John W. Peacock

Chemical attractants for the smaller European elm bark beetle Scolytus multistriatus (Coleoptera: Scolytidae).

The secondary attractant for the smaller European elm bark beetleScolytus multistriatus is a mixture of three compounds: (-)4-methyl-3-heptanol(I); 2,4-dimethyl-5-ethyl-6,8-dioxabicyclo(3.2.1) octane (II); and (−)α-cubebene (III). The novel structure assigned to compound II was confirmed by synthesis. All three compounds were isolated from the volatile compounds collected on Porapak Q by aerating elm bolts infested with virgin female beetles. The GLC fractionations were monitored by two laboratory bioassays. Individually, each compound was inactive in the laboratory bioassays, but a mixture of all three showed activity nearly equivalent to that of the of the original Porapak extract. A mixture of synthetic I and II plus natural III (from cubeb oil) was highly attractive to beetles in preliminary field tests.

Response of the European elm bark beetle,Scolytus multistriatus (Coleoptera: Scolytidae), to isomers and components of its pheromone

Laboratory bioassays (two methods) and field tests demonstrated synergistic action of the three components [(−)-4-methyl-3-heptanol (I); (−)-2,4-dimethyl-5-ethyl-6,8-dioxabicylo[3.2.1]octane (α-multistriatin) (II); and (−)-α-cubebene (III)] of the pheromone bouquet ofScolytus multistriatus. Individually and in pairs the components were slightly attractive; I+II was clearly the most active doublet. Indirect evidence indicates that only one of the four enantiomers of I is active. Of the α, β, γ and δ isomers of II, only the α is active. With the addition of compound I, slightly attractive extract from mated females became nearly as active as extract from virgin females.

Collection on Porapak Q of the aggregation pheromone ofScolytus multistriatus (Coleoptera: Scolytidae)

The attractive volatiles in the air around the virgin female of the smaller European elm bark beetle,Scolytus multistriatus (Marsham), tunneling in elm logs can be collected by passing the air through a column of Porapak Q. These volatiles can be removed from the Porapak by Soxhlet extraction with hexane, yielding an extract that is attractive to in-flight beetles in the field. GLC analyses of this extract and an extract of virgin female frass indicate that the aeration extract contains active chemicals that are not in the extract of frass.

Response of the elm bark beetle,Scolytus multistriatus (Coleoptera: Scolytidae), to component mixtures and doses of the pheromone, multilure

The response of the elm bark beetle,Scolytus multistriatus (Marsham), was measured to various doses and mixtures of the three components of its aggregation pheromone. The ratio of the components released, particularly heptanol to multistriatin, strongly influenced the number, but not the sex ratio, of beetles that responded. We concluded that a bait that released about 400∶ 100∶ 800 μg/day of heptanol-multistriatin-cubebene would be effective in mass-trapping beetles.

An estimate of the effectiveness of pheromone-baited traps for the suppression ofScolytus multistriatus (Coleoptera: Scolytidae)

We attempted to suppress a population ofScolytus multistriatus (Marsham), the principal vector of Dutch elm disease, by trapping flying beetles on sticky traps baited with synthetic pheromone. The estimated catch on 421 traps distributed throughout a 1-km2 plot in Detroit, Michigan, was nearly 1 million beetles. Because an estimated 5 million beetles emerged in the plot during the study period, we conclude that this preliminary trapping study had no appreciable effect on suppressing the population. Studies that employ improved materials and techniques are continuing.

Deployment of Traps in a Barrier Strategy to Reduce Populations of the European Elm Bark Beetle, and the Incidence of Dutch Elm Disease

Dutch elm disease (DED) is caused by a fungus, Ceratocystis ulmi (Buisman) C. Moreau, that infests the vascular systems of elms and forms sticky masses of conidial spores (coremia) in cavities under the bark of the diseased portions of the tree. These spores have been detected on many arthropods that are found beneath the bark of diseased elms, but only bark beetles are an efficient vector because only they frequently visit or inflict wounds in healthy elms deposition of spores in wounds is necessary for infection.