Dosdall, L. M., Florence, L. Z., Conway, P. M. and Cowle, N. T. 1998. Tillage regime, row spacing, and seeding rate influence infestations of root maggots (Delia spp.) (Diptera: Anthomyiidae) in canola. Can. J. Plant Sci. 78: 671-681. Infestations of root maggots (Delia spp.) (Diptera: Anthomyiidae) were assessed in Brassica rapa L. and Brassica napus L. grown under conventional and zero tillage regimes, at three row spacings (10, 20 and 30 cm) and three seeding rates (5.0, 7.5 and 10.0 kg ha -1 or 120, 180 and 240 plants m -2 ). The studies were conducted during two growing seasons (1995 and 1996) at each of two sites in central Alberta. Root maggot infestations were assessed by determining the numbers of eggs laid per plant during the growing season and by larval feeding damage to canola taproots assessed at the end of the season. Seed yields of the treatment plots also were determined. Plants of B. rapa were significantly more susceptible to root maggot infestations than were plants of B. napus. Root maggot egg populations and root damage were generally greater with zero tillage than with conventional tillage. Plants grown at higher seeding rates (7.5 and 10.0 kg ha -1 ) usually had less root damage than plants grown at the lowest (5.0 kg ha -1 ) seeding rate, and canola grown at wider row spacings (20 and 30 cm) had less root damage and higher yields than canola grown at the narrowest spacing (10 cm). Response surface regression analyses determined that deposition of fewest root maggot eggs per plant, least root damage and maximum yields occurred at seeding rates ranging from 7 to 11 kg ha -1 and at row spacings ranging from 17 to 25 cm. Even though canola grown in zero tillage had greater root maggot infestations than canola grown in conventional tillage, higher yields still occurred with zero tillage. Zero tillage is therefore an appropriate agronomic practice in areas infested by high populations of root maggots. Sowing B. napus rather than B. rapa, increasing seeding rates and widening row spacings are also appropriate cultural control practices for reducing crop damage from these pests. Les analyses de régression de la surface de réponse ont servi à déter-miner que les pontes de la mouche les moins abondantes par plantes, les endommagements racinaires les plus bénins et les rendements maximums survenaient à une densité de semis allant de 7 à 11 kg ha -1 et à des largeurs de l'interligne se situant entre 17 et 25 cm. Même si le semis direct donnait lieu à des infestations plus graves que le travail classique, il gardait encore l'avantage sur ce dernier sur le plan du rendement. Il demeure donc une pratique agronomique convenable dans les zones de fortes infestations par la mouche des crucifères. L'utilisation de B. napus plutôt que de B. rapa, l'accroissement de la densité de semis et l'élargissement de l'interligne sont d'autres bonnes techniques culturales de prévention des dégâts causés par ce ravageur.

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Dispersal behavior of the southern pine beetle, Dendroctonus frontalis Zimmermann (Coleoptera: Scolytidae), in response to synthetic aggregating pheromone (frontalin) indicates an exponential decrease in response with distance from the site of emergence. Differential response during dispersal among genotypes at a polymorphic esterase locus was found by using starch gel electrophoresis. These differences produced allelic distributions that predict increased genetic diversity concurrent with increasing dispersal distance from the source population.

A spontaneous epidemic of nephritis among young rabbits associated with a protozoan parasite has been observed in a certain breeding stock since 1918. It is regarded as a nest infection. The parasite is tentatively classed among the microsporidia and the stages encountered are regarded as vegetative which may perhaps pass through several generations in the same host. It is a parasite of the epithelial cell, provoking no immediate host reactions. These are supposed to follow injury such as destruction of the epithelium and denudation and plugging of the tubules. The localizations in the brain are also without cell reaction, except under special conditions, and the many cell foci present are attributed to coccidia and perhaps bacteria and other intestinal parasites. The kidneys are looked upon as the normal habitat and the brain parasites as aberrant and outside the normal cycle unless it can be shown that the spores discharged into the circulation may again multiply in some organ like the kidneys in direct communication with the exterior. It is highly probable that many reported cases of nephritis among older rabbits used in experiments had their origin in an early invasion of the parasite described.

Azotobacter spp., Azospirillum spp., and Desulfovibrio spp., were identified as the predominant nitrogen-fixing bacteria associated with seedling root sections collected from natural stands of Pinusbanksiana Lamb., Piceamariana (Mill.) B.S.P., and Larixlaricina (Du Roi) K. Koch growing in Alberta. Samples from the sandy upland habitat of P. banksiana exhibited lower average rates of nitrogen fixation relative to the wet lowland occupied by P. mariana and L. laricina. Average nitrogen-fixing capacity (by acetylene reduction) was greater among bacteria isolates from L. laricina than those from P. mariana. Azospirillum spp. were strongly associated with P. mariana, while Azotobacter spp. were isolated more frequently from L. laricina.