In 1980-81, teneral and fully melanized adult flea beetles were monitored with water traps. Phyllotreta cruciferae, P. striolata and Psylliodes punctulata are univoltine in southwestern Quebec. Their spatial distributions were estimated by D-Vac('(REGTM)) sampling in rutabaga and cabbage an the proportions of flea beetle species varied in time and space. Dispersal studies, using interception traps coupled with statistics of directional data, showed four immigrations to and seven emigrations from a rutabaga field. P. cruciferae was more attracted to allyl isothiocyanate than P. striolata, whereas the behavior of Ps. punctulata was not affected. Sex ratio estimations were affected accordingly. The color white significantly attracted more flea beetles than yellow, green and red. Overwintered adult flea beetles were more prevalent on later sown rutabaga, and the species proportions were slightly affected by the sowing date. Flea beetle infestations were simulated by punching out holes in cabbage seedlings.

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A systematic survey of the microbial and invertebrate natural enemies of Phyllophaga spp. was conducted from 1979 to 1981 in 45 localities in southern Quebec. Chronic but low (nonepizootic) rates of biotic regulation were found in all host life stages except eggs. The natural enemies included 36 species of predatory and parasitic insects, 15 mite species, six fungal species, five bacterial species, three different nematodes, one virus, one gordian worm, and one sporozoan. Microorganismal pathogenicities to white grubs were demonstrated by infectivity tests and laboratory bioassays using four methods of inoculation. Field-type microplot studies on the fungus Metarhizium anisopliae and the nematode Mikoletzkya aerivora were undertaken in 1982. The fungus and the nematode showed potential as biological suppressants of Phyllophaga grubs by causing 91% and 68% mortality, respectively. Twenty-seven chemicals were tested as attractants against P. anxia adults in 1981 in four localities in southern Quebec. Hexanoic acid was consistently the most attractive chemical to beetles of both sexes.

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The general objectives of this thesis project were to describe and to understand the dynamics creating occurrence patterns of saproxylic wood-feeding Coleoptera in snags (i.e., standing dead trees) of black spruce and aspen along the decay gradient. The first part of this thesis focuses on pre-landing host-selection behaviours in coniferophagous species, i.e. the use of host-produced volatiles to locate potential hosts. Results presented suggest that most saproxylic wood-feeding beetles studied herein use volatiles to orient towards potential habitat patches but that olfactive information does not allow the identification of suitable hosts at close range prior to landing. The second part of the thesis focuses on the occurrence patterns themselves and on underlying mechanisms. Sampling was conducted using snag dissection, a novel method allowing a better characterization of larval stage wood-feeding assemblages. Opposite patterns were observed between the two host species studied, as abundance and species richness were highest in early stages of decay in spruce, and in middle to late stages of decay in aspen. In aspen, numerous nutritional and physical parameters of dead wood correlated significantly with wood-borer occurrence. However, most of these parameters were strongly auto-correlated, and the explanatory model most highly ranked by model selection consisted of only a snag age term. Also, a simple neutral model based on temporal autocorrelation in occurrence probability produced patterns similar to those observed through sampling. In the last original paper presented, results suggest that wood-boring larvae select for specific types of substrate in highly variable aspen snags. This selection on the part of the larvae likely decreases the impact of the oviposition site on subsequent larval performance, and could explain the lack of strong selection seen on the part of the mother. My results suggest very different host-selection dynamics in black spruce and aspen, as assemblages of the former were dominated by early-decay species with volatiles-driven colonization dynamics, while middle- to late-decay species dominated the later, seemingly through mostly neutral colonization mechanisms. Some of my findings suggest that patterns observed in black spruce and aspen could be extrapolated to a coniferous/deciduous host dichotomy in colonization dynamics of woodfeeding species, based on divergent secondary chemistry and wood structure.

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No description available.

I examined saproxylic beetle responses in two silvicultural systems of the eastern mixedwood boreal forest of Quebec. I first investigated habitat-use and aspen-host use of saproxylic and bark and wood-boring beetles in remnant forest patches (cut-bock separators and small patches) left after harvest, theorized to resemble natural post-fire residual trees and snags. A second study focused on effects of partial cutting, a method that may serve to imitate natural succession dynamics. / Remnant forest patches had the highest saproxylic and bark and woodboring beetle species richness and relative abundance. Although non-significant, higher larval densities were also collected from remnant forest patches. In the second study, partial cut patches had an intermediate saproxylic beetle assemblage compared to uncut forest and clearcuts. / This research has brought new information on the effects of alternative harvesting practices on saproxylic beetles, supporting the hypothesis that biodiversity is best preserved based on forest management that is diversified and based on natural disturbance dynamics.