Evidence for divergence in cuticular hydrocarbon sex pheromone between California and Mississippi (United States of America) populations of bark beetle parasitoid Roptrocerus xylophagorum (Hymenoptera: Pteromalidae)

Roptrocerus xylophagorum (Ratzeburg) (Hymenoptera: Pteromalidae) is a common Holarctic parasitoid of the larvae and pupae of bark beetles (Coleoptera: Curculionidae: Scotytinae). In no-choice laboratory bioassays, we found that male wasps derived either from northern California or southwestern Mississippi, United States of America more frequently displayed sexual behaviours (including mounting, wing fanning, and copulation attempts) to glass bulb decoys treated with hexane cuticular washes of females derived from the same parasitoid population rather than the distant population. This result suggests that the composition of the cuticular hydrocarbon sex pheromone has diverged between eastern and western populations and is consistent with previous data indicating that R. xylophagorum may consist of more than one species.

Spruce beetle (Coleoptera: Scolytidae) parasitoids: cephalic morphology of larvae and a key to species (Hymenoptera: Braconidae, Pteromalidae)

Cast exuviae from final-instar larvae of four species of hymenopterous parasitoids of Dendroctonus rufipennis (Kirby, 1837) were examined for diagnostic characters. The head capsules of Bracon tenuis Muesebeck and Walkley, 1951, Coeloides rufovariegatus (Provancher, 1880), Roptrocerus xylophagorum (Ratzeburg, 1844), and Dinotiscus dendroctoni (Ashmead, 1894) each displayed unique combinations of characters allowing discrimination among species. Head capsules are illustrated, and a key to species is presented.

Host species influences body size and egg load of the bark beetle parasitoid Roptrocerus xylophagorum (Hymenoptera: Pteromalidae)

As early as 1844, it was stated that the size of the host may influence the size of parasitoid adults (Ratzeburg 1844) and that parasitoid size may affect fecundity (Salt 1941). Although positive relationships between host and parasitoid body size have been supported in the literature (Tillman and Cate 1993; Heimpel and Rosenheim 1995), this relationship is not universal to all host–parasitoid systems (King 1991; Morse 1994). Although the relationship between host size and body size of parasitoid adults has been observed for some bark beetle parasitoids (Bushing 1967; Samson 1984), the relationship between body size and fecundity has not been studied for bark beetle parasitoids. Roptrocerus xylophagorum Ratzeburg (Hymenoptera: Pteromalidae) is a bark beetle parasitoid with a wide host range that includes beetles in the genera Dendroctonus, Ips, and Scolytus (Bushing 1967).

Baseline egg load of southern pine beetle parasitoid complex

Egg load of newly emerged adult parasitoids of the southern pine beetle, Dendroctonus frontalis Zimmermann (Coleoptera: Scolytidae), was examined. Infested bark was collected from D. frontalis infestations in southwestern Arkansas (Clark and Montgomery counties; 1995), the Bankhead National Forest in Alabama (1999), and the Talladega National Forest in Alabama (1998–2000) between June and September of each collection year. Newly emerged parasitoid females were dissected and numbers of mature and immature eggs counted. There was no significant difference in number of eggs within a species and between parasitoids from the Bankhead National Forest compared with those from the Talladega National Forest in Alabama in 1999. There were differences in number of eggs within a species between years at the same location. Dendroctonus frontalis parasitoids in the family Pteromalidae (Hymenoptera) had the most mature eggs, followed by Braconidae (Hymenoptera) and Eurytomidae (Hymenoptera). Within the D. frontalis parasitoids in the family Pteromalidae, Dinotiscus dendroctoni (Ashmead) and Heydenia unica Cook and Davis had more mature eggs than did Roptrocerus xylophagorum Ratzeburg. Within the D. frontalis parasitoids in the family Braconidae, Meteorus hypophloei Cushman females contained the most mature eggs, followed by Dendrosoter sulcatus Muesebeck, Spathius pallidus Ashmead, and Coeloides pissodis (Ashmead). These data constitute a foundation for defining baseline egg load of the D. frontalis parasitoid complex.

THE ARRIVAL SEQUENCE OF THE ARTHROPOD COMPLEX FOLLOWING ATTACK BY DENDROCTONUS BREVICOMIS (COLEOPTERA: SCOLYTIDAE) IN PONDEROSA PINE

Continuous trapping on the bark surface of Dendroctonus brevicomis LeConte infested trees in the central Sierra Nevada mountains was undertaken with the objective of determining the spatial and temporal arrival patterns of the natural enemies and other insect associates of the western pine beetle. Over 100 species of D. brevicomis associates were collected and patterns of arrival were described for many of these. The main bark beetle predators were trapped during D. brevicomis mass arrival and shortly thereafter. Enoclerus lecontei, Temnochila chlorodia, and Aulonium longum, all predaceous beetles on D. brevicomis adults and larvae, were among the first species to arrive, as was Medetera aldrichii (Diptera), a larval predator. The bark beetle parasites Roptrocerus xylophagorum and Dinotiscus (=Cecidostiba) burkei (Hymenoptera) were well synchronized with the beetles’ life cycle as they arrived late in the beetles’ larval stages when suitable hosts were available.Approximately twice as many associates were trapped in the first (spring) beetle generation as in the second (fall). Differences between species with regard to height distribution were common, and these often varied with seasonal beetle generation.Calculations of changes in species diversity through time, of the associate complex trapped at the bark surface, were made for both the first and second beetle generation. Linear correlation analysis indicated a highly significant increase in species diversity occurred from the time of the beetles’ mass arrival until brood emergence. This increase may correspond to an increase in diversity of the structure of the subcortical community, as more insect species arrived and progressively modified the habitat of the newly killed tree.

NOTES ON THE BIOLOGIES OF HYMENOPTEROUS PARASITES OF IPS SPP. BARK BEETLES IN VIRGINIA

Biological data are given for Coeloides pissodis (Ashmead), Dendrosoter sulcatus Muesebeck, Heterospilus sp., Spathius pallidus Ashmead, Eurytoma conica Provancher, Cecidostiba polygraphi Ashmead, Heydenia unica Cook and Davis, Roptrocerus xylophagorum (Ratzeburg), Rhopalicus pulchripennis (Crawford), Rhopalicus tutela (Walker), and Tomicobia tibialis Ashmead. Only Coeloides pissodis was always closely associated with its host. The other larval parasites were often found disassociated from any host, suggesting an ability to seek out hosts in Ips galleries and the potential to attack more than one host. Observations indicated that pupal parasitism may be significant. Comment on the potential of some parasites as control agents is included.