Charlet, Laurence D.

Glogoza, Phillip A.

Knodel, Janet J. (Janet Jean), 1958-

English

NDSU Libraries Institutional Repository

The sunflower beetle, Zygogrammaexclamationis (Fabricius), is one ofthe major economic insect pests ofsunflower in the northern plains. It is nativeto North America and has moved fromfeeding on wild sunflowers to becomethe major defoliating pest of cultivatedsunflower. The insect belongs to the familyChrysomelidae (leaf-feeding beetles), thegroup which also includes the destructiveColorado potato beetle. The sunflowerbeetle is found throughout the Great Plainswherever sunflower is grown. Both theadult and larval stages consume leaftissue, which can result in yield reductionof sunflower seed (Figure 1). Although thesunflower beetle is present each year, theseverity of infestation varies. During yearswith heavy infestations, the sunflowerbeetle was ranked as the worst insect pestproblem by most North Dakota sunflowerproducers, with approximately 60 percentof the sunflower acreage being treated tomanage either the adult or larval stage.DistributionThis insect has been reported fromsouthern Canada to northern Texas,Arizona, New Mexico, and west to Utah.High populations often necessitate controlmeasures in cultivated sunflower grown inNorth and South Dakota and Minnesota.Although present in the central and south-E-824 (Revised)BIOLOGY AND PEST MANAGEMENT OF THESunflower Beetlein North DakotaJanet J. Knodel, Crop Protection SpecialistLaurence D. Charlet, USDA, ARS Research EntomologistPhillip A. Glogoza, Extension EntomologistFigure 1. Sunflower plant damaged by sunflower beetle.North Dakota State UniversityFargo, North Dakota 58105MARCH 20002ern plains, the sunflower beetle has notbeen considered a serious pest of culti-vated sunflower in these regions.IdentificationAdult: The head of the adultis reddish-brown and thethorax (area between headand abdomen) is pale cream-colored with a reddish-brown patch at thebase (Figure 2). Each wing cover is cream-colored and has three dark stripes thatextend its length. A shorter lateral stripeends at the middle of the wing in a smalldot that resembles an exclamation point.The beetle is 1/4 to 1/2 inch (6 to 12 mm)long and 3/32 to 3/16 inch (2 to 4 mm)wide.Eggs: Eggs are about 1/16inch (1.5-2.0 mm) long, cigar-shaped and cream-yellow incolor (Figure 3).Larvae: Sunflower beetlelarvae are yellowish-greenwith a brown head capsuleand humpbacked in appear-ance. Newly hatched larvae are about 1/16inch (1.5-1.75 mm long), and will reach alength of about an inch (8-10 mm) whenfully developed (Figure 4).Pupae: Pupae are similar in size tothe adult and yellow in color.Life Cycle (Figure 5)The sunflower beetle has one genera-tion per year in the northern plains. Adultsoverwinter in the upper 2 to 4 inches (5-10cm) of soil and emerge from the previoussunflower fields in May to early June.Beetles overwinter throughout the field andexhibit no preference for field edges orshelterbelts. Research indicates that adegree day (DD) model and calendardates are equally accurate in predicting theonset and 50 percent emergence of thesunflower beetle population. The DD modelis initiated on March 1st and is based onsoil temperature at a depth of 2 inches(5 cm) and a base of 32oF (0oC). Sunflowerbeetles begin to emerge at a mean of 416DD oF (232 DD oC), and 50 percent of theadult emergence occurs by 710 DD oF(395 DD oC).Shortly after emergence the beetlesbegin to feed, mate and lay single eggs onstems and undersides of leaves. Adults livefor about 8½ weeks and lay eggs for a 6-7week period. Each female lays approxi-mately 850 eggs with a range of 200-2,000eggs. About 14 eggs per day are laid. Eggsurvival is about 70 percent in the labora-tory but is estimated at only 50 percent inthe field. Some eggs fail to hatch due topredation, egg sterility, and unfavorableweather conditions like hot, sunny weather.Eggs hatch into larvae in about one week.The larvae have four instars, which feedand are present in fields for about sixweeks. When mature, larvae drop to thesoil where they pupate in earthen cells.The pupal stage lasts from 10 days to twoweeks. A new generation of adults (calledthe summer generation) emerge in lateJuly through early September and feed fora short period on the uppermost leaves orbracts of sunflower before burrowing backinto the soil to overwinter. Feeding by thesummer generation adults causes minimaldamage to the maturing sunflower plant.These adults do not mate or lay eggs untilthe following spring.Figure 2. Sunflower beetle adult.Figure 4.Sunflower beetle larvae.Figure 3.Sunflowerbeetle egg.3HostsSunflower beetles are generallyrestricted to cultivated or wild sunflowerand a few close relatives. Adults and larvaeare observed on wild sunflower includingHelianthus annuus L., H. petiolaris Nuttall,H. nuttallii Torrey and Gray, H. pauciflorusNuttall, H. maximiliani Schrader, H.tuberosus L., and H. giganteus L. In Texas,they have also been found on woolly leafbursage, Franseria tomentosa Gray.Crop DamageDamage due to adult feeding beginssoon after beetles emerge from hiberna-tion. They seldom feed on the cotyledons,but the first true leaves may be severelydamaged or completely consumed. Ifbeetles are abundant, fields may beseverely defoliated. Adults feed predomi-nately on leaf margins while larvae feedover the entire leaf surface. When larvaeare numerous, damaged leaves take on alacy appearance. Damage may be mostnoticeable in field margins. Most larvalfeeding occurs at night, and adults will feedduring the day. During the daytime, larvaetypically rest in the terminal growth areawhere they are easily found in leaf andflower buds. If larval feeding is severe,defoliation can reduce yield by poor seedset or fill.The late summer generation ofemerging sunflower beetle adults rarelycauses economic damage to the sunflowercrop. However, in some cases they havebeen abundant enough to cause feedinginjury on late-planted sunflower.Eggs laid in stems Larvae feed onupper foliage Pupation in soil Adults of this seasonAdults overwinterin the soilAdults fromprevious seasonMAY JUNE JULY AUGUST SEPTEMBER OCTOBERNOVEMBERAPRIL WINTERFigure 5. Life cycle of the sunflower beetle.4Pest ManagementIn the spring, overwintering sunflower beetle adults emerge, locate, feed,mate, lay eggs, and damage emerging sunflower plants. To effectivelymanage sunflower beetles, producers should use an Integrated PestManagement (IPM) Program. This type of approach can maximize yieldsand profits and minimize losses. Sunflowers should be monitored on aregular basis to determine the level of infestation and damage. Tominimize inputs, to conserve the natural enemies of the sunflower beetle,and to reduce the negative impacts of pesticides on the environment,insecticides are only recommended when beetle populations havereached the “economic threshold level.”Cultural ControlCultural control manages insect pestsby altering farming practices, is compatiblewith conserving natural enemies, and isenvironmentally friendly. Two differentcultural strategies that have been studiedfor sunflower beetle management are:Planting DateFor the sunflower beetle, adult andlarval populations decrease as plantingdate is delayed. Defoliation is also lowest inthe latest planting date. As a result, delayedplanting was effective in preventing yieldreductions caused by sunflower beetlefeeding. A further benefit was that nonegative impacts were observed on theparasitism rate of the tachinid fly,Myiopharus macellus (Rheinhard), whichattacked the sunflower beetle larvaeequally in all of the different planting dates.Delayed planting also has been shown toreduce losses (seed weight or oil content)caused by the sunflower stem weevil(Cylindrocopturus adspersus (LeConte))and the banded sunflower moth (Cochylishospes Walsingham). But, damage fromthe red sunflower seed weevil (Smicronyxfulvus LeConte) tends to be greater in later-planted fields. Thus, sunflower plantingdecisions need to be based on the histori-cal pest problems for a particular area. Inaddition, growers should consider thatsunflower fields planted late (early June)usually have lower yields than fieldsplanted early (mid to late May).Tillage/CultivationResearch has demonstrated thatspring or fall cultivation does not reducethe overwintering populations of sunflowerbeetle adults or influence the pattern ofemergence from the soil during the springand summer. However, another sunflowerpest, the red sunflower seed weevil, isnegatively affected by tillage, whichreduces emergence of adult seed weevils.Plant ResistanceAs yet, sunflower hybrids with resis-tance to the sunflower beetle have notbeen developed. Studies with about 20species of native sunflowers have shownthe genetic basis for resistance is presentin some of these species. The resistancemechanisms exhibited in these nativespecies include both antibiosis, in whichlarval mortality is higher when feeding onthe plants, or antixenosis (non-preference),which is evident in reduced feeding byadults and larvae. In some cases, adultlongevity was reduced and females laid no5eggs. Although not killed outright, develop-ment time of beetles when feeding onsome wild species was lengthened andtheir weights were reduced. The reducedvigor of these low-weight beetles makesthem more vulnerable to attack by theirnatural enemies in the field.Biological ControlThe sunflower beetle has a number ofnatural enemies that either directly con-sume the various stages of the beetle orparasitize these stages with the progeny ofthe parasitoid destroying the beetle egg,larva or adult. Since these natural enemiesare present in sunflower fields, it is impor-tant to protect them from unnecessaryapplications of pesticides which will killthem along with the sunflower beetles. Byapplying insecticides only when the pestdensity reaches the economic threshold,the predators and parasitoids are protectedand allowed to serve as natural controlagents for the sunflower beetle.PredatorsMany different insect predators feedon the different life stages of the sunflowerbeetle. Sunflower beetle eggs are eaten bythe melyrid beetle, Collops vittatus Say, thethirteen spotted lady beetle, Hippodamiatredecimpunctata tibialis (Say), and theconvergent lady beetle, H. convergensGuerin-Meneville. Larvae of the commongreen lacewing, Chrysoperla carneaStephens, consume both eggs and larvae.The spined soldier bug, Podiusmaculiventris (Say), has been seen feedingon adults and larvae in North Dakota. Thetwospotted stink bug, Perillus bioculatus(Fabricius) (Figure 6), has been observedfeeding on sunflower beetle larvae inManitoba, Texas, and North Dakota. InNorth Dakota, a more rare, related stinkbug species (Perillus circumcinctus Stal) isalso present in sunflower fields and feedson beetle larvae. The carabid beetle, Lebiaatriventris Say, was reported to feed onsunflower beetle larvae in Manitoba andTexas (Figure 7). It appears to be a com-mon inhabitant of sunflower fields in NorthDakota and Minnesota. Laboratory studieshave shown it to be a voracious feeder onsunflower beetle larvae. In Manitoba,damsel bugs, Nabis sp., were the fourthmost common predator in sunflower fieldsand were suspected of feeding on sun-flower beetle larvae. These predators arealso common in North Dakota sunflowerfields.Although they are a serious pest ofsunflowers in many areas of the state atcertain times of the year, redwingedblackbirds also feed on sunflower beetleadults. A variety of spider species arecommon inhabitants of cultivated fields andundoubtedly consume adults and larvae ofthe sunflower beetle.Figure 6a. Predator of sunflower beetle: adulttwospotted stink bug, Perillus bioculatus(Fabricius).Figure 6b. Nymphs of twospotted stinkbug, Perillus bioculatus (Fabricius) feedingon a sunflower beetle larva.Figure 7. Predator of sunflower beetle: adult carabidbeetle, Lebia atriventris Say.6ParasitoidsParasitoids attack sunflower beetleeggs, larvae, and adults. Eggs are parasit-ized by the pteromalid wasp, Erixestuswinnemana Crawford, in North Dakota,Minnesota, and Manitoba. Reported para-sitism rates are much lower in the U.S.(1 percent) than in Canada (17 percent).Larvae are parasitized by two species ofparasitic flies of the family Tachinidae,Myiopharus macellus and M. doryphorae(Riley) in Manitoba, North Dakotaand Minnesota (Figure 8). Myiopharusdoryphorae has only been recovered fromCanada and is extremely rare, constitutingless than 1 percent of parasitoids rearedfrom sunflower beetle larvae. The lifehistory of M. macellus is well synchronizedwith the life cycle of its host, and the rate ofparasitization is high in some fields in bothCanada and the U.S. (up to 70 and 100percent, respectively). The fly develops inthe beetle larva, kills the larva when itmoves into the soil to pupate, and emergesfrom the soil. Since the sunflower beetleoverwinters as an adult, the fly must eitheroverwinter in an alternate host or move intothe northern plains from southern areaseach year. Adult sunflower beetles areparasitized by the tachinid, Myiopharus sp.Approximately 0.2 to 17 percent of adultsin Manitoba are attacked, but studies haveshown that less than 2 percent are para-sitized in North Dakota and Minnesota.Chemical ControlMonitoringField scouting is necessary to deter-mine whether or not a field needs to betreated. When monitoring a field, count thenumber of adults and/or larvae on 20plants at five randomly selected samplingsites throughout the field for a total of 100plants. Use a “X” pattern and selectsampling sites at least 75 to 100 feet fromthe field margins. Determine the averagenumber of adults and/or larvae per plant.Estimate the percent defoliation (Figure 9)during field scouting.Economic ThresholdsSeedling:1 to 2 adult(s) per seedlingLater plant growth stages(vegetative to reproductive):1 to 2 adult(s) per plant10-15 larvae per plantOR25 to 30 percent foliar defoliationon the top 10-15 leaves or the“active growing part”In the seedling stage, one-two adultsper seedling is the recommended eco-nomic threshold. As sunflower plantsdevelop, they can tolerate more feedingdamage. When populations reach 10 to 15larvae per plant, approximately 25 percentdefoliation on the upper eight-12 leavesoccurs. When adult populations averagetwo adults per plant, enough larvae areoften produced to cause yield losses of 20percent. Management is normally advisedif defoliation reaches the 25 to 30 percentFigure 8. Parasitoidof sunflower beetle:adult tachinid fly,Myiopharus macellus(Rheinhard).7level in late vegetative and early budstages and it appears (based on larval sizeof less than 1/4 inch or 6 mm) that moredefoliation will occur on the actively grow-ing part of sunflower plant. However, ifdefoliation is 25 percent and the majority oflarvae are about 1/3 inch (8 mm) long, theywill have reached maturity and stoppedfeeding. Then management is not bewarranted.Insecticide RecommendationsApplication of an insecticide is recom-mended only when beetle populationshave reached an economic threshold levelin a field. Insecticides are effective inpreventing economic loss when applied toactively feeding adults and/or larvae.Insecticides registered for sunflower beetlemanagement in North Dakota as of 2000are listed in the table below. Please checkwith the current Field Crop Insect Manage-ment Guide for updated insecticide regis-trations. It is of utmost importance thatinsecticide users READ, UNDERSTAND,and FOLLOW ALL LABEL DIRECTIONS.Figure 9. Various levels of percent defoliation (5-50 percent) caused by sunflower beetle feeding.50%45%40%35%30%25%20%15%10%5%NDSU Extension Service, North Dakota State University of Agriculture and Applied Science, and U.S. Department of Agriculture cooperating.Sharon D. Anderson, Director, Fargo, North Dakota. Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. We offerour programs and facilities to all persons regardless of race, color, national origin, religion, sex, disability, age, Vietnam era veterans status,or sexual orientation; and are an equal opportunity employer. 4M-4-00This publication will be made available in alternative format upon request to people with disabilities (701) 231-7881.Insecticide RecommendationsDosage in ProductInsecticide lb ai/acre per acre Restrictions on useAsana XL* 0.015 - 0.03 lb/acre 2.9 - 5.8 fl oz Do not apply within 28 days of harvest.esfenvalerate A reduced rate has been issued as a state 2(ee) label. These lower rates are for control ofRUP SF beetle larvae ONLY. The reduced rateapplication has a range of 1.45 - 5.8 fl oz.Baythroid* 0.025 - 0.044 lb/acre 1.6 - 2.8 fl oz Do not apply within 30 days of harvest.cyfluthrinRUPcarbaryl (Sevin) 1.5 - 2 lb/acre rate varies by Do not apply within 60 days of harvest. Do notformulation allow livestock to graze on treated forage.Furadan 4F* 0.125 - 0.5 lb/acre 0.25 - 1 pt Do not re-enter treated fields within 14 days ofcarbofuran application without wearing proper protectiveRUP clothing. Do not harvest crop within 28 days oflast application.Lorsban 4E 0.5 - 0.75 lb/acre 1 - 1.5 pts Do not apply within 42 days of harvest. Do notchlorpyrifos allow livestock to graze in treated areas.Scout X-TRA* 0.005 - 0.01 lb/acre 0.71 - 1.42 fl oz Do not apply within 21 days of harvest.tralomethrinRUPWarrior T* 0.015 - 0.025 lb/acre 1.92 - 3.2 fl oz Do not apply within 45 days of harvest. Alambda cyhalothrin reduced rate has been issued as a state 2(ee) label. The reduced rate applicationRUP has a range of 1.28 - 2.56 fl oz.*RUP - Restricted use pesticide

Biology and Pest Management of the Sunflower Beetle in North Dakota

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Biology and Pest Management of the Sunflower Beetle in North Dakota

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