Influence of soil temperature, rainfall, and planting and harvest dates on Chaetocnema confinis (Coleoptera: Chrysomelidae) damage to sweetpotato roots

A study was carried out in 10 counties of North Carolina from 2004 to 2006 to determine the effect of planting and harvest times on flea beetle, Chaetocnema confinis Crotch (Coleoptera: Chrysomelidae), damage to sweetpotato, Ipomoea batatas (L.), storage roots. Planting and harvesting of sweetpotatoes later in the season resulted in less damage than early planting and harvesting. Regression analysis was done to study the relationship of weather parameters with the flea beetle damage. Weather parameters included air temperature (Celsius), soil temperature at 5- and 10-cm depth (Celsius), rainfall (millimeters), and soil moisture (volume:volume) at 0-10-, 10-40-, and 40-100-cm depth. The best regression model included mean soil temperature at 10-cm depth, total rainfall, and number of adults caught on yellow sticky traps as independent variables (all between 1 August and harvest date of each field). Soil temperature and adult catches on yellow sticky traps of C. confinis were positively related to damage, whereas rainfall was negatively correlated. The model explained 45% of the total variation in the flea beetle damage. Soil temperature alone accounted for 32% of the total variation in flea beetle damage followed by rainfall (9%) and adult catches (4%). When the time interval was limited to 30 d before harvest, soil temperature was still the best explanatory variable accounting for 23% of the total variation in flea beetle damage followed by rainfall (7%) and adult catches (4%). Understanding the effects of planting/harvesting and weather factors on flea beetle damage will be useful in predicting the time when the sweetpotato crop is at greater risk from high levels of damage by C. confinis.     

Improved dry-fleshed sweetpotato genotypes resistant to insect pests

Thirty-five mostly dry-fleshed sweetpotato, Ipomoea batatas (L.) Lam. (Convolvulaceae), genotypes from the USDA-ARS/Clemson University sweetpotato breeding program were evaluated in nine field experiments at the U.S. Vegetable Laboratory, Charleston, SC, from 1998 to 2004. There were highly significant entry effects for percentage of uninjured roots; wireworm, Diabrotica, and Systena (WDS) index; percentage of roots damaged by sweetpotato weevil, Cylas formicarius elegantulus (Summers); percentage of roots damaged by sweetpotato flea beetle, Chaetocnema confinis Crotch); and percentage of roots damaged by white grub larvae (primarily Plectris aliena Chapin). The susceptible control, 'SC1149-19', had a significantly lower percentage of uninjured roots, a significantly higher WDS rating, and higher percentage infestations of flea beetle, grubs, and sweetpotato weevils than all other sweetpotato entries in this study. Twenty-seven genotypes had significantly less insect damage than 'Beauregard', the leading commercial orange-fleshed cultivar in the United States. In addition, 11 genotypes had significantly less insect injury than 'Picadito', a commercial boniato-type sweetpotato grown extensively in southern Florida. Overall, no genotypes were more resistant to soil insect pests than the resistant checks 'Sumor' and 'Regal'. Many of the advanced dry-flesh sweetpotato genotypes had high levels of resistance to soil insect pests, and they represent a useful source of advanced germplasm for use in sweetpotato breeding programs.     

Insect resistance in sweetpotato plant introduction accessions

Fifty-five sweetpotato cultivars, experimental breeding clones, and plant introduction (PI) accessions were evaluated in 17 field experiments at the USDA, ARS, U.S. Vegetable Laboratory (Charleston, SC; 12 evaluations, 1997-2010), the Clemson University, Edisto Research and Education Center (Blackville, SC; two evaluations, 1998-1999), and the University of Florida, Tropical Research and Education Center (Homestead, FL; three evaluations, 2005-2007). These experiments included two insect-susceptible control entries ('Beauregard' and 'SC1149-19') and three insect-resistant control cultivars ('Regal,' 'Ruddy,' and 'Sumor'). At each location, genotypes differed significantly in the percentage of uninjured roots WDS (wireworm, Diabrotica, Systena) index, the percentage of roots damaged by the sweetpotato weevil (Cylas formicarius (F.)), the percentage of roots damaged by the sweetpotato flea beetle (Chaetocnema confinis Crotch), and the percentage of roots damaged by white grub larvae (including Plectris aliena Chapin and Phyllophaga spp.). 'SC1149-19' had a significantly lower percentage of uninjured roots, a significantly higher WDS index rating, and significantly higher percentages of infestation by flea beetles, grubs, and sweetpotato weevils than most other sweetpotato genotypes in this study. In addition, 43 of 55 genotypes had significantly less overall insect damage than 'Beauregard,' one of the leading commercial orange-fleshed cultivars in the United States. Ten genotypes had significantly less insect injury than 'Picadito,' a commercial boniato-type sweetpotato grown extensively in southern Florida. Many of these sweetpotato genotypes have high levels of resistance to soil insect pests, and they may be useful as sources of insect resistance for use in sweetpotato breeding programs.     

Impact of planting dates and insecticide strategies for managing crucifer flea beetles (Coleoptera: Chrysomelidae) in spring-planted canola

Integration of cultural practices, such as planting date with insecticide-based strategies, was investigated to determine best management strategy for flea beetles (Phyllotreta spp.) (Coleoptera: Chrysomelidae) in canola (Brassica napus L.). We studied the effect of two spring planting dates of B. napus and different insecticide-based management strategies on the feeding injury caused by fleabeetles in North Dakota during 2002-2003. Adult beetle peak emergence usually coincided with the emergence of the early planted canola, and this resulted in greater feeding injury in the early planted canola than later planted canola. Use of late-planted canola may have limited potential for cultural control of flea beetle, because late-planted canola is at risk for yield loss due to heat stress during flowering. Flea beetle injury ratings declined when 1) the high rate of insecticide seed treatment plus a foliar insecticide applied 21 d after planting was used, 2) the high rate of insecticide seed treatment only was used, or 3) two foliar insecticide sprays were applied. These insecticide strategies provided better protection than the low rates of insecticide seed treatments or a single foliar spray, especially in areas with moderate-to-high flea beetle populations. The foliar spray on top of the seed treatment controlled later-emerging flea beetles as the seed treatment residual was diminishing and the crop became vulnerable to feeding injury. The best insecticide strategy for management of flea beetle was the high rate of insecticide seed treatment plus a foliar insecticide applied at 21 d after planting, regardless of planting date.     

Effect of nitrogen on resistance of sweet potato to sweetpotato weevil (Coleoptera: Curculionidae) and on storage root chemistry.

The effects of nitrogen fertilizer on sweet potato, Ipomoea batatas (L.) Poir., resistance to the sweetpotato weevil, Cylas formicarius elegantulus (Summers), was studied. Adult weevil feeding and oviposition preference, larval survival, and pupal weight were used as measures of sweet potato resistance. Sweet potato resin glycosides and caffeic acid concentrations in the periderm tissue of storage roots also were measured. Sweet potato genotypes (Beauregard, Excel, W-244, W-250, and Sumor) with varying levels of resistance to sweetpotato weevil were grown in the field under three nitrogen regimes (0, 45, and 135 kg N/ha). Harvested storage roots were evaluated in the laboratory for feeding and oviposition activity of sweetpotato weevil female adults under no-choice and choice test conditions. Larval survival rate and pupal weight were determined by rearing the insects individually on storage root sections. Nitrogen level had a significant effect on the number of eggs deposited, but not on the number of feeding punctures. Sweetpotato weevils laid fewer eggs on plants with the highest level of nitrogen. Nitrogen levels did not significantly affect larval survival and pupal weight. Genotype had a significant effect on feeding, oviposition, and larval survival. Beauregard had higher levels of feeding, oviposition, and larval survival compared with the other genotypes. No interaction effects between nitrogen and genotype were significant. Resin glycosides and caffeic acid concentrations were significantly different among genotypes and between years. Nitrogen levels significantly affected the concentrations of caffeic acid in 1997.     

Potential resistance of crape myrtle cultivars to flea beetle (Coleoptera: Chrysomelidae) and Japanese beetle (Coleoptera: Scarabaeidae) damage

Field and laboratory studies were conducted to identify potential resistance among crape myrtles, Lagerstroemia spp., to Japanese beetle, Popillia japonica Newman and to flea beetles, Altica spp. Damage ratings revealed variation among cultivars in susceptibility to beetle feeding. Cultivars with Lagerstroemia fauriei Koehne in their parentage exhibited the least amount of damage in choice and no-choice experiments, with few exceptions. The data indicate that both beetle species cause more feeding damage on certain cultivars of Lagerstroemia indica L., such as 'Country Red', 'Twilight', and 'Carolina Beauty' than interspecific cultivars with L. fauriei in their parentage, such as 'Natchez', 'Tonto', and 'Muskogee'. When comparing the effect of parentage on all of the major pests of crape myrtle, L. faurei confers resistance to all pests except crape myrtle aphid. No correlation was found between leaf toughness, leaf color, and leaf nutrients in estimating flea beetle cultivar preference. With this information, growers can more effectively target scouting measures to the most susceptible cultivars. and breeders can select plants that will require the fewest chemical inputs.     

Influence of preceding crop on wireworm (Coleoptera: Elateridae) abundance in the coastal plain of North Carolina

Three studies were conducted to determine the effect of preceding crop on wireworm (Coleoptera: Elateridae) abundance in the coastal plain of North Carolina. In all three studies, samples of wireworm populations were taken from the soil by using oat, Avena sativa L., baits. Treatments were defined by the previous year's crop and were chosen to reflect common crop rotations in the region. Across all three studies, eight wireworm species were recovered from the baits: Conoderus amplicollis (Gyllenhal), Conoderus bellus (Say), Conoderus falli (Lane), Conoderus lividus (Degeer), Conoderus scissus (Schaeffer), Conoderus vespertinus (F.), Glyphonyx bimarginatus (Schaeffer), and Melanotus communis (Gyllenhal). The effect of corn, Zea mays L.; cotton, Gossypium hirsutum L.; fallow; soybean, Clycine max (L.) Merr.; sweet potato, Ipomoea batatas (L.) Lam.; and tobacco (Nicotiana spp.) was evaluated in a small-plot replicated study. M. communis was the most frequently collected species in the small-plot study and was found in significantly higher numbers following soybean and corn. The mean total number of wireworms per bait (all species) was highest following soybean. A second study conducted in late fall and early spring assessed the abundance of overwintering wireworm populations in commercial fields planted to corn, cotton, peanut (Arachis hypogaea L.), soybean, sweet potato, and tobacco in the most recent previous growing season. C. lividus was the most abundant species, and the mean total number of wireworms was highest following corn and soybean. A survey was conducted in commercial sweet potato in late spring and early summer in fields that had been planted to corn, cotton, cucurbit (Cucurbita pepo L.), peanut, soybean, sweet potato, or tobacco in the most recent previous growing season. C. vespertinus was the most abundant species, and the mean total number of wireworms per bait was highest following corn.     

Differences in Phyllotreta cruciferae and Phyllotreta striolata (Coleoptera: Chrysomelidae) responses to neonicotinoid seed treatments

Insecticidal seed treatments are used commonly throughout the Northern Great Plains of North America to systemically protect seedlings of canola (Brassica napus L. and Brassica rapa L.) from attack by the flea beetles Phyllotreta cruciferae (Goeze) and Phyllotreta striolata (F.) (Coleoptera: Chrysomelidae). Here, we investigated differential responses by the two flea beetle species to the neonicotinoid seed treatments thiamethoxam (Helix and Helix XTra) and clothianidin (Prosper 400) in greenhouse experiments. P. cruciferae experienced higher mortality and fed less when exposed to these compounds than did P. striolata. Beetles of the overwintered and the summer generations responded differently when feeding on seedlings that developed with insecticidal seed treatments, with mortality higher for P. cruciferae in May than in August. When the two flea beetle species were held together at equal densities and allowed to feed on seedlings affected by the seed treatments, mortality of P. cruciferae significantly exceeded that of P. striolata. Differences in efficacies of these compounds for these beetles have ramifications for management strategies in regions where these insects occur sympatrically. Competitive release of P. striolata was previously reported to occur when P. cruciferae was excluded from brassicaceous crops; consequently, the consistent use of these seed treatments over millions of hectares of canola cropland may be a factor that contributes to a shift in prevalence of flea beetle pest species from P. cruciferae toward P. striolata.     

Effects of seeding date and canola species on seedling damage by flea beetles in three ecoregions

Flea beetles ( Phyllotreta striolata (Fabricius), Phyllotreta cruciferae (Goeze) and Psylliodes punctulata Melsheimer) (Coleoptera: Chrysomelidae) are chronic threats to canola seedling establishment throughout the Northern Great Plains of North America. We conducted field studies in AB, Canada, from 2001 to 2004 at Lethbridge, Lacombe and Beaverlodge in the southern, central and northern regions of the province, respectively, to assess the impacts of seeding date (fall, April, May), and canola species ( Brassica rapa L., Brassica napus L.) on flea beetle damage to canola. Flea beetle damage was generally low at Lacombe but reached economic threshold levels at other sites. Although our results were not consistent in all years, seeding date had opposite effects on flea beetle damage to canola seedlings at the southern and northern sites. In the south, both canola species planted in April escaped flea beetle damage unlike the May-seeded plots, which required insecticide spraying in 2003. The numbers of flea beetles on sticky cards sampled during the seedling stage of canola were also lower in early-planted plots than in those planted in May. In the north, flea beetle damage was lower in the May-planted plots compared with those planted earlier. To maximize yields, canola growers need to plant as early as possible in all agro-ecoregions; our study showed that crops in the central and northern regions will be at greater risk of flea beetle damage than in southern regions.     

Arthropod prey of imported fire ants (Hymenoptera: Formicidae) in Mississippi sweetpotato fields

The red imported fire ants, Solenopsis invicta (Buren), are generally considered pests. They have also been viewed as beneficial predators feeding on other insect pests of various agroecosystems. This study documents the foraging habits of fire ants in a sweetpotato field in Mississippi. Fire ant foraging trails connecting outside colonies to a sweetpotato field were exposed and foraging ants moving out of the field toward the direction of the colony were collected along with the solid food particles they were carrying. The food material was classified as arthropod or plant in origin. The arthropod particles were identified to orders. Fire ant foragers carried more arthropods than plant material. Coleoptera and Homoptera were the most abundant groups preyed upon. These insect orders contain various economically important pests of sweetpotato. Other major hexapod groups included the orders Hemiptera, Diptera and Collembola. The quantity of foraged material varied over the season. No damage to sweetpotato roots could be attributed to fire ant feeding. Imported fire ant foraging may reduce the number of insect pests in sweetpotato fields.     

Alternative management tactics for control of Phyllotreta cruciferae and Phyllotreta striolata (Coleoptera: Chrysomelidae) on Brassica rapa in Massachusetts

The flea beetles Phyllotreta cruciferae (Goeze) and Phyllotreta striolata (F.) (Coleoptera: Chrysomelidae: Alticinae) are significant pests of crops in the Brassicaceae family. From 2001 to 2003, the efficacy of both new and commonly used treatments for the control of flea beetles in brassicas, Brassica rapa L., were evaluated in three small plot, randomized complete block design trials. Row cover and carbaryl (applied as a weekly foliar spray) were found to be the most consistent at reducing damage in comparison with untreated controls in all trials. Two new products that may provide adequate flea beetle control are spinosad (in either conventional or organic formulations) and thiamethoxam. The plant-derived compounds azidiractin and pyrethrin did not protect treated plants from flea beetle feeding. Treatment of plants with kaolin, or removal of the beetles with a vacuum, also did not reduce the level of crop damage. The level of damage at harvest was found to be correlated with population size of flea beetles in each plot, as measured by captures on yellow sticky traps and direct visual counts. Removal of the outer two leaves of individual B. rapa plants reduced the total number of holes per plant by 40%, while only removing 15% of the leaf area.     

Comparative evaluation and economic potential of ecorational versus chemical insecticides for crucifer flea beetle (Coleoptera: Chrysomelidae) management in Canola

From 2001 to 2004, field studies were conducted to evaluate the effect of the ecorational insecticides SpinTor (spinosad), BotaniGard (Beauveria bassiana), Neemix (azadirachtin), and Surround (kaolin) against crucifer flea beetle on canola, Brassica napus L., at the cotyledon stage. The ecorational treatments were compared with a standard foliar chemical insecticide, Capture (bifenthrin), and the chemical seed treatment insecticide Helix XTra (thiamethoxam). This study indicated that flea beetle injury was lower for Helix XTra, Capture, and the ecorational insecticide SpinTor. SpinTor was less effective when flea beetle populations were relatively high (200-300 per trap-week). Yields for chemical insecticide treatments were always greater than SpinTor, with differences being the smallest (68-374 kg/ha) at low levels of flea beetle feeding injury. Differences were greatest when canola seedling injury was high (775-1,364 kg/ha). Yield differences between the conventional insecticides and BotaniGard, Neemix, and Surround were 119-439 and 61-2,248 kg/ha at low and high flea beetle feeding injury, respectively. Although yield differences between SpinTor and chemical insecticides were relatively small at lower levels of flea beetle injury, net losses ranged from $47 to $151/ha when SpinTor was used as an alternative to a standard chemical seed treatment, Helix XTra. This suggests that SpinTor would not be a viable alternative to the chemical insecticide. Net losses ranged from $30 to $266/ha when BotaniGard, Neemix, and Surround were used as alternatives to the seed treatment.     

Resistance of sweetpotato genotypes to adult Diabrotica beetles

Production of sweetpotatoes, Ipomoea batatas (L.) Lam. (Convolvulaceae), is limited by several insect pests, including Diabrotica spp. (Coleoptera: Chrysomelidae), and new integrated pest management (IPM) techniques for this crop are needed. Host plant resistance is one attractive approach that fits well into IPM programs. A host plant resistance research program typically depends on reliable bioassay procedures to streamline evaluation of germplasm. Thus, a bioassay technique was developed for evaluating sweetpotato germplasm by using adults of the banded cucumber beetle, Diabrotica balteata LeConte, and spotted cucumber beetle, Diabrotica undecimpunctata howardi Barber. A single beetle was placed on a piece of sweetpotato peel (periderm and cortex with stele removed) that was embedded periderm-side up in plaster in a petri dish. Feeding and longevity of insects on 30 sweetpotato genotypes were evaluated in two experiments by using this procedure. Adult longevity ranged from 7 to 11 d for starved individuals to 211 d for beetles fed a dry artificial diet. Longevity of banded cucumber beetles that fed on sweetpotato peels ranged from 12 d for the most-resistant genotype to 123 d for SC1149-19, a susceptible control cultivar. Longevity of spotted cucumber beetles was slightly shorter than longevity of banded cucumber beetles. For the most resistant sweetpotato genotypes, both Diabrotica species exhibited a significant delay in initiation of feeding, and more beetles died on these genotypes before they had fed. Both antibiosis and nonpreference (antixenosis) are important mechanisms of resistance in sweetpotato genotypes. This bioassay was consistent with field results, indicating that this technique could be useful for evaluating resistance to Diabrotica spp. in sweetpotato genotypes.     

Comparative susceptibility of sweetpotato weevil (Coleoptera: Brentidae) to selected insecticides

The response of sweetpotato weevil, Cylas formicarius (F.) (Coleoptera: Brentidae), to insecticides used for its control was tested in laboratory bioassays. A glass vial bioassay technique was used to determine the susceptibility of two cohorts of sweetpotato weevil to selected insecticides. Vials were treated with methyl parathion, bifenthrin, cyfluthrin, carbaryl, and phosmet. Sweetpotato weevils demonstrated a mortality response to increasing concentrations of all insecticides tested, and our results indicated decreases in susceptibility of the Louisiana cohort of sweetpotato weevil compared with the Texas cohort for all insecticides tested. Methyl parathion was the most toxic chemical tested for both cohorts, followed by the pyrethroids, cyfluthrin and bifenthrin. Phosmet exhibited moderate toxicity compared with other chemicals tested, whereas sweetpotato weevils were least susceptible to carbaryl. Significant differences in lethal concentration (LC)50 and LC90 values for cyfluthrin and bifenthrin, the LC50 values for methyl parathion and phosmet, and the LC90 values for carbaryl were observed between the two cohorts. This study documents baseline toxicological data for five insecticides in two populations of sweetpotato weevil and demonstrates that susceptibility to all insecticides tested is lower for the Louisiana population compared with the Texas population.     

Phyllotreta cruciferae and Phyllotreta striolata responses to insecticidal seed treatments with different modes of action

The strategy used most commonly in western North America to protect seedlings of canola (Brassica rapa L. and Brassica napus L.) from attack by adults of the flea beetles Phyllotreta cruciferae (Goeze) and Phyllotreta striolata (Fabricius) (Coleoptera: Chrysomelidae) involves planting seed coated with insecticide for systemic activity. Previous research determined that the two beetle species responded differently to the most commonly used neonicotinoid seed dressings. However, other insecticides that exploit different modes of action have commercial potential for managing infestations of these pests, but no information exists on their efficacies for these flea beetle species. Studies were conducted to compare effects of the neonicotinoid compounds, thiamethoxam and imidacloprid, to spinosyn and fipronil as systemic seed treatments for reducing feeding damage to canola seedlings and increasing mortality of P. cruciferae and P. striolata. Phyllotreta cruciferae experienced greater mortality and caused less feeding damage than P. striolata to seedlings treated with the neonicotinoid compounds. Mortality increased and feeding damage decreased significantly when beetles fed upon seedlings treated with fipronil, indicating its potential usefulness for control of these pests. However, spinosyn seed treatment was relatively ineffective against either beetle species. Higher rates of P. striolata mortality with fipronil than thiamethoxam suggest that fipronil may provide improved flea beetle control over hundreds of thousands of hectares in western North America where flea beetle populations are dominated by P. striolata, and control with thiamethoxam has been suboptimal.     

Feeding by flea beetles (Coleoptera: Chrysomelidae; Phyllotreta spp.) is decreased on canola (Brassica napus) seedlings with increased trichome density

Laboratory and field studies were undertaken to determine the effects of increased numbers of trichomes on seedling stems, petioles, and first true leaves of Brassica napus L., canola, on the feeding and behavior of the crucifer flea beetle Phyllotreta cruciferae (Goeze) (Coleoptera: Chrysomelidae). Seedlings of 'Westar' canola with genes inserted from Arabidopsis thaliana L. for increased trichome production, called Hairyl, were tested against Westar seedlings in no-choice and choice laboratory tests, and against parental plants and other cultivars grown from seed with and without insecticide in field trials at Saskatoon and Lethbridge, Canada. Analyses ofprefeeding and feeding behavior in no-choice tests of first true leaves found that flea beetles interacted with their host while off Hairyl leaves more so than beetles presented with leaves of Westar. Beetles required twice as much time to reach satiation when feeding on leaves with increased pubescence than on Westar leaves. In laboratory choice tests, flea beetles fed more on cotyledons and second true leaves of Westar than on comparable tissues of the transgenic line. In field trials, variations in feeding patterns were seen over time on cotyledons of the line with elevated trichomes. However, all four young true leaves of Hairyl seedlings were fed upon less than were the parental lines. Feeding on Hairyl plants frequently occurred at levels equal to or less than on cultivars grown from insecticide-treated seed. This study highlights the first host plant resistance trait developed in canola, dense pubescence, with a strong potential to deter feeding by crucifer flea beetles.     

Effect of crop rotation on populations of Epitrix tuberis (Coleoptera: Chrysomelidae) in potato

The effect of crop rotation on populations of tuber flea beetle, Epitrix tuberis Gentner, in potatoes was investigated using data supplied by an integrated pest management (IPM) company and Geographic Information System software and conventional statistical methods. Using combined 1995 and 1996 data, beetles of the overwintered and F1 generations in both the interior and edges of potato fields showed a significant linear increase with an increase in the preceding consecutive years (0, 1, and 2 years) that the current years' crop was planted to potatoes. Populations were significantly higher in nonrotated fields compared with rotated fields. Both the percentage of the cropping region requiring insecticidal control of tuber flea beetles and the cost of insecticides per hectare of potatoes grown increased linearly with an increase in the number of previous years planted to potatoes. Not practicing crop rotation resulted in a 4.2-7.3% increase in the cropping region requiring insecticidal control of tuber flea beetles. The cost of controlling beetles in potato fields planted to potatoes for 3 consecutive years was up to $20/ha greater than potatoes rotated from the preceding year. Beetle counts from the interior of rotated potato fields never exceeded threshold levels when field edges also were below threshold. It is concluded that sampling of overwintered beetles in interior sites of rotated fields could be abandoned, and only 1 monitoring scout rather than 2 would be necessary to monitor a field during this time. From these results, we concluded that rotating potato crops would reduce spray costs to the farmer and monitoring costs to IPM companies.     

Evaluation of cucurbitacin-based gustatory stimulant to facilitate cucumber beetle (Coleoptera: Chrysomelidae) management with foliar insecticides in melons

The bitter plant-derived compounds cucurbitacins are known to stimulate feeding of adult cucumber beetles (Coleoptera: Chrysomelidae). A cucurbitacin-based gustatory stimulant applied as a flowable bait combined with either spinosad or carbaryl was compared with foliar sprays of spinosad and carbaryl for controlling two cucumber beetle species (Diabrotica undecimpunctata undecimpunctata Mannerheim and Acalymma trivittatum Mannerheim) in honeydew melons (Cucumis melo L.). Field studies were conducted on the University of California-Davis plant pathology farm in 2008 and 2009. Beetle densities after applications and fruit damage from beetle feeding were compared among treatments. In addition, beetle survival was compared within field cages placed over the treated foliage infested with beetles. Using all three measures of efficacy, we determined that the addition of cucurbitacin bait had no effect on the level of cucumber beetle control with carbaryl in either 2008 or 2009. In both years, spinosad did not significantly reduce cucumber beetle densities in either field cages or field plots and did not reduce fruit damage relative to the untreated control. The addition of the bait to spinosad did not improve its efficacy. A laboratory bioassay of the spinosad formulation used in the field showed it had significant lethal effects on adults of both cucumber beetle species. Results indicated that the bait formulation used did not improve cucumber beetle control but may benefit from the addition of floral attractants or using a different type of cucurbitacin.     

入侵害虫甘薯凹胫跳甲的鉴定及线粒体基因组分析

【目的】基于形态学鉴定和分子生物学技术确认甘薯凹胫跳甲Chaetocnema confinis是否入侵中国大陆,测定甘薯凹胫跳甲线粒体基因组序列,分析基因组结构及其系统发育关系。【方法】应用显微镜观察从广东不同地点采集的甘薯凹胫跳甲成虫的形态特征,并扩增cox1基因DNA序列进行分子鉴定;利用Illumina MiSeq测序平台对甘薯凹胫跳甲线粒体基因组进行测序、拼装、注释和特征分析;基于亲缘关系相近种属的线粒体基因组序列进行共线性分析和构建系统发育树,分析基因重排和系统发育关系。【结果】形态和分子鉴定结果表明大陆甘薯上发现的跳甲为甘薯凹胫跳甲。甘薯凹胫跳甲线粒体基因组序列大小为15 685 bp,包括有13个蛋白质编码基因、2个rRNA基因、22个tRNA基因和1个非编码控制区;这37个基因之间排列紧凑,间隔总长度101 bp,排列顺序与模式昆虫Drosophila yakuba线粒体基因排列顺序相同。甘薯凹胫跳甲线粒体基因组A+T含量为77.3%,具有明显的AT偏向性。13个蛋白质编码基因的起始密码子均为ATN。在22个tRNA基因中除trnS1的DHU臂缺失,trnD, trnG, trnN和trnT的二级结构中缺少TψC环外,其余17个都能形成典型的三叶草式二级结构,另trnK的反密码子突变为UUU,trnS1的反密码子突变为UCU。甘薯凹胫跳甲的控制区片段长度仅有60 bp,是目前已报道的昆虫线粒体基因组中最短的控制区。基于线粒体基因组的系统发育分析表明,甘薯凹胫跳甲与跳甲亚科(Alticinae)黄曲条跳甲Phyllotreta striolata亲缘关系最近。【结论】甘薯凹胫跳甲已经入侵到中国大陆。本研究获得了甘薯凹胫跳甲的线粒体基因组序列,为防控甘薯凹胫跳甲和分析叶甲科(Chrysomelidae)各种属间的系统发育关系奠定了基础。     

Aggregation and mortality of Agriotes obscurus (Coleoptera: Elateridae) at insecticide-treated trap crops of wheat

Agriotes obscurus (L.) wireworms assembled in increasing numbers at rows of treated (Agrox DL Plus seed treatment) and untreated wheat, Triticum aestivum L., planted at increasing densities (0, 0.15, 0.30, and 0.60 seeds/cm). In treated wheat plots at all planting densities, no wireworm damage to seedlings was apparent, and total wireworms taken in core samples in wheat rows increased according to the asymptotic equation y = B0(1 -e(-Blx)), where B0 is the asymptote, B1 is the slope of the initial rise, and x is the seeding density. The number of dead wireworms in treated plots increased linearly and intercepted the asymptotic models (theoretical point at which 100% mortality of assembled population occurs) at 0.95 seeds/cm on 11 June and 1.14 seeds/cm on 18 June 1996. Untreated wheat at all densities planted had severe wireworm damage and significantly reduced stand. Populations that had assembled at the surviving untreated wheat were fewer than in the treated wheat plots, and although increasing with seeding density, did not follow the asymptotic model. The data suggest that A. obscurus populations can be assembled and killed in fallowed fields in large numbers at treated trap crops of wheat over a 19-d period when planted in rows spaced 1 m apart at a linear seeding density of 1.5 seeds/cm.