Semiochemical Interactions between Scolytus ventralis LeConte and Pityokteines elegans (Swaine) (Coleoptera: Scolytidae)

Two experiments evaluated the effect of baiting uninfested grand fir logs and trees undergoing initial attack by Scolytus ventralis LeConte with Pityokteines elegans (Swaine) pheromone, on the subsequent attack by both species. Two more experiments assessed the effect of synthetic bark oil, exo-brevicomin, and P. elegans pheromone on the response by each species to multiple-funnel traps baited with attractants for the other species. The pheromone of P. elegans on unattacked logs did not have an inhibitory effect on the attack by S. ventralis. However, trees attacked by S. ventralis that were baited with P. elegans pheromone just after attack, yielded significantly fewer S. ventralis progeny than the unbaited controls. Neither synthetic bark oil nor exo-brevicomin caused a significant change in the catch of P. elegans in traps baited with its pheromone, but the predator Thanasimus undatulus Say was caught in traps baited with (±)-ipsenol, (±)-ipsdienol and synthetic bark oil, and another predator, Enoclerus sphegeus F., was caught in traps baited with exo-brevicomin alone or in combination with ipsenol and ipsdienol. The results do not support the hypothesis that interference competition based on semiochemical communication occurs between the two species.

EFFECTIVENESS OF THE DOUGLAS-FIR BEETLE ANTIAGGREGATIVE PHEROMONE METHYLCYCLOHEXENONE AT THREE CONCENTRATIONS AND SPACINGS AROUND FELLED HOST TREES

The antiaggregative pheromone 3-methyl-2-cyclohexen-1-one (MCH) of the Douglas-fir beetle (Dendroctonus pseudotsugae Hopk.) was diffused at three rates and three spacings around attractive felled trees. Optimum treatment was ca. 1–2 mg/day at 10-ft spacing (0.06–1.3 g/acre per day), which reduced Douglas-fir beetle attacks and progeny by 96% and 91%, respectively. Progeny in trees exposed to higher than optimum MCH concentration were less mature, but not significantly fewer than progeny in controls. Densities of immature stages of nine other taxa of insects, both entomophagous and commensal, were determined. Abundance of larvae of the predacious clerids Enoclerus sphegeus Fab. and Thanasimus undatulus Say was significantly correlated with abundance of Douglas-fir beetle attacks and progeny. The predator Temnochila chlorodia (Mann.) and the associate Pseudohylesinus nebulosus (Lee.) were more dense on samples in the test area where Douglas-fir beetle population and damage were lowest. Density of the dipterous predator Medetera aldrichii (Wheeler) was correlated with numbers of beetle entrances, but decreased at high MCH concentrations. Abundance of Coeloides brunneri Vier., a braconid parasite, was correlated with numbers of beetle brood. Presence of MCH appeared to increase abundance of the associate Pissodes fasciatus Lec. and modify its distribution in trees. Use of methylcyclohexenone for preventing infestation of susceptible trees is a potential control strategy, but a more practical and effective formulation must be developed.

PREY CONSUMPTION AND VARIATIONS IN LARVAL BIOLOGY OF ENOCLERUS SPHEGEUS (COLEOPTERA: CLERIDAE)

Larvae of Enoclerus sphegeus Fabricius (Coleoptera: Cleridae) were separated into three groups for study. Throughout their development, the larvae in each group were fed mountain pine beetle larvae, Dendroctonus ponderosae Hopkins (Coleoptera: Scolytidae), of a specific size (small, medium, or large). Clerid larvae fed small D. ponderosae larvae generally completed three stadia, while the other two groups, which were fed medium-sized and large prey, respectively, usually passed through two larval stadia. The number of stadia a larva would have was determined by the amount of food consumed during the first stadium. The feeding period of larvae given small prey was considerably longer than that of those fed medium-sized or large beetle larvae, but the prepupal period was much shorter. The head capsules of second-instar larvae that passed through two stadia were distinctly wider than those of second-instar larvae that completed three stadia.

ENOCLERUS SPHEGEUS (COLEOPTERA: CLERIDAE), A PREDATOR OF DENDROCTONUS PONDEROSAE (COLEOPTERA: SCOLYTIDAE) IN THE BLACK HILLS

Enoclerus sphegeus Fabricius adults were most abundant on trees infested with Dendroctonus ponderosae Hopkins in May and June of 1966 and 1967. Greatest numbers of adults were observed on the bole from 0 to 5 ft aboveground, apparently in response to the activity of other scolytids. In the laboratory, each adult killed about 1 D. ponderosae per day, and each larva killed about 25 D. ponderosae during development. Mean larval densities were generally less than 0.2 per square foot at four different sampling heights on the tree bole during the overwintering period. Densities were greatest at all heights in July. Maximum larval density was observed at the 1.5-ft height. Larvae began leaving the trees for pupation sites in July of both years. It is estimated that adult clerids consume less than 1% of the adult beetle population during their attack period and the clerid larvae kill 5–11% of the beetle brood.

The Bark Beetle Complex Associated with Lodgepole Pine Slash in Alberta: Part III—Notes on the Biologies of Several Predators with Special Reference to Enoclerus sphegeus Fab. (Coleoptera: Cleridae) and Two Species of Mites

The most important predators found with broods of Ips pini (Say) and Ips perroti Sw. belong to the orders Coleoptera, Diptera, Hemiptera, and Acarina.Among the Coleoptera, Enoclerus sphegeus Fab. was the most aggressive and responsible for the greatest predation. The small clerid, Thanasimus undulatus Say, was present in the area but rarely encountered. Dipterous predators included Loachea corticis Taylor, Oscinella sp. nr. magnipalpus Beck. and Medeterus modestus Van Duzee. A hemipterous egg predator, Anthocoris musculus Fall. was found occasionally within the main Ips galleries.