Cylindrocopturus Adspersus Research Articles

Reassessment of Resistance to Sunflower Stem Weevil, Cylindrocopturus adspersus LeConte (Coleoptera: Curculionidae), in Cultivated Sunflower Germplasm

Sunflower stem weevil, Cylindrocopturus adspersus LeConte (Coleoptera: Curculionidae), larval feeding on pith and vascular tissues can weaken stalks of cultivated sunflower, leading to breakage and loss of harvestable yield. Previous research has suggested host plant resistance (HPR) to this pest is possible, but results have been difficult to interpret because of limited comparisons to cultivated inbreds and hybrids, along with possible confounding effects of stem diameter. Trials in Kansas (2012) and Nebraska (2015) were used to help reassess the value of germplasm with putative resistance to sunflower stem weevil. Field tests in 2012 included 28 inbreds and hybrids and three entries previously identified as resistant. Though a putative resistance source, PI 386230, was infested with fewer weevil larvae per stem than several hybrids, differences primarily appeared to be due to stem diameter, which is strongly correlated with the number of weevil larvae per stem. A follow-up trial in 2015 suggested differences in larval infestation were not attributable to other qualities in groups of germplasm that differ in stem diameter (i.e., males, females or hybrids), but that changes in plant density predictably alter both stem diameter and numbers of stem weevil larvae. Though resistance to sunflower stem weevil and other stem-feeding pests may be possible, the cost and difficulty of developing HPR, declining severity of the pest, and availability of other simple management options are significant disincentives to additional research.

Temperature variability is a key component in accurately forecasting the effects of climate change on pest phenology

Models describing the effects of climate change on arthropod pest ecology are needed to help mitigate and adapt to forthcoming changes. Challenges arise because climate data are at resolutions that do not readily synchronize with arthropod biology. Here we explain how multiple sources of climate and weather data can be synthesized to quantify the effects of climate change on pest phenology. Predictions of phenological events differ substantially between models that incorporate scale-appropriate temperature variability and models that do not. As an illustrative example, we predicted adult emergence of a pest of sunflower, the sunflower stem weevil Cylindrocopturus adspersus (LeConte). Predictions of the timing of phenological events differed by an average of 11 days between models with different temperature variability inputs. Moreover, as temperature variability increases, developmental rates accelerate. Our work details a phenological modeling approach intended to help develop tools to plan for and mitigate the effects of climate change. Results show that selection of scale-appropriate temperature data is of more importance than selecting a climate change emission scenario. Predictions derived without appropriate temperature variability inputs will likely result in substantial phenological event miscalculations. Additionally, results suggest that increased temperature instability will lead to accelerated pest development. © 2016 Society of Chemical Industry.

Methods for assessing infestations of sunflower stem weevil (Coleoptera: Curculionidae) in sunflower stems

AbstractThe sunflower stem weevil, Cylindrocopturus adspersus LeConte (Coleoptera: Curculionidae), reduces sunflower, Helianthus annuus Linnaeus (Asteraceae), yields by spreading pathogens, damaging vascular tissues, and promoting lodging of sunflower plants. To assess weevil populations for host plant resistance and insecticide field trials, larvae are dissected out of stems and counted; a process that is slow and limits experimental designs. To improve efficiency of sunflower stem weevil sample processing, field-collected sunflower samples were used to evaluate whether digital radiographs (X-rays) of stem sections or population estimates from rearing out overwintering stem weevils are suitable substitutes for dissection of complete stems. Digital X-rays of small stem pieces (15 cm above soil level) split longitudinally were found to explain over 75% of the variation in numbers of weevil larvae from dissected stem samples (50 cm), but required less than one-fifth the time of manual dissection. Use of small emergence boxes to estimate weevil populations was similarly time efficient, but may not be easily related to weevils per plant because of parasitism and other mortality. Results suggest for large field trials with sunflower stem weevils, digital X-rays provide much more time-efficient larval population estimates.

Sunflower Stem Weevil and Its Larval Parasitoids in Native Sunflowers: Is Parasitoid Abundance and Diversity Greater in the U.S. Southwest?

Classical biological control programs often target a pest's region of origin as a likely source for new biological control agents. Here, we use this approach to search for biological control agents of the sunflower stem weevil (Cylindrocopturus adspersus LeConte), an economically important pest of commercial sunflower. We conducted surveys of weevil natural enemy diversity and abundance across a transect running from the northern Great Plains to the southwestern U.S. (the presumed area of endemism of annual sunflower species in the genus Helianthus). Accordingly, natural enemy diversity and abundance were expected to be greater in the southwestern U.S. C. adspersus and their larval parasitoids were collected from stems of four native sunflower species (Helianthus annuus, H. nuttallii, H. pauciflorus, and H. petiolaris) from 147 sites across eight states. Native H. annuus constituted the majority of the sunflower populations. Mean weevil densities were significantly higher in sunflower stalks that were larger in diameter. Mean weevil densities within sites did not differ across the range of longitudes and latitudes sampled. After accounting for the effects of stalk diameter and location, weevil densities did not differ among the four sunflower species nor did they differ as a function of elevation. C. adspersus in H. annuus and H. petiolaris were attacked by seven species of parasitoids. No parasitoids were found attacking C. adspersus in H. nuttallii or H. pauciflorus stalks. C. adspersus were twice as likely to be attacked by a parasitoid when feeding on H. petiolaris than H. annuus. Furthermore, the likelihood that C. adspersus would be parasitized decreased with increasing elevation and increasing stem diameters. All parasitoid species have been previously reported attacking C. adspersus larvae in cultivated sunflower. Species richness was less diverse in these collections than from previous studies of cultivated sunflower. Our findings suggest that the species of larval parasitoids attacking C. adspersus in native sunflowers have successfully made the transition to cultivated sunflower.

Nonlinear Degree-Day Models for Postdiapause Development of the Sunflower Stem Weevil (Coleoptera: Curculionidae)

The sunflower stem weevil, Cylindrocopturus adspersus (LeConte) (Coleoptera: Curculionidae), has caused yield losses across much of the western Great Plains. Little is known about the field biology of this pest. Simple prediction models, such as degree-day models, are an integral tool for development of C. adspersus management strategies. Using data collected in Colorado, Kansas, and Nebraska, we sought for predictable variation between C. adspersus pupation, adult eclosion, and emergence and accumulated degree-days Celsius (DD) by using a temperature threshold of 5 degrees C. Accurate phenological models can be used to time scouting efforts and pesticide applications. The relationship between phenological data and accumulated DD fit nonlinear, Gaussian distributions better than uniform distributions. Phenological models were developed to describe these distributions for pupation, adult presence within the stalk and adult emergence. The pupation model predicts 50% pupation at 197 DD and 90% at 307 DD. Model results predict that 50% of adult eclosion within the stalks will have transpired at 396 DD and 90% at 529 DD. A model-averaged result from two data sets predicts 5% adult emergence from stalks at 262 DD, 50% emergence at 540 DD, 75% emergence at 657 DD, and 90% at 777 DD. Scouting for adults thus can be initiated at 262 DD. Current chemical controls target adults to prevent oviposition. Thus, applications therefore should not be made before this point.

Resistance Among Cultivated Sunflower Germplasm to Stem-Infesting Pests in the Central Great Plains

A 7-yr field study evaluated 61 oilseed sunflower, Helianthus annuus L., accessions and 31 interspecific crosses for resistance to attack by naturally occurring populations of three stem-infesting pests, the sunflower stem weevil, Cylindrocopturus adspersus (LeConte) (Coleoptera: Curculionidae); a longhorned beetle, Dectes texanus LeConte (Coleoptera: Cerambycidae); and a root boring moth, Pelochrista womonana (Kearfott) (Lepidoptera: Tortricidae), at two locations in the central Great Plains. Germplasm with potential sources of resistance to attack from all three stem-infesting species were revealed. Accessions PI 650558, PI 386230, and PI 431516 were consistent in averaging low densities of stem weevil larvae per stalk among lines tested, and PI 497939 exceeded 25 weevil larvae per stalk in only 1 yr of 5 yr of trials. Several interspecific crosses also had consistently low densities of C. adspersus larvae per stalk. Populations of both D. texanus and P. womonana were variable over years, but differences among the lines tested were evident in many trials, revealing potential for developing resistant germplasm. Four accessions (PI 386230, PI 431542, PI 650497, and PI 650558) had low larval densities of C. adspersus and P. womonana in addition to reduced percentage infestation by D. texanus. Results showed potential for developing resistant genotypes for these pests. The prospect of adding host plant resistance as an integrated pest management (IPM) tactic would provide another tool for reducing economic losses from stem-infesting insect pests of sunflower in the central Great Plains.

Plant Spacing and Weed Control Affect Sunflower Stalk Insects and the Girdling Behavior of <I>Dectes texanus</I> (Coleoptera: Cerambycidae)

We conducted a 2-yr study to determine the effects of crop density and weeds on levels of damage caused by stalk-boring insects in rain-fed sunflowers in west-central Kansas. Weed-free sunflower had higher seed weight and oil content in 2007, but not in 2006, but weeds did not affect infestation by stalk-boring insects in either year. High-density sunflower had lower estimated seed yield per unit area than low-density sunflower in both years, but percentage oil was slightly greater in the high-density treatment in 2006. Sunflowers were more heavily infested by larvae of Ataxia hubbardi Fisher, Cylindrocopturus adspersus (Leconte), and Pelochrista womanana (Kearfott) in 2006 than in 2007, ostensibly as a result of being planted earlier. Larvae of Dectes texanus LeConte appeared unaffected by planting date and were present in > 70% of plants in both years. Conditions during the period of crop maturity were much drier in 2006 than in 2007 and were associated with higher seed oil content and earlier and faster progression of stalk girdling by D. texanus larvae in both low- and high-density plots. There was also a strong effect of plant density on girdling behavior that seemed to be mediated by effects on soil moisture. Stalk girdling began earlier in high-density plots and a larger proportion of plants were girdled compared with low-density plots on all sampling dates in both years. Certain cultural tactics, in particular reduced plant spacing, have potential to delay the onset of girdling behavior by D. texanus larvae and thus mitigate losses that otherwise result from the lodging of girdled plants.

Impact of Irrigation on Larval Density of Stem-Infesting Pests of Cultivated Sunflower in Kansas

The guild of stem-infesting insect pests of cultivated sunflower, Helianthus annuus L., within the central Plains is a concern to producers, chiefly due to losses caused by plant lodging from the sunflower stem weevil, Cylindrocopturus adspersus (LeConte) (Coleoptera: Curculionidae), and Dectes texanus texanus LeConte (Coleoptera: Cerambycidae). The incidence of a root boring moth, Pelochrista womonana (Kearfott) (Lepidoptera: Tortricidae), also has increased. Experiments were conducted in Kansas during 2000-2001 to investigate the effect of irrigation timing and intensity on densities of C. adspersus, D. texanus, and P. womonana larvae within cultivated sunflower stalks. Supplemental soil moisture provided by irrigation during the growing season increased both seed yield and oil content, and it reduced insect densities of the sunflower stem weevil and P. womonana in the sunflower stalk. Results showed that ensuring adequate moisture during the growing season can assist in reducing stem-infesting insect densities, revealing an additional advantage of crop irrigation beyond improved sunflower productivity.

Plant population and weeds influence stalk insects, soil moisture, and yield in rainfed sunflowers

AbstractInsect infestation, soil moisture, and yield were examined in populations of ≈ 33 140 plants/ha (low) and ≈ 40 340 plants/ha (high) of an oilseed sunflower, Helianthus annuus L, cv.‘Triumph 660CL’with two levels of weediness. Less weedy plots resulted from the application of herbicide combination of S‐metolachlor and sulfentrazone, whereas more weedy plots resulted from application of sulfentrazone alone. Among the 12 weed species recorded, neither plant numbers nor biomass differed between crop plant densities. Larvae of the stalk‐boring insects Cylindrocopturus adspersus (Coleoptera: Curculionidae) and Mordellistena sp. (Coleoptera: Mordellidae) were less abundant in high density sunflowers, ostensibly due to reduced plant size. However, the same effect was not observed for Dectes texanus (Coleoptera: Cerambycidae) or Pelochrista womanana (Lepidoptera: Tortricidae), two other stalk‐boring insects. Soil moisture was highest in low density and lowest in the high density sunflowers that were less weedy. Stalk circumference, head diameter, and seed weight were reduced for sunflower plants with short interplant distances (mean = 20 cm apart) compared to plants with long interplant distances (mean = 46 cm apart). These three variables were greater in less weedy plots compared with more weedy plots and positively correlated with interplant distance. Yields on a per‐hectare basis paralleled those on a per‐plant basis but were not different among treatments. The agronomic implications of planting density are discussed in the context of weed and insect management.

Impact of Combining Planting Date and Chemical Control to Reduce Larval Densities of Stem-Infesting Pests of Sunflower in the Central Plains

The guild of stem-infesting insect pests of sunflower, Helianthus annuus L., within the central Plains is a concern to producers chiefly due to losses caused by plant lodging from the sunflower stem weevil, Cylindrocopturus adspersus (LeConte) (Coleoptera: Curculionidae), and Dectes texanus texanus LeConte (Coleoptera: Cerambycidae). The incidence of a root boring moth, Pelochrista womonana (Kearfott) (Lepidoptera: Tortricidae), also has increased. Experiments were conducted in three locations in Colorado and Kansas during 2001–2003 to investigate the potential of combining planting date and foliar and seed treatment insecticide applications to lower insect stalk densities of these three pests. The impact of these strategies on weevil larval parasitoids also was studied. Eight sunflower stem weevil larval parasitoid species were identified. All were Hymenoptera and included the following (relative composition in parentheses): Nealiolus curculionis (Fitch) (42.6%), Nealiolus collaris (Brues) (3.2%) (Braconidae), Quadrastichus ainsliei Gahan (4.2%) (Eulophidae), Eurytoma tylodermatis Ashmead (13.1%) (Eurytomidae), Neocatolaccus tylodermae (Ashmead) (33.7%), Chlorocytus sp. (1.6%), Pteromalus sp. (0.5%) (Pteromalidae), and Eupelmus sp. (1.0%) (Eupelmidae). The results from this 3-yr study revealed that chemical control was often reliable in protecting the sunflower crop from stem pests and was relatively insensitive to application timing. Although results in some cases were mixed, overall, delayed planting can be a reliable and effective management tool for growers in the central Plains to use in reducing stem-infesting pest densities in sunflower stalks. Chemical control and planting date were compatible with natural mortality contributed by C. adspersus larval parasitoids.

Impact of Combining Planting Date and Chemical Control to Reduce Larval Densities of Stem-Infesting Pests of Sunflower in the Central Plains

The guild of stem-infesting insect pests of sunflower, Helianthus annuus L., within the central Plains is a concern to producers chiefly due to losses caused by plant lodging from the sunflower stem weevil, Cylindrocopturus adspersus (LeConte) (Coleoptera: Curculionidae), and Dectes texanus texanus LeConte (Coleoptera: Cerambycidae). The incidence of a root boring moth, Pelochrista womonana (Kearfott) (Lepidoptera: Tortricidae), also has increased. Experiments were conducted in three locations in Colorado and Kansas during 2001-2003 to investigate the potential of combining planting date and foliar and seed treatment insecticide applications to lower insect stalk densities of these three pests. The impact of these strategies on weevil larval parasitoids also was studied. Eight sunflower stem weevil larval parasitoid species were identified. All were Hymenoptera and included the following (relative composition in parentheses): Nealiolus curculionis (Fitch) (42.6%), Nealiolus collaris (Brues) (3.2%) (Braconidae), Quadrastichus ainsliei Gahan (4.2%) (Eulophidae), Eurytoma tylodermatis Ashmead (13.1%) (Eurytomidae), Neocatolaccus tylodermae (Ashmead) (33.7%), Chlorocytus sp. (1.6%), Pteromalus sp. (0.5%) (Pteromalidae), and Eupelmus sp. (1.0%) (Eupelmidae). The results from this 3-yr study revealed that chemical control was often reliable in protecting the sunflower crop from stem pests and was relatively insensitive to application timing. Although results in some cases were mixed, overall, delayed planting can be a reliable and effective management tool for growers in the central Plains to use in reducing stem-infesting pest densities in sunflower stalks. Chemical control and planting date were compatible with natural mortality contributed by C. adspersus larval parasitoids.

Impact of the Stem Borer,Dectes texanus, on Yield of the Cultivated Sunflower,Helianthus annuus.

Foliar and soil-drench insecticide treatments were used in attempts to manipulate infestation of cultivated sunflower plants, Helianthus annuus LeConte (Asterales: Asteraceae) by Dectes texanus LeConte, (Coleoptera: Cerambycidae) a serious pest of sunflowers in the High Plains of the USA. Seed yields were assessed on a per-plant basis for both oilseed and confection type sunflower hybrids in two years. Both insecticide treatments (foliar ë-cyhalothrin and soil-drench carbofuran) improved yield of oilseed sunflowers in 2004, but not in 2005. Yield of confection hybrids was improved by a systemic fungicide (thiophanate methyl) in 2005, but insecticides did not improve yield in either year. Both insecticide treatments gave good control of various stalk-boring insects such as Cylindrocopturus adspersus (Coleoptera: Curculionidae), Mordellistena sp. (Coleoptera: Mordellidae), and Pelochrista womanana (Lepidoptera: Tortricidae), but neither gave better than 50% control of D. texanus. Plants were sorted according to the presence or absence of D. texanus larvae and no reduction was found in total seed weight, seed size, or oil content as a result of infestation. However, mature larvae of D. texanus girdle stalks at the base in preparation for overwintering, a behavior that reduced stalk breakage force by 34–40%, leading to yield losses through lodging. At harvest in 2005, there were differences between cultivars and among treatments in the proportions of D. texanus larvae that had girdled their plants at harvest. It was concluded that further research aimed at reducing crop losses to D. texanus should focus on means of delaying stalk desiccation and/or deterioration, factors that appear to trigger girdling behavior.

Influence of Planting Date on Sunflower Stem Weevil (Coleoptera: Curculionidae) Larval Density and Parasitism in Oilseed and Confection Sunflower in Western Kansas

The sunflower stem weevil infests stalks of cultivated sunflower and can cause lodging resulting in loss of the head prior to harvest. Our objective was to determine whether altered planting periods could reduce weevil densities in confection and oilseed sunflower in the central High Plains production region. We evaluated impact of planting date by measuring larval density within sunflower stalks, larval parasitoid species present, and parasitization rates. Trials were conducted at Colby, KS from 1999 to 2001, with plots seeded in four planting periods. Results, although inconsistent over years and between the two sunflower types, showed that later planting dates reduced weevil density in stalks. Weevil numbers in stalks from the first seeding period until the last had decreased by 10% to 50%. The third planting date in each year coincided with cumulative degree-days (581) for the predicted emergence of 90% of adult sunflower stem weevils. Yields were not reduced as planting was delayed. Fewer weevils were observed in oilseed than in confection hybrids. Lower densities of sunflower stem weevils in the stalk can reduce losses from lodged plants. Seven hymenopteran parasitoid species were reared from sunflower stem weevil larvae. Nealiolus curculionis (Fitch) and Neocatolaccus tylodermae (Ashmead) were the most common species. Parasitization rates were low, but wasps actively attacked the weevil throughout the growing season. Research showed that delaying planting until after the early and later May planting periods reduced weevil densities in western Kansas.

First Report of Charcoal Rot (Macrophomina phaseolina) on Sunflower in North and South Dakota.

In September 1998, symptoms suggestive of charcoal rot were observed on oilseed sunflower (Helianthus annuus L.) plants in western North and South Dakota. Symptoms first observed on plants approaching physiological maturity consisted of silver-gray lesions girdling the stem at the soil line, premature plant death, and reduced head diameter. The pith in the lower stem was completely absent or compressed into horizontal layers. Black, spherical microsclerotia were observed in the pith of the lower stem, underneath the epidermis, and on the exterior of the taproot. Confirmation of Macrophomina phaseolina (Tossi) Goid. as the causal agent was based on the size of the microsclerotia, which ranged from 80 to 90 μm in diameter, from both infected sunflowers and pure cultures (1). The only other sunflower pathogen known to form microsclerotia is Verticillium dahliae Kleb., whose microsclerotia are irregular in shape and are 15 to 50 μm in diameter. Some prematurely dead sunflower plants lacked typical charcoal rot stem lesions, but contained Macrophomina microsclerotia. Plants with atypical symptoms were colonized by the sunflower stem weevil (Cylindrocopturus adspersus (LeConte)) and the black sunflower stem weevil (Apion occidentale Fall). This agrees with observations in Texas, where Macrophomina-infected sunflower plants parasitized by stem-feeding insects often displayed atypical charcoal rot symptoms (3). Charcoal rot incidence in 1998 in western North Dakota was 25%, compared with 0% in eastern North Dakota. Charcoal rot was not observed in 1999, the fourth wettest growing season on record, but was observed again in 2000 and 2001. The recent increase in sunflower production in western North and South Dakota, areas typically hotter and drier than the eastern portions of both states, and the potential involvement of stem weevils as vectors of Macrophomina (2) may lead to an increased incidence of charcoal rot in sunflower.

Sunflower stem weevil and its larval parasitoids in the Central and Northern Plains of the USA

The sunflower stem weevil, Cylindrocopturus adspersus (LeConte) (Coleoptera:Curculionidae), is apest of cultivated sunflower (Helianthusannuus L) from the southern to the northernGreat Plains. The incidence of weevilinfestation in fields from the six differentstates sampled during 1996 and 1997 ranged from33% (Minnesota) to 100% (Kansas, Colorado,Nebraska). Weevil populations in the fieldssampled were statistically greater in thecentral Plains (Colorado, Kansas, Nebraska)with a mean of 12.3 and 19.5 larvae per stalkcompared with the northern Plains (North andSouth Dakota, Minnesota) of 0.7 and 1.3 larvaeper stalk in 1996 and 1997, respectively.Parasitization of weevils varied from field tofield ranging from 1 to 100%, but was usuallyless than 20%. The nine species oflarval parasitoids recovered were allHymenoptera and included: Nealioluscurculionis (Fitch), N. collaris(Brues), Bracon sp. (Braconidae); Neocatolaccus tylodermae (Ashmead), Chlorocytus sp., Pteromalus sp.(Pteromalidae); Quadrastichus ainslieiGahan (Eulophidae), Eurytoma tylodermatisAshmead (Eurytomidae); and Eupelmus sp.(Eupelmidae). Nealiolus curculionis wasthe most prevalent parasitoid reared from C. adspersus, and it was recovered from allstates sampled. Parasitoid species richness wasgreatest in the central Plains. Thereduced number of parasitoid species foundattacking C. adspersus in the northernPlains may be caused by low host populationlevels, slow migration by parasitoids into theregion, or lack of adaptation to climaticconditions. Additional work to understandthe population dynamics of the parasitoidcomplex associated with C. adspersus mayresult in improved biological control of thesunflower stem weevil in cultivatedsunflower.

Very long-chain methyl-branched alcohols and their acetate esters in pupal internal lipids of developing Coleoptera, Anthonomus grandis and Cylindrocopturus adspersus, and Diptera, Cochliomyia hominivorax and Musca domestica

Mono- and dimethyl-branched primary alcohols from C28 to C56 were identified in the internal lipids of developing mid-stage pupae of two species of Coleoptera; the boll weevil, Anthonomus grandis and the sunflower stem weevil, Cylindrocopturus adspersus, and of two species of Diptera; the screwworm, Cochliomyia hominivorax, and the house fly, Musca domestica. Novel very long-chain dimethyl-branched alcohols (VLMA; C36–C56) were characterized for the first time in these two orders. The major VLMA component was 26,38-dimethylpentacontanol in the boll weevil, 28,38-dimethylpentacontanol in the sunflower stem weevil, and 26,36-dimethyloctatetracontanol in both the screwworm and house fly. These alcohols were six to ten carbons longer than similar alcohols previously reported for Lepidoptera. No terminally-branched or trimethyl-branched alcohols similar to those previously characterized in Lepidoptera were detected.

Evaluation of Planting Treatments for Sunflower Stem Weevil Control, 1997

Abstract Sunflower test plots were planted 14 May at the Central Great Plains Research farm 4 miles east of Akron, CO. Plots were 4 rows wide (22-inch row spacing) by 50 ft long and arranged in a RCB with four replications. The two row planter was calibrated to plant 18,000 seeds/acre. The soil type was a Weld silt loam. Gaucho 480°F seed treatment was applied at three rates; (8.2, 12.3, and 16.4 oz (AI)/cwt seed). Furadan 4°F was injected in the seed furrow at planting immediately following seed placement and prior to planter press wheels in a 1:1 (water:Furadan 4 F) dilution using a microinjection unit. Evaluations for lodged plants were made on 27 Sep by counting all plants in the center 2 rows followed by counting the number lodged. Mature SSW larvae were counted by dissecting four stalks from each plot on 15 Oct. Only the lower 18 inches of stalk was dissected. The diam of each stalk was measured at the cotyledon scars. The center two rows of each plot were hand harvested and thrashed. Yield data are adjusted to 10% moisture.

Biochemistry and physiology of overwintering in the mature larva of the sunflower stem weevil, Cylindrocopturus adspersus (Coleoptera: Curculionidae) in the Northern Great Plains

The sunflower stem weevil, Cylindrocopturus adspersus (LeConte), overwinters as a mature larva at the base of the stalk and in the root crown of cultivated sunflower plants. Sunflower stalks from fields known to be infested with C. adspersus larvae were collected in southeastern North Dakota in October 1991. Larvae from stalks kept outdoors accumulated a high whole-body concentration of trehalose (up to 69 μg/mg wet wt) at the expense of glycogen with the onset of winter followed by a partial reconversion of trehalose to glycogen with the onset of spring. Larvae from stalks acclimated to 0°C also accumulated a high level of trehalose (∼69 μg/mg wet wt) with a concomitant decrease in glycogen. Those larvae from stalks kept at 20°C showed an initial sharp increase in whole-body trehalose that then stabilized but at a concentration well below that of larvae acclimated to 0°C. This indicates that there exists in the larva an underlying developmental component to trehalose accumulation which is further enhanced by low temperature (0°C) exposure. The mean temperature of crystallization ( T c) of larvae exposed to outdoor conditions showed an abrupt drop from October (−25.0 ± 1.3°C) to November (−28.2 ± 0.6°C) with a minimum in February (−29.1 ± 0.3°C). The level of trehalose accumulated by the sunflower stem weevil larva is to our knowledge the highest reported in an overwintering insect.

Seasonal Abundance and Impact of the Sunflower Stem Weevil Parasitoid, Nealiolus curculionis (Hymenoptera: Braconidae), in the Northern Great-Plains1

Abstract Nealiolus curculionis (Fitch) is a univoltine, solitary, endophagous larval parasitoid of the sunflower stem weevil, Cylindrocopturus adspersus (LeConte), in both cultivated and native sunflower. This parasitoid represented 96% of all parasitoids attacking the weevil from 1980 to 1991. Adult parasitoids were active in the field from late June to late August (1980-1985). Eggs were deposited in early instar weevils feeding within the sunflower stem. The immature parasitoids overwintered in diapausing weevil larvae in the sunflower stem. Parasitization of overwintering sunflower stem weevil larvae varied from 5 to 32% (1980 to 1991). Adult parasitoids emerged in early June through mid-July, which was earlier and more rapid than the emergence of their host. Postdiapause development of N. curculionis required 31 days after the parasitoid larvae exited the weevil larva for adult eclosion. Parasitoid males and females lived 9 days in the laboratory when supplied with honey as a food source. Results indicated that overall parasitization has increased from levels reported in the late 1970s and early 1980s. The parasitoid appears to be a consistent mortality factor in the population dynamics of the sunflower stem weevil in cultivated sunflower, though the adult populations are often low.

Comparison of glycosylated and deglycosylated vitellins from four species of weevil (Coleoptera: Curculionidae)

1. 1. The vitellins or yolk proteins of four species of weevil (Coleoptera: Curculionidae) consist of two size classes with molecular weights of 150–170 and 42–47 kilo daltons (kDa). 2. 2. The boll weevil, Anthonomus grandis, has one large vitellin while Smicronyx fulvus, S. sordidus, and Cylindrocopturus adspersus each have two large vitellins. 3. 3. All four weevils have a single small vitellin whose size differs with genera. 4. 4. In all four species both large and small vitellins contain N-linked glycosyl groups. 5. 5. Enzymatic removal of the N-linked glycosyl chains lowers the molecular weight of the vitellins 9–17%.