These first North American records for Polymerus cognatus (Fieber) from across Canada and the northeast United States, and P. vulneratus (Wolff) from northwest North America, indicate that the two species are naturally Holarctic. Diagnoses and dorsal habitus illustrations are provided to distinguish the taxa from other North American Polymerus species. An argument for considering P. balli Knight, P. cognatus, P. elegans (Reuter), P. flaviloris Knight, P. froeschneri Knight, and P. vulneratus a monophyletic species-group is presented.

Eight species of the siphonine genus Actia Robineau-Desvoidy are recognized in the Nearctic Region, including four that are new: A. dasymyia sp.nov. (type-locality 21 mi. east Tuktoyaktuk, North West Territories, Canada), A. dimorpha sp.nov. (type-locality Sapelo Island, Georgia, USA), A. radialis sp.nov. (type-locality Gatineau Park, Quebec, Canada), and A. sternalis sp.nov. (type-locality mi. 51 Dempster Highway, Yukon, Canada). Adults of the eight species are keyed, described, illustrated (heads, wings, and male terminalia), and their distributions mapped. The species are arranged into three species groups: the autumnalis-group with Nearctic members A. autumnalis (Townsend), A. rufescens (Greene), A. diffidens Curran, and A. dimorpha sp.nov.; the lamia-group with Nearctic members A. interrupta Curran, A. dasymyia sp.nov., and A. radialis sp.nov.; and the crassicornis-group with the single Nearctic member A. sternalis sp.nov. Nearctic Actia are inferred to be of relatively recent origin because only the A. autumnalis/A. rufescens species pair seems to have speciated within the Nearctic Region. Actia autumnalis/A. rufescens, A. diffidens, and A. dimorpha are each hypothesized to have their closest phylogenetic affinities with Neotropical species, and A. sternalis, A. interrupta, A. dasymyia, and questionably A. radialis are each hypothesized to have their closest affinities with Palearctic species.

The Nearctic species of the genus Duta are revised. Two new species are described: D. foveolata (Canada, USA) and D. policeps (Canada, USA). Duta virginiensis (Ashmead), new combination, is shown to be widely distributed in the Western Hemisphere, extending to the New World tropics. A diagnosis of Duta and a key to the Nearctic species are given. The impact of environmental degradation on the frequency of Duta species in North America is discussed.

Adults of Bandakia hoffmannae sp.nov., Bandakia mexicana sp.nov., Chappuisides notialis sp.nov., and Neoacarus adocetus sp.nov., all collected in the mountains west of Mexico City, are described. These are the first reports of species of these three essentially holarctic genera from south of the United States border in North America. These discoveries provide new insight concerning the extent of refugial areas for freshwater arthropods in southern North America during the Pleistocene.

Adult females of Rutripalpus canadensis sp.nov. (family Rutripalpidae) from Cape Breton Island, Nova Scotia, Canada, adults of both sexes of Scutolebertia trinitensis gen.nov., sp.nov. (family Lebertiidae) from the Coast Range in northern California, USA, and adults of both sexes of Pseudotorrenticola chiricahua sp.nov. (family Torrenticolidae) from Arizona, USA, are described. The three new species represent the first members of their respective genera to be reported from North America, and their discovery provides new perspectives on the phylogeny and biogeography of mites in these genera.

Dilemmas in weed biocontrol are wide ranging. Even the term biological control is confusing as meanings may be restricted to the use of parasites and predators or extend to the use of all non-chemical means of control. Another problem is that two-thirds of the agents released do not become numerous enough to inflict major damage to the weed population, although this statistic is misleading as it includes agents costing little in pre-release studies where failure is of little consequence and those costing about two scientist years each, or currently about $400,000. Many of the suggestions for improvement are costly and time consuming. Delay is unacceptable where agent release is seen by sponsors as a mark of progress in a program likely to require 20 years and funding is difficult. Analysis of previous biocontrol attempts for attributes of "success" have been disappointing, partly because there are a number of steps involved, each with its own attributes. This paper recognizes four graded "success" steps and discusses many agent selection methods.

There are public demands for a change in emphasis from chemical to biological control; but in the absence of effective enabling legislation, the practice of biocontrol can be legally and politically hazardous; biocontrol should be carried out by a multidisciplinary team but it is usually assigned to a single scientist; it needs to branch in new directions to remain scientifically stimulating, but this increases the risk of failure. Possible solutions for these dilemmas are discussed.

The impact of canopy dieback on the activity and diversity of epigeal Carabidae was studied during the summers of 1987 and 1988 in 18 maple stands in southeastern Québec, using pitfall traps. A canopy thinning index (CTI) based on severity and incidence of dieback, and on tree basal area was calculated for each of the 72 stations sampled. An analysis of variance shows that canopy dieback had a significant effect on carabid beetle activity in 1988. The CTI was negatively correlated with the carabid species richness and diversity in 1988. The number of individuals caught per station was negatively correlated with the CTI for all species combined, except for the dominant Pterostichus coracinus Newm. in 1988. These results indicate a negative response of carabid beetles to canopy dieback in 1988; the climate may have tempered the effects of dieback in 1987.

The effects of root damage by larval cabbage maggots, Delia radicum (L.), on yield of canola, Brassica campestris L., were examined in laboratory experiments. Inoculations of eggs or first-instar larvae resulted in significant root damage. Damage that exceeded 50% of taproot surface area resulted in fewer racemes, fewer productive seed pods on axillary racemes, lower total biomass, and reduced yield of seed. Despite the latter effect, damage that restricts the number of flowering racemes and induces abortion of seed on axillary racemes may increase the efficiency of yield in canola, which flowers indeterminately over a short growing season.

The probing behavior of the potato aphid, Macrosiphum euphorbiae (Thomas), is significantly different on potato than on tobacco plants. The higher frequency of short-duration probes, ideal for the transmission of nonpersistent viruses, is the apparent cause for the higher rate of potato virus Y° (PVY°) transmission on tobacco than on potato. However, experimental augmentation of short inoculation probes by M. euphorbiae on potato and tobacco failed to increase PVY° transmission on either. These results demonstrate the absence of a causal relationship between variations in probing behavior of M. euphorbiae and variations in the transmissibility of PVY° by this vector on tobacco and potato.

Six new species of Mucroseius having adult females phoretic on adult sawyer beetles of the genus Monochamus are described: Mucroseius nipponensis and Mucroseius squamosus from Monochamus alternatus Hope in Japan, Mucroseius algonquian from three species of Monochamus in eastern Canada and eastern United States, Mucroseius disparisetus from Monochamus titillator (Fabricius) in southeastern United States, Mucroseius Californicus from Monochamus clamator (LeConte) in California, and Mucroseius mexicanus from Monochamus rubigineus (Bates) in Mexico. Mucroseius aciculatus (Ishikawa, 1968), new combination, from Mecynippus pubicornis Bates in Japan, and the type-species, Mucroseius monochami Lindquist, 1962, from several species of Monochamus widely distributed in North America, are redescribed. Misidentifications of these species in the Japanese and North American literature are noted, and a key is given for these eight species. One adult female of an undescribed species found on a sawyer, Monochamus sutor Linnaeus, from Europe, is noted as possibly belonging to Mucroseius.

The taxon Mucroseius is redescribed, and its problematic status as a genus is reviewed. The phylogenetic position of Mucroseius, which appears to be derived within the genus Proctolaelaps, is discussed. Previous observations on biological and ecological aspects of Mucroseius mites, including those published in Japanese, are critically reviewed, with new data added for host ranges and specificities, distribution, phoretic behavior, occurrence in sawyer gallery systems, mode of reproduction, and their association with the pine wood nematode, Bursaphelenchus xylophilus (Steiner and Buhrer) Nickle. Cheliceral structure and speculations on the feeding habits of these mites are discussed; however, feeding preferences have not been clarified.