Graduate Thesis Or Dissertation
 

Sound production in Leperisinus oregonous Blackman and L. californicus Swaine (Coleoptera:Scolytidae)

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  • Both Leperisinus oregonus and L. californicus are bark beetle species which emerge from Fraxinus latifolia brood logs as sexually immature adults and disperse to living ash. Occasional field observations suggest that, for overwintering and maturation feeding, L. oregonus enter trunks and branches, whereas L.; californicus enter twig crotches, buds and even leaf axils. Reemerged beetles also make these short burrows. Not only L. oregonus but also L. californicus initiate egg galleries April through June, and L. californicus adults that overwinter as larvae infest ash in August. Sex ratios of both species at emergence and also when trapped in the field to cages containing naturally infested logs were usually 1:1. In Sept. 1975, L. oregonus emergence varied with maximum daily temperature. L. californicus produced F-1 and F-2 generations in the greenhouse when provided with cut twigs and logs. Excisions of field attacks confirm previous reports that both species are monogamous and that females initiate gallery construction. The pars stridens, consisting of one file on the posterior medial undersurface of each elytron, showed bilateral, sex and species differences. The most notable were: left files shorter and wider than right files, females with fewer ridges than males, L. californicus with shorter files than L. oregonus. There was no species overlap in males' left file ridge spacing, averaging 1.9 μ for L. californicus and 3.0 μ for L. oregonus. Three-variable discriminant functions could completely separate the four species-sex groups. First principal components accounted for 47 to 68 percent of variation within species-sex-side groups. Left and right file measurements were correlated within species-sex groups, but redundancy was only 33 to 59 percent. Number of ridges was correlated with file length, even after the effect of elytral length was removed, within species-sex-side groups. The plectrum, a pair of scrapers on the seventh tergite's posterior edge, is absent in females. The distance between scrapers was slightly but significantly greater in L. oregonus than in L. californicus. In the laboratory, 25 of 50 L. californicus pairs mated while the male was on the bark surface at the female's gallery entrance, or partly inside the entrance. Based on 23 pairs, premating behavior averaged 16.4 min and copulation averaged 6.9 min. Most males of both species stridulated at conspecific female gallery entrances. In several instances, rival L. californicus males engaged in violent conflicts near attractive female galleries. In two cases, L. oregonus rivals gradually displaced resident males. Most male-male encounters were brief, and audiorecorded "rivalry" stridulation was similar to stress stridulation. Both were nearly continuous runs of short chirps. Premating and postmating stridulation consisted of intermittent series of longer chirps of alternating forms labelled "major" and "minor". Major chirps usually had similar numbers of toothstrikes but shorter durations and faster toothstrike rates than minor chirps. L. oregonus had faster series and premating chirp rates, shorter series durations, shorter minor chirp durations and fewer toothstrikes in both major and minor chirps than L. californicus. L. californicus had slightly but significantly faster chirp rates and shorter series durations after mating than before. Females were not heard to stridulate.
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