strong interspecific inhibition. The subtractive assays showed that I. grandicollis and I. calligraphus share (–)-(4S)-cis-verbenol as one pheromone component, while their second, synergistic pheromone component, (–)-(S)-ipsenol in I. grandicollis and (±)-ipsdienol in I. calligraphus, acts as an interspecific inhibitor to the other species. I. avulsus and I. pini were found to have very similar production of hindgut volatiles, and both use ipsdienol and lanierone as synergistic pheromone components. No beetle-produced interspecific inhibitor was identified between these two species. Lanierone was found to be an interspecific inhibitor for both I. calligraphus and I. grandicollis.

Phenology of the Hemlock Woolly Adelgid (Hemiptera: Adelgidae) in Northern Georgia

Understanding the seasonal phenology of an insect pest in a specific geographic region is essential for optimizing the timing of management actions or research activities. We examined the phenology of hemlock woolly adelgid, Adelges tsugae Annand, near the southern limit of the range of eastern hemlock, Tsuga canadensis (L.) Carriere, in the Appalachians of northern Georgia, where adelgid phenology has not been previously reported. Adelges tsugae- infested hemlock trees were visited at various sites from 2004 - 2007. Two hemlock twigs were collected from each of 3 hemlock trees per site, except during the final 3 months of sampling when 1 twig was collected from each of 3 trees per site. Progrediens adults initiated oviposition by midMay, 2 - 4 weeks earlier than has been reported for more northern parts of the adelgid range. Sistens eggs were present until late-June (2006) or early-July (2004 - 2005). After aestivation, sistens nymphs resumed development by early October. Sistens adults were first found in early January and were present until midMay. Progrediens eggs were noted as early as February (2005 - 2007), were abundant in March and April, and persisted until midMay. Progrediens crawlers were present by early March and occurred throughout the next 2 - 3 months. Progrediens adults were found between midMay and late June. This information may be used to help optimize release of biological control agents to insure proper synchronization with adelgid life stages and to aid in collection of food for predator rearing facilities.

Effects of a Broad Spectrum and Biorational Insecticides on Parasitoids of the Nantucket Pine Tip Moth (Lepidoptera: Tortricidae)

Abstract We examined effects of aerial application of acephate (Orthene), Bacillus thuringiensis variety kurstaki Berliner (Foray), and tebufenozide (Mimic) on larval/pupal parasitoids of the Nantucket pine tip moth, Rhyacionia frustrana (Comstock), in the southwestern Georgia coastal plain. Parasitism of tip moths in acephate-treated plots was significantly lower than in untreated plots. Bacillus thuringiensis and tebufenozide showed no significant effects on parasitism. A tachinid, Lixophaga mediocris Aldrich, comprised a significantly greater proportion of emerging parasitoids in acephate-treated than in untreated control plots, whereas a chalcidid, Haltichella rhyacioniae Gahan, was less abundant in the acephate-treated plots. Acephate has a negative, but somewhat species-specific, impact on tip moth parasitism.

Quantity and Ratio of Pheromone Components Among Multiple Generations of the Nantucket Pine Tip Moth (Lepidoptera: Tortricidae) in Georgia and Virginia

Abstract The quantity and ratio of two sex pheromone components in the abdominal gland of Rhyacionia frustrana (Comstock) were determined for three generations from the Georgia Piedmont, two generations from the Georgia Coastal Plain, and one generation from the Virginia Coastal Plain. There were no significant differences among quantities of either pheromone component among any generations or collection sites. Quantities for the major component, (E)-9-dodecen-1-yl acetate, varied among the samples from 10.8 to 18.6 ng per adult female. Similarly, quantities for the minor component, (E)-9,11-dodecadien-1-yl acetate, varied from 0.5 to 0.9 ng per female. Ratios were significantly different only between the second generation Georgia Coastal Plain and first-generation Virginia Coastal Plain, although we do not think these differences are biologically meaningful. Pheromone component ratios for the major and minor component ranged from 16.5:1–23.4:1 among all sites. The significance of these findings as they relate to synthetic bait efficacy and decreased summer trap catches of male R. frustrana is discussed.

Interspecific Variation in Host-Finding Cues of Parasitoids of the Southern Pine Beetle (Coleoptera: Scolytidae)'

Experiments were performed with host-associated olfactory attractants of the larval parasitoids of the southern pine beetle, Dendrocfonus frontal& Zimmermann, to elucidate both their biological origin and their chemical composition. Sticky-screen traps were erected in an active D. frontalis infestation and baited with parts of D. front&s-infested loblolly pines (Pinus taeda L.) or their extracts. The diversity of parasitoid species landing on trees infested with larval D. frontalis was substantially greater than that attracted to traps baited with wood and bark taken from similar, infested trees. Females of four parasitoid species, Spathius pallidus (Ashmead), Ropfrocerus xylophagorum (Ratzeburg), Dir~otiscus dendroctoni (Ashmead), and Euryfoma to- mici Ashmead, were attracted to bark infested with D. fro&a/is larvae. Two of these species, R. xylophagorum and S. pallidus, were attracted to debarked wood from host-infested trees al- though this tissue was free of hosts and host frass. Spafhius pallidus were more attracted to the excised bark (containing D. frontalis larvae and frass) than the debarked wood from D. frontalis- infested pine bolts, while R. xylophagorum were attracted in similar numbers to both materials. When traps were baited with steam/water-distilled extracts of D. frontalis-infested bark, R. xy- lophagorum strongly preferred extracts from bark containing earlyinstar larvae over extracts from bark infested with either younger (egg-stage) or older (late-instar larval and pupal) brood. In contrast, S. pallidus responded significantly only to extracts of late larval/pupal bark. Coupled gas chromatograph/mass spectrometer (GC-MS) analyses of the bark extracts revealed that the concentrations of numerous extract constituents correlated positively with trap catch of S. pal- lidus, but no such relationships were identified for R. xylophagorum. These data provide further evidence that members of the parasitoid complex associated with D. frontalis differ in their strategies for locating trees infested with susceptible hosts.