We compared the insect and arachnid species found in spring and summer samples of necrotic tissue of three species of columnar cacti, cardón [Pachycereus pringlei (S. Watson) Britten and Rose], organ-pipe (Stenocereus thurberi Buxb.), and senita [Lophocereus schottii (Engelm.) Britten and Rose] (all Cactaceae), endemic to the Sonoran Desert of North America. A total of 9380 arthropods belonging to 34 species, 23 families, 10 orders, and 2 classes were collected in 36 samples. Arthropod communities differed in composition among host cacti, as well as between seasons. These differences may be a function of variation in host characteristics, such as chemical composition and abiotic factors, such as water content or temperature.

The Diptera are the second most important order among flower-visiting (anthophilous) and flower-pollinating insects worldwide. Their taxonomic diversity ranges from Nematocera to Brachycera, including most families within the suborders. Especially important are Syrphidae, Bombyliidae, and Muscoidea. Other families, especially of small flies, are less appreciated and often overlooked for their associations with flowers. We have compiled records of their flower visitations to show that they may be more prevalent than usually thought. Our knowledge of anthophilous Diptera needs to be enhanced by future research concerning (i) the significance of nocturnal Nematocera and acalypterate muscoids as pollinators, (ii) the extent to which the relatively ineffective pollen-carrying ability of some taxa can be compensated by the abundance of individuals, and (iii) the role of Diptera as pollinators of the first flowering plants (Angiospermae) by using phylogenetic and palaeontological evidence. Specializations in floral relationships involve the morphology of Diptera, especially of their mouthparts, nutritional requirements, and behaviour, as well as concomitant floral attributes. The South African flora has the most highly specialized relations with dipterous pollinators, but in arctic and alpine generalist fly–flower relations are important in pollination and fly nutrition.

A fossil mayfly nymph Caenoephemera shangyuanensis, gen.nov., sp.nov., discovered in the lower part of the Upper Jurassic – Lower Cretaceous Yixian Formation of Jianshangou, Beipiao district, West Liaoning, China, is described. It has several archaic features typical of Paleozoic mayfly nymphs, such as 5 tarsal segments and hind wing pads not covered by fore wing pads, but also exhibits specialized modern features, such as a short metathorax, abdominal tracheal gills, and cerci. It appears to be intermediate in structure between Paleozoic and extant mayfly nymphs.

The Canadian species of the genus Placusa Erichson are reviewed. Eight species are recorded, of which four constitute new Canadian records (P. despecta Erichson, P. incompleta Sjöberg, P. petulans Casey, and P. vaga Casey) and two are new to science (P. pseudosuecica Klimaszewski sp.nov., and P. canadensis Klimaszewski sp.nov.). Placusa turbata Casey, one of the two species previously recorded from British Columbia, is here considered a synonym of P. tachyporoides (Waltl) and is reported for the first time from eastern Canada (New Brunswick, Ontario, Quebec). New data are provided on the systematics, distribution, bionomics, and relationships of selected North American species. A key to the species occurring in Canada is presented with illustrations of the median lobe of the aedeagus, spermatheca, male tergite 8, antennae, and outline drawings of the head and adult forebody for each species. Selected Palearctic species are also illustrated for easy comparison with the closely related Nearctic species. The Canadian distribution is presented on contour maps, and world distribution is discussed for all species. The following lectotypes are designated for the Nearctic species which were described from more than one specimen without former holotype designation: Casey (1893, 1911): P. frosti, P. strata, P. tacomae, P. turbata; Erichson (1840): P. despecta; and Sachse (1852): Oxypoda minuta Sachse. Oxypoda minuta is transferred to the genus Placusa and newly synonymized with P. despecta Erichson (1840).

The last instar and pupa of Pyropyga nigricans (Say, 1823) are described, illustrated, and compared to those of Pyropyga modesta Green, 1961; these species differ in the color pattern of the pronotum and abdominal tergites, and the morphology of the maxilla and labium. Larvae of the genus Pyropyga Motschulsky, 1852 are compared to those of the genera Lamprohiza Motschulsky, 1853, Lucidota LeConte, 1833, and Phosphaenus Laporte, 1833 (all belonging to the tribe Photinini but to different subtribes); on the basis of general body shape and morphology of the head capsule, antennae, and mouthparts, larvae of the genus Pyropyga seem more closely related to those of the genus Lucidota than to those of the other two genera.

The diversity of Agromyzidae (Diptera) associated with disjunct xeric grasslands was studied at six south-facing slopes in the southern Yukon Territory, Canada. Agromyzidae was the most diverse of 32 families of Brachycera at the sites, with 34 species (485 specimens) collected. Eight new species are described: Liriomyza naressp.nov., Metopomyza adretanasp.nov., Phytoliriomyza depriceisp.nov., Phytoliriomyza triangulatasp.nov., Phytomyza conglomeratasp.nov., Phytomyza dionisp.nov., Phytomyza klondikensissp.nov., and Phytomyza takhiniensissp.nov. Twenty previously described species were identified and six other unnamed species were represented by females only. Fourteen of the 20 previously described species are recorded from the Yukon for the first time; ecological and systematic notes are given for each species. Although the vegetation of the sample sites was often similar, there were pronounced differences in the species assemblage of Agromyzidae collected at each site. Thirteen of the previously known species are widespread in the Nearctic region (including Holarctic species), six species are restricted to the western Nearctic, and one species is known from the Palaearctic and western Nearctic. Several major range extensions are noted.

Sexual size dimorphism occurs in many species. Differences between males and females, in size or other characteristics, may result from sexual selection, fecundity selection, natural selection, non-adaptive processes, or a combination of these pressures (Darwin 1874; Selander 1966; Trivers 1976; Slatkin 1984; Shine 1989). In insects, females with large body size often produce more eggs than smaller females, and femalebiased sexual size dimorphism is commonly attributed to such fecundity selection (e.g., Preziosi and Fairbairn 1997; but see Leather 1988). Water boatmen are detrivorous or zoophagous aquatic insects often inhabiting small ponds of the Northern Hemisphere (Hungerford 1948; Nosil and Reimchen 2001). Female water boatmen are generally larger than males. In this note, I quantify the nature and magnitude of a previously undescribed sexual size dimorphism in a natural population of the water boatman Callicorixa vulnerata Uhler (Hemiptera: Corixidae). I tested for differences between males and females in mean trait size (body length, body weight, mid-leg tarsal length, mid-leg tarsal spine number), and also tested for sexual dimorphism in allometric relationships between tarsal traits and body length.

Three new species of oribatid mites in two genera of Mycobatidae are recorded from canopy habitats of coniferous temperate rainforest and montane forest in the Pacific Northwest of North America. These species, Mycobates acuspidatussp.nov., M. corticeussp.nov., and Zachvatkinibates epiphytossp.nov., are described on the basis of adults and immatures. The previous key for adult Mycobates species of America north of Mexico is modified to include these new species, and a key for adults is given for the three species of Zachvatkinibates now known from North America.

The Holarctic Scopula cajanderi (Herz) species group is revised on the basis of external and genitalic characters. The taxa included in the species group are Scopula cajanderi (Herz, 1903 [not 1904]) (= the Palaearctic Scopula elwesi sajanensis Prout, 1935 syn.nov., = the Palaearctic Scopula elwesi achlyoides Prout, 1935 syn.nov., = the Nearctic Scopula septentrionicola McDunnough, 1939 syn.nov.), thus making S. cajanderi Holarctic; Scopula mustangensis Yazaki, 1995; and Scopula aegrefasciatasp.nov. Lectotypes are designated for the following species which were described from more than one specimen without holotype designation: S. cajanderi, Scopula anaitaria (Herz, 1903), and S. e. achlyoides. The systematic position of Scopula elwesi elwesi Prout, 1922 within the genus Scopula is uncertain. A key to the species is presented with illustrations of the adults and genitalia, and a distribution map is presented for all taxa. An examination of the biogeography of S. cajanderi suggests that the Wisconsinan and Sartan glaciations may have played a part in the origin of the disjunct populations.

Five species of Trichomalopsis Crawford associated with Haematobia irritans (L.) (horn fly), Musca domestica L. (house fly), Musca autumnalis DeGeer (face fly), and Stomoxys calcitrans (L.) (stable fly) in North America are reviewed. The species Trichomalopsis americana (Gahan), Trichomalopsis dubia (Ashmead), Trichomalopsis sarcophagae (Gahan), Trichomalopsis tachinae (Gahan), and Trichomalopsis viridescens (Walsh) are described, keyed, and differentiated from other recognized North American species. Lectotypes are designated for T. dubia, T. sarcophagae, and T. tachinae. Distribution and host associations are recorded for the species. Trichomalopsis americana and T. viridescens are newly recorded as parasitoids of M. domestica; T. dubia and T. sarcophagae are also newly recorded as parasitoids of Hypoderma lineatum (Villers) (common cattle grub) and Hypoderma bovis (L.) (northern cattle grub), respectively. Some previously published host associations and parasitoid identifications are corrected based on examination of voucher specimens. The known biology of each species is reviewed. The presence of Trichomalopsis albipilosa (Gahan) in North America is considered to be erroneous based on a misidentification of T. americana.

Descriptions are presented of larval instars of three species of the colymbetine tribe Matini Zimmermann (Coleoptera: Dytiscidae), Batrachomatus daemeli (Sharp), Matus bicarinatus (Say), and Allomatus nannup Watts, including a chaetotaxic and porotaxic analysis of the cephalic capsule, head appendages, legs, last abdominal segment, and urogomphi. A parsimony analysis based on 32 informative larval characteristics was conducted with the computer program NONA. Members of the Matini are postulated to share a monophyletic origin based on (i) seta TR2 articulated anteroventroproximally on the trochanter; (ii) seta TR5 elongate on the metatrochanter; (iii) seta TA1 elongate and inserted proximally on the tarsus; (iv) antenomere III with a hole-like ventroapical spinula; (v) prementum with the primary setae LA2, LA3, LA4, LA5, and LA8 spine-like and elongate; (vi) presence of secondary setae on the cephalic appendages; and (vii) presence of additional primary setae on the last abdominal segment. A clade Matini + Colymbetini is postulated based on (i) metafemoral seta FE5; (ii) metafemoral seta FE6; (iii) seta TI6 on tibia, all elongate and hair-like; (iv) one-segmented urogomphus; (v) presence of an occipital suture in first instar; (vi) galea elongate; (vii) presence of natatory setae on legs; and (viii) presence of secondary setae on the urogomphus.

Antanambecoris pronotalisgen.nov., sp.nov., and Pluotenia pullagen.nov., sp.nov., are described from specimens collected in Madagascar and belonging to the old world tribe Acanthocorini. Dorsal habitus, male genital capsule, and parameres are illustrated and a key to the malagasy genera is provided.

The genus Holocephalus Hope is revised and now contains five species: H. cristatus (Gillet), H. eridanus (Olivier), H. julienisp.nov., H. sculptus (Gillet), and H. simonisp.nov. All taxa are described and illustrated. A key to species of Holocephalus is included. Lectotypes are designated for H. eridanus and H. sculptus. Scarabaeus eridanus Olivier is designated as the type species for the generic name Atrichius Gillet (a junior synonym of Holocephalus).

The levels of ovarian growth and transcription of the vitellogenin gene were compared in Pissodes strobi Peck (Coleoptera: Curculionidae) feeding on severed leaders from susceptible and resistant Picea sitchensis (Bong) Carr (Pinaceae) and in weevils given a dose of an aqueous extract from the bark of such leaders. A force-feeding method was developed to deliver the extracts into the alimentary canal of the weevils. Weevils given one dose of the aqueous extract from resistant leaders, followed by feeding on sections of laterals from susceptible trees, exhibited a 60% inhibition of oocyte growth relative to insects given the extract from susceptible leaders. In similar experiments, transcription of the vitellogenin gene of the weevils was inhibited by about 48%. Transcription of the vitellogenin gene was reduced by about 60% in weevils feeding on the severed leaders from the resistant clone relative to those feeding on severed leaders from susceptible trees. Results indicate that these effects of resistance do not require an intact tree. Experiments using extracts show that the observed effects result from a post-ingestive effect of the extract.

The Neotropical genus Acanthoscelio Ashmead is revised. We recognize eight species, found from Costa Rica south to Paraguay and southeastern Brazil. Acanthoscelio americanus Ashmead (Brazil) and A. flavipes Ashmead (Costa Rica, Panama, Venezuela, and Trinidad) are redescribed, and six new species are described: A. acutussp.nov. (Costa Rica, Colombia, Venezuela, Trinidad, Ecuador, Peru, and Brazil), A. latenssp.nov. (Ecuador), A. nimbosussp.nov. (Colombia, Ecuador, Peru, Brazil, and Bolivia), A. prolatussp.nov. (Colombia and Ecuador), A. punctatussp.nov. (Costa Rica, Panama, Colombia, and Ecuador), and A. radiatussp.nov. (Colombia, Ecuador, Peru, Brazil, and French Guiana). A key to species is provided.

The species Phtheiropoios centralissp.nov. is described and illustrated from specimens collected on an undescribed species of Ctenomys from Rio Quinto, central Córdoba Province, Argentina. Diagnostic features for the new species include proportion of the male forficula, male external genitalia, and counts of setae and body measurements in both sexes. Its morphological affinities with other species and a key to males of all species of the genus Phtheiropoios known to parasitize rodents of the genus Ctenomys are included.

A comparison of appressed teeth-like structures, coined tempers, on the flagellum of the male internal sac among 10 North American and one Asian species of tiger beetles is consistent with earlier proposed genera of Cicindela Linné, ranked here as subgenera. Based on scanning electron photomicrographs, observations revealed that the flagellum has a single groove along its whole length, with tempers in the groove, and for most species tempers are present only on one side of the ungrooved flagellar surface; tempers point basally (proximally) both on the flagellar surface and within the flagellar groove; and a distributional pattern of the tempers appears to be unique to each subgenus. The species Cicindela punctulata Olivier and Cicindela lepida Dejean have a lumen in place of a flagellar groove, the former with tempers on the ungrooved flagellar surface and the latter without. Tempers on the ungrooved surface of the flagellum are assumed to grip the inner wall of the spermathecal duct while penetrated by the flagellum during insemination or preinsemination clearing. The presence of tempers on one side of the flagellum promotes rapid, smooth insertion and removal of the flagellum from the duct. It is proposed that tempers of the flagellar groove assist the flow of seminal materials to the spermatheca by guiding the narrow neck of the spermatophore into the spermathecal duct while the flagellum is inserted.

The aphid genus Tinocallis Matsumura is revised on a worldwide basis. Notes on its taxonomic position and evolutionary history and a key for the 21 species are presented. Tinocallis ussuriensis Pashtshenko and T. nevskyi lianchengensis Zhang and Qiao are proposed as synonyms of T. takachihoensis, and T. sapporoensis Higuchi is proposed as a synonym of T. nikkoensis Higuchi, T. allozelkowae Zhang and Zhong as a synonym of T. viridis (Takahashi), and T. magnoliae AK Ghosh and Raychaudhuri as a synonym of T. insularis (Takahashi). Tinocallis distinctus MR Ghosh, AK Ghosh and Raychaudhuri is returned to the subgenus Tinocallis s.s. from the subgenus Quednaucallis Chakrabarti. A lectotype designation was made for T. viridis (Takahashi). Tinocallis dalbergicolasp.nov. from Dalbergia hancei Benth. (Fabaceae) in Hong Kong is described and illustrated. It is closely related to T. caryaefoliae (Davis) and T. himalayensis AK Ghosh, MR Ghosh and Raychaudhuri, but has much longer antennae and longer spinal body processes. It also differs from the former species by the smooth mesonotum and from the latter species in having the forewing hyaline and with a complete radial sector.

The wheat stem sawfly, Cephus cinctus Norton (Hymenoptera: Cephidae), has been the most economically important insect pest of wheat in the northern Great Plains since cultivation began (Weiss and Morrill 1992). The wheat stem sawfly was first reported from wild grasses where populations were often highly parasitized by a number of parasitoids, including Bracon (= Microbracon) cephi (Gahan) (Hymenoptera: Braconidae) (Criddle 1923; Ainslie 1929). A similar species, Bracon lissogaster Muesebeck, was later reported to also attack C. cinctus larvae (Muesebeck 1953; Somsen and Luginbill 1956). These parasitoids are now prevalent in wheat in some regions of Montana (Morrill et al. 1994, 1998; Morrill 1997). The life histories and phenologies of these sympatric idiobiont ectoparasitoids are similar. The ability to distinguish B. cephi from B. lissogaster is essential in elucidating their effects on populations of C. cinctus. We examined 159 females and 123 males of B. cephi from Chouteau, Hill, Stillwater, Teton, and Toole counties in Montana; Burke, Burleigh, Rolette, and Williams counties in North Dakota; Rock County in Minnesota; and southem Alberta (Rockyford and Consort). The 254 females and 215 males of B. lissogaster examined were from Chouteau, Hill, Teton, and Toole counties in Montana. Holotypes were compared to verify identifications.

We evaluated the resistance to tracheal mites, Acarapis woodi (Rennie) (Acari: Tarsonemidae), of colonies of honey bees, Apis mellifera L. (Hymenoptera: Apidae), headed by daughters of three queens from each of three honey bee stocks: (i) British Columbia "mite-resistant stock, (ii) Buckfast "mite-resistant" stock, and (iii) Canadian unselected stock. Colonies of all nine families were distributed among four apiaries; half of the colonies in each apiary were treated with formic acid to attempt to control tracheal mites. The study documented significant differences in resistance to tracheal mites among the families of bees, even within each of the three stocks. After the first 4 months of study (by November 1993), differences in mite infestations had developed among the nine families. Formic acid treatments had either short-lived effectiveness (1993) or no effect (1994) on tracheal mite infestations, thereby eliminating the opportunity to evaluate colony performance in the absence of mites. Mite infestations varied significantly among apiary sites. This study highlights the value of evaluating sets of colonies headed by sister queens when identifying mite-resistant stock for breeding purposes.