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The wheat stem sawfly, Cephus cinctus Norton (Hymenoptera: Cephidae), is historically one of the most important economic insect pests in the northern Great Plains of North America. Within this geographical region, the areas subjected to greatest attack are southern Alberta and Saskatchewan, southwestern Manitoba, eastern and northern Montana, North Dakota, northern South Dakota, and western Minnesota. Cumulative grain-yield losses and annual economic losses associated with this pest can exceed 30% and $350 million, respectively. Solid-stemmed cultivars of common wheat, Triticum aestivum L. (Poaceae), tolerant of infestation, are critical for C. cinctus management, but outbreaks of this pest continue to occur even after six decades of cultivar development. Furthermore, chemical control (a primary control option for other cereal (Poaceae) insect pests) has proven ineffective; this underscores the need to integrate resistant cultivars into a comprehensive integrated pest management program. We provide overviews of wheat stem sawfly biology, recent advances in applied research, the efficacy and integration of cultural and biological management strategies, and future directions for global research activities to manage wheat stem sawfly.
Scanning electron microscopy on the ultrastructure of scales on the forewings and labial palpi suggests species-diagnostic differences among six sibling species of the genus Ostrinia Hübner. Among four species with small mid-tibiae, O. furnacalis (Guenée) and O. nubilalis (Hübner) show similar ultrastructure of the distal forewing scales, which is distinctly different from that of O. orientalis Mutuura and Munroe and O. dorsivittata (Moore). The diameter of windows between longitudinal ridges and cross ribs of forewing scales in O. dorsivittata is the largest among examined species, and clearly different from that in the other three small midtibiae species. Scales of the labial palpi of O. orientalis have indistinct vestigial windows; windows of O. nubilalis are more numerous and larger than in the other three small mid-tibiae species. Among two species with massive mid-tibiae, window diameter of forewing scales is larger in O. zealis (Guenée) than in O. scapulalis (Walker). Moreover, the number and diameter of windows in scales of the labial palpi differs between these two species. In addition to other known morphological differences, these ultrastructural differences provide further evidence that closely related Ostrinia species are distinct.
Systematics & Morphology / Systématique et morphologie
Hodostates Foerster is revised, representing the first comprehensive comparison of Nearctic and European species. Three species are recognized as valid, and the Nearctic Hodostates rotundatus (Davis) is recorded from Canada for the first time. Hodostates schaffneri Hinz is transferred to Lethades Davis, based largely on ovipositor morphology, and is redescribed. Placement in the tribe Pionini is discussed, given the presence of a deep subapical notch in the ovipositor of both New and Old World species of Hodostates. Host records for Hodostates are reviewed.
Physiology, Biochemistry, Development & Genetics / Physiologie, biochimie, dé veloppement et génétique
Six subspecies of Bacillus thuringiensis Berliner (Bt) were grown in minimal medium with chitin as the sole carbon source for 6 days to obtain Bt cell-free fermented broths, which were then evaluated for chitinolytic activity and tested against third-instar Aedes aegypti (L.) (Diptera: Culicidae) larvae. Bt Pakistani showed the highest chitinolytic activity (approximately >2700 mU/mL), Bt kurstaki showed the lowest activity (approximately <2000 mU/mL), and Bt thompsoni, Bt aizawai, Bt israelensis, and Bt alesti showed intermediate activities (approximately 2100–2400 mU/mL). Bt aizawai and Bt thompsoni broths showed the highest toxicity (LC50) against third-instar A. aegypti larvae (approximately <290 mU/mL). Bt kurstaki broth showed the lowest toxicity (approximately 420 mU/mL), while Bt pakistani, Bt israelensis, and Bt alesti broths showed intermediate toxicities (approximately 360–460 mU/mL). A purified and biochemically characterized Bt aizawai chitinase and commercial chitinases (from Serratia marcescens Bizio and Streptomyces griseus Waksman and Henrici) were evaluated and compared for synergistic effects on Bt israelensis spore-toxin complex against third-instar A. aegypti larvae. The synergism factor value of Streptomyces griseus and Bt aizawai chitinases were >2 and approximately 1.4; synergism was not evident for the Serratia marcescens chitinase (synergism factor value approximately 0.9).
The host range of a mixture of Choristoneura fumiferana (Clemens) nucleopolyhedroviruses (CfMNPV and CfDefNPV) was investigated using a per os bioassay of larvae of 29 species of Lepidoptera and adult males of Megachile rotundata (F.) (Hymenoptera: Megachilidae). Using a whole-genomic DNA probe, positive results were obtained in 8 of 10 Tortricidae: Archips cerasivorana (Fitch), Choristoneura fractivittana (Clemens), C. fumiferana, Choristoneura occidentalis Freeman, Choristoneura pinus pinus Freeman, Choristoneura rosaceana (Harris), Clepsispersicana (Fitch), and Cydia pomonella (L.); one Crambidae: Ostrinia nubilalis (Hübner); one arctiine Erebidae: Estigmene acrea (Drury); and two Noctuidae: Oligia illocata (Walker) and Pyrrhia exprimens (Walker). Mortality rates were highest among C. fumiferana, C occidentalis, C. pinus pinus, A. cerasivorana, and C. pomonella. Sequenced polymerase chain reaction (PCR) amplicons from infected individuals from several species confirmed that the primer sets amplified the target viruses. CfMNPV was consistently found in virus-fed C. fumiferana; whereas, CfDefNPV was present only occasionally. The presence of CfMNPV and CfDefNPV in A. cerasivorana was confirmed by PCR and DNA sequencing. Significant treatment-mortality rates were induced in the noctuids P. exprimens and Acronicta impleta Walker; PCR determined that both viruses were present in treated P. exprimens but only CfMNPV was present in A. impleta. No virus was detected in M. rotundata.
The effects of sublethal doses (LD10: 1.00 ng/larva; LD30: 3.75 ng/larva) of chlorfluazuron on the biochemical constituents of eggs of the tobacco cutworm, Spodoptera litura (F.), are described. Chlorfluazuron was applied topically to fifth-instar larvae and the subsequent adults were allowed to mate according to larval treatment (LD10-treated female × LD10-treated male and LD30-treated female × LD30-treated male). Biochemical constituents of eggs resulting from these pairings were analyzed at various stages of embryonic development. Compared with controls, LD10 or LD30 reduced egg constituents as follows: protein (min.—max.) by 32.8%–34.5% or 62.0%–67.3%, lipid by 33%–34% or 62%–67%, carbohydrates by 30%–39% or 60%–67%, DNA by 33%–40% or 60%–69%, RNA by 31%–34% or 59%–67%, and ecdysteroid by 22%–83% or 28%–92%, respectively. The relative proportions of constituents in control eggs were as follows: protein > lipid > carbohydrate, and RNA > DNA. Three low and three high peaks in ecdysteroid titres were observed. Compared with controls, all peaks were reduced in LD10 or LD30 eggs as follows: low peaks: 1st (at 8 h): 32% or 66%; 2nd (at 16 h): 33% or 67%; 3rd (at 52 h): 35% or 65%; high peaks: 1st (at 32 h): 83% or 92%; 2nd (at 64 h): 65% or 82%; 3rd (at 84 h): 84 h, 36% or 63%, respectively. In addition, the first two high peaks were delayed by 4 h in LD10 eggs and by 8 h in LD30 eggs compared with controls. Sublethal doses of chlorfluazuron reduced the amounts of biochemical constituents of eggs during embryogenesis in S. litura.
Biodiversity & Evolution / Biodiversité et evolution
Acrolepiopsis assectella (Zeller), leek moth, is a widespread and common pest of species of Allium L. (Liliaceae) in the western Palaearctic subregion. The establishment of A. assectella in eastern North America has resulted in economic losses to garlic (Allium sativum L.), leek (Allium porrum L.), and onion (Allium cepa L.) growers, especially to organic producers in eastern Ontario and southern Quebec. Acrolepiopsis assectella was first recorded in the Ottawa area in 1993. By 2010, A. assectella had expanded its range into eastern Ontario, southwestern Quebec, Prince Edward Island, and New York. A bioclimate model, using CLIMEX simulation software, was developed to produce mapped results that closely approximated known distributions for A. assectella in central Europe. This model was then validated with recorded distribution records in eastern Europe, Asia, and North America. Model output predicted that A. assectella will readily survive in southeastern Canada and the eastern United States of America. Other areas potentially suitable for A. assectella include coastal regions of the Pacific Northwest, the interior of southern British Columbia, and north-central Mexico. The continued range expansion of A. assectella into other Allium-growing areas of eastern North America appears to be inevitable. Establishment in these areas presents the risk of substantial production losses to Allium spp. producers.
The ceutorhynchine weevils Hadroplontus litura (F.) and Microplontus edentulus (Schultze) (Coleoptera: Curculionidae), are established in North America as biological control agents for Canada thistle, Cirsium arvense (L.) Scop., and scentless chamomile, Tripleurospermum perforatum (Mérat) M. Lainz (Asteraceae), respectively. In North America, both weeds occur sympatrically and in similar habitats as another ceutorhynchine, Ceutorhynchus obstrictus (Marsham) (cabbage seedpod weevil), an important pest of canola, Brassica napus L., and Brassica rapa L. (Brassicaceae). Ceutorhynchinae weevils released to control weeds in cultivated crops may serve as alternate hosts if agents released for biological control of C. obstrictus are not specific to that species. Parasitoids associated with M. edentulus and H. litura inflict similar levels of mortality on their hosts, yet a single species was associated with the latter host, whereas 13 species attacked the former. The stem-mining M. edentulus appears to be at some risk but not the root-crown feeding H. litura, should the parasitoids Trichomalus perfectus (Walker) and Mesopolobus morys (Walker) (Hymenoptera: Pteromalidae) be introduced as biological control agents of the silique-feeding C. obstrictus. These findings suggest that feeding niche may be an important criterion for developing a nontarget species test list for host-range testing of potential biological control agents.