Crucifer Flea Beetle Biology and Integrated Pest Management in ...

E-1234CruciferFlea BeetleBiology andIntegrated Pest Managementin CanolaJanet J. Knodel, Crop Protection Extension SpecialistNorth Central Research Extension CenterDenise L. Olson, Research EntomologistNorth Dakota State UniversityFargo, North Dakota 58105SEPTEMBER 2002Canola is an important oilseed crop in thenorthern Great Plains of the United States andCanada. Canola adds crop diversity to thecropping rotation systems in the region.Production has increased in the United States andCanada in response to the pest problems and lowcommodity prices of small grains and increasedmarket demand by health conscious consumersfor its high quality edible oil.The crucifer flea beetle, Phyllotreta cruciferaeGoeze, and the striped flea beetle, Phyllotretastriolata (F.) (Coleoptera: Chrysomelidae),are the most serious insect pests of canola.Both species were introduced from Eurasia.Phyllotreta cruciferae has become the dominantflea beetle pest of oilseed Brassica (canola).Adult flea beetles emerge in the spring and feedon the cotyledons and true leaves. When theyemerge in large numbers, they can quicklydevastate a seedling canola field; therefore,timely detection and management of this pestis important. Flea beetle damage to oilseedBrassica crops exceeds $300 million annuallyin North America.

Figure 1. Adult crucifer flea beetle, Phyllotretacruciferae Goeze.DistributionThe crucifer flea beetle was introduced into NorthAmerica in the 1920s and is now distributed acrosssouthern Canada and the northern Great Plains of theUnited States, including North Dakota, South Dakota,Montana, northwestern Minnesota, Manitoba,Saskatchewan, Alberta, British Columbia, Ontario,Quebec, and New Brunswick. The crucifer flea beetleis the most common and destructive flea beetleattacking canola.In North America, the striped flea beetle wasreported from “Carolina” in 1801 and is nowwidespread across Canada, United States, Mexico,and South America.Figure 2. Adult striped flea beetle, Phyllotretastriolata (F.).Figure 3. Flea beetle egg.Figure 4. Flea beetle larva.IdentificationAdultCrucifer flea beetle (Figure 1): The adult is a small,oval-shaped, blackish beetle with a bright blue sheen onthe elytra, measuring about 1/32 to 1/8 in. (2-3 mm) inlength. Flea beetles have enlarged hind femora (thighs)on their hind legs, which they use to jump quickly whendisturbed. Their name, flea beetle, arose from thisbehavior.Striped flea beetle (Figure 2): Adults are similar insize and shape to the crucifer flea beetle, but they areblack with two yellow strips on their wing covers.Eggs (Figure 3)Eggs are yellow, oval, and about 0.38-0.46 mm longby 0.18-0.25 mm wide, and deposited singly or ingroups of three or four adjacent to the host plant’s roots.Larvae (Figure 4)Larvae are small approximately 1/8 in. or 3 mm,whitish, slender, cylindrical worms. They have tiny legsand a brown head and anal plate.Pupae (Figure 5)Pupae are similar in size to the adult and white incolor except for the black eyes and the free bodyappendages, which are visible later in the pupal development.Figure 5. Flea beetle pupa.2

Life Cycle (Figure 6)Crucifer flea beetles have a single generation in thenorthern Great Plains. They overwinter as adults in theleaf litter of shelterbelts or grassy areas and are rarelyfound in canola stubble. Beetles emerge when temperatureswarm up to 57°F (14°C) in early spring. They feedon volunteer canola and weeds, such as wild mustard,and move to newly planted canola as it emerges.Depending on the temperature, it may take up to threeweeks for the adults to leave their overwintering sites.The striped flea beetle adults usually emerge beforethe crucifer flea beetle. Warm, dry, and calm weatherpromotes flea beetle flight and feeding throughout thefield, while simultaneously slowing canola growth. Incontrast, cool, rainy, and windy conditions reduce flightactivity, and flea beetles walk or hop leading to concentrationsin the field margins. Females oviposit up to 25eggs in the soil in June. The overwintered adultscontinue to remain active until late June and begin todie off in early July. Larvae hatch from the eggs inabout 12 days and feed on the secondary roots of theplant. No major effects on plant vigor from larval rootfeeding have been noted in North Dakota. However,a yield loss of 5% from larval densities of 1/sq. in.(0.16/sq. cm) has been recorded in Manitoba. Larvaepass through three instars and complete their developmentin 25 to 34 days by forming small earthen puparium.The pupal stage lasts for about seven to ninedays, usually in early to mid-July. The new generationof adults emerge from the puparium beginning in lateJuly until early September and feed on the epidermisof green foliage and pods of canola, mustard, andcruciferous weeds (Figure 7). The crop is usuallymature enough that feeding damage is minimal. In earlyfall beetles move to overwintering sites.Figure 6. Life cycle of the Crucifer flea beetle.FallSummer generationof adults July - Oct.WinterSpringOverwintering adultsemergeADULTPUPAJuly - AugustSummerEGGMay - JuneLARVAJune - July3

HostsThe crucifer flea beetle has a narrow host range restrictedto plants primarily in the mustard family(Cruciferae). Other plant families attacked are the caperfamily (Capparidaceae), the nasturtium family(Tropaeolaceae), and the marshflower family(Limnanthaceae). Interestingly, all of the flea beetlesprefer plant families that produce mustard oil (or allylisothiocyanate), which is a known aggregation pheromoneof the crucifer flea beetle. The most-preferredhosts are in the genus Brassica (Cruciferae), whichinclude the major agricultural host attacked by fleabeetle, oil rapeseed or Argentine canola (B. napus) andPolish canola (B. rapa/campestris). Mustard (Brassicaspp.) and crambe (Crambe abyssinica) are also susceptibleto flea beetle attack but not preferred over canola.Other hosts that flea beetles will attack in the gardensetting are cabbage, turnip, cauliflower, kale, Brusselsprouts, horseradish, and radish. Some weeds attackedin the cruciferous group are flixweed, field pennycress,peppergrass, and wild mustard.Figure 7. The new generation of flea beetles feeding onthe green foliage and pods of canola in mid-July until earlySeptember.Crop DamageThe greatest crop loss occurs during the spring whenflea beetle feed on cotyledons and first true leavesduring the first two weeks after emergence. Leaf tissueof the cotyledons die around adult flea beetle feedingsites producing a shot-hole appearance and necrosis(Figure 8). Under severe pressure in North Dakota, fleabeetles have been recorded attacking the growing point(meristem tissue), killing the plant.Adult feeding on young seedlings results in reducedcrop stands and plant growth, delayed maturity, andlower seed yield. When flea beetle populations are largeand warm, sunny, dry, calm conditions favor feeding,fields can be infested quickly and canola seedlings die.Figure 8. Canola seedling damage,pitting caused by flea beetle feeding (top)and undamaged seedling (bottom).4

Stand losses may result in having to reseed the field.Less severe infestations may result in stunted plants,uneven stands and maturation, and harvest problems.When weather conditions are cool, wet, and windy, fleabeetles may creep slowly into the field and concentratefeeding on the field edges. Spring feeding activityoccurs from May through June.During the summer months, the larvae feed on thesecondary root hairs, but only a negligible effect onyield loss or vigor has been observed. The summergeneration of adult flea beetles emerge after mid-Julyand feed on developing pods (Figure 7). Usually theupper or younger pods and later seeded crops are mostimpacted. This feeding damage results in poor seed fill,premature pod drying, shriveled seeds, or pod shattering,and provides an entry point for fungal growthwithin pods in damp weather.IntegratedPest ManagementIn the spring, overwintering flea beetle adultsemerge, locate, feed on, and damage emerging canolaplants. To effectively manage flea beetles and otherpests of canola, producers should use an IntegratedPest Management (IPM) program. An IPM approachuses multiple strategies to control flea beetles,minimizes inputs, conserves the natural enemies ofpests, and reduces the negative impacts of pesticideson the environment. This type of approach is alsothe most economical. Canola fields should bemonitored on a regular basis to determine thelevel of infestation and damage.Monitoring and Field SamplingFlea beetles overwinter as adults and become activeduring early spring. Field monitoring for flea beetleactivity should begin in newly emerged canola fieldsduring May and June when air temperatures reach 57°F(14°C). Commercial, 4x6 in. yellow sticky traps (Figure10) can be used for monitoring population levels, butthey do not indicate the need for control actions. Assessthe canola field for presence of flea beetles and theirfeeding damage during the first 14 days after cropemergence, or until plants have reached the 4-leaf stage.Fields should be checked daily to identify damage as itdevelops and to make timely management decision.Beetles are most active during sunny, warm, calm anddry weather conditions, so avoid monitoring for fleabeetles when conditions are cool, windy, and damp.The amount of defoliation should be used as a guideto determine the need for management action. Injuryoccurs first at the field edges, particularly where ashelterbelt/grassy area borders a field. The beetlesreadily fly when temperatures exceed 64 o F (17.8 o C) andwill move quickly into the field’s interior. To determinethe extent and distribution of damage, start at the fieldmargins and walk into the field, selecting plants atvarious random intervals. Estimate percent defoliationfor each plant selected. The economic threshold for afoliar application is when an average of 25% of thesurface area of cotyledons and first true leaves hasbeen injured (Figure 9) and beetles are present. Ifleaf damage is less than 25% and the crop is activelygrowing, the crop can usually recover. Watch fieldsclosely in hot, dry weather, when flea populationscan rapidly increase.Foliar treatments must be made quickly if damageexceeds 25% defoliation. Under high beetle pressureand feeding damage, a delay of one to two days canresult in loss of entire fields. If damage is limited toonly the edge, spraying only part of the field may25% defoliationFigure 9. Examples of defoliation with25% defoliation on canola cotyledons beingan economic threshold level.5

Figure 10. Yellow sticky trap used formonitoring flea beetle populations.reduce flea beetle numbers. Apply insecticides duringthe sunny, warm part of the day when beetles areactively feeding on the plants. Canola plants that havereached the 4-leaf vegetative growth stage or beyondcan tolerate more feeding damage, unless flea beetlesare damaging the growing point. During years whenflea beetles are abundant through June, a yield lossof about 10% can be common even when the crop isprotected with insecticidal seed treatments. Underthese conditions a later foliar treatment (21 days afterplanting) may be necessary to protect the crop fromre-infestation.The summer generation of adults emerging in lateJuly and August will feed on the leaves, stems, and podsof the maturing crop, but usually does not causeeconomic damage. Control may be necessary in latematuring fields where large and increasing numbersof adults may congregate and feed on green pods.Monitor the summer adult populations in late Julyand August to determine the need for protecting nextyear’s canola crop. If the flea beetle population isabundant in canola swaths,consider a seed treatmentfor the followingproductionseason.EconomicThresholdSeedling:25% defoliation ofcotyledons and firsttrue leaves6

Cultural ControlPlanting DateCanola planted early from April to mid-May reducesthe risk of heat and drought stress during flowering andproduces higher seed yields than canola planted fromlate May to early June. Early seeding with good qualityseed into a shallow, firm seed bed also reduces the riskof feeding injury by flea beetles to canola seedlings.Planting early and shallow helps seedlings emergeearlier, so plants are larger and can tolerate morefeeding by the time flea beetle populations are large.Increased seeding rates may also help reduce flea beetleimpact by reducing overall damage per plant with moreplants per unit area. In Canada, canola planted in widerrow spacings of 7.8-11.8 in. (20-30 cm) resulted indecreased feeding damage per plant than narrower rowspacings of 4 in. (10 cm). Later planted canola may notalways avoid invasion of the flea beetle because ofrepeated migrations into the crop. Flea beetles continueto fly actively throughout May and June. Trap data offlea beetles in the north central region of North Dakotaindicate that flight activity fluctuates throughout Mayand June, perhaps caused by favorable or unfavorableweather conditions.Planting SystemsUse of different cropping systems such as no-till,minimum till, or fall dormant seeding, may offer analternative to the traditional chemical control of fleabeetles on canola. Since flea beetles are more activeduring sunny and warm days, it has been suggested thatthe different cropping systems may provide a lessdesirable, cooler micro-environment for flea beetleactivity. Often, flea beetle populations are lower in notillfields compared to conventional tillage fields.Dormant seeded canola may germinate, emerge, andreach the 4-leaf stage before significant numbers of fleabeetles emerge from overwintering sites. Only 4% ofthe dormant-seeded fields in the north central region ofNorth Dakota during 1999-2000 were sprayed with afoliar insecticide for flea beetle control, compared to25% of the spring-seeded fields, according to a canolagrower survey.Crop RotationSince flea beetles are strong flyers and disperse overwide areas from overwintering sites, crop rotation is notan effective means of managing flea beetles. However,crop rotation is very important in reducing the level ofcanola diseases like blackleg and sclerotinia.Plant ResistanceAlthough some of the larger-seeded varieties are moreresistant to flea beetle damage due to their largeseedling size, no canola varieties exhibit sufficientresistance to protect against flea beetle feeding damage.Biological ControlPredators known to feed on flea beetles include lacewinglarvae (Chrysopa carnea), big-eyed bugs (Geocorisbullatus), the two-lined collops (Collops vittatus), thewestern damsel bug (Nabis alternatus) and the northernfield cricket (Gryllus pennsylvanicus). Parasitic wasps,like Microtonus vittate, are known to attack cruciferflea beetles, but the rate of parasitization is very low.Unfortunately, flea beetle populations emerge duringa narrow window in the spring, and natural enemiesusually do not have enough time to negatively impactflea beetle populations.Insecticide ControlWhen flea beetle populations are large the previous fall,a seed treatment with a systemic insecticide should beapplied as a preventive tactic. About 60-70% of canolaseed in North Dakota is treated with an insecticidefungicide.Treatments provide protection against fleabeetles for about seven-14 days after seedling emergence.Flea beetles can still reduce yield of canolagrown from treated seed by 8-10% when beetle populationsare large and canola is past the protection period.Foliar applied insecticides are effective when beetlepopulations have reached an economic threshold leveland treatments are timed properly. Insecticides registeredfor flea beetle management in North Dakota as of2002 are listed in the table below. Please check with thecurrent Field Crop Insect Management Guide forupdated insecticide registrations. Insecticide users mustREAD, UNDERSTAND, and FOLLOW ALL LABELDIRECTIONS.7

Registered Flea Beetle InsecticidesDosage in ProductInsecticide Lb Ai/acre Per Acre Restrictions on UseCapture 2 EC 0.033 to 0.04 1.3 to 2.6 fl oz Reduced rate is issued as a state 2 (ee) label. Apply in aRUPminimum of 2 gals. of finished spray per acre by air or in aminimum of 10 gals. per acre by ground. When applying by air,1 to 2 quarts of emulsified oil may be substituted for 1 to2 qts of water in the finished spray. Do not apply within 35 daysof harvest.Ethyl-methyl 0.5 0.66 pt Aerial application only, using a minimum of 3 gallons of waterparathion 6-3per acre. Do not apply within 28 days of harvest. Do not enterRUPtreated fields for 3 days after application. Fields must be posted.Gaucho 10.7 - 21.3 oz For use in commercial seed treaters only. Not for use inper hundred- hopper-box, slurry-box or other seed treatment applications at,weight of seed or immediately before, planting.thiamethoxam 23 fl oz per For use in commercial seed treaters only. Contains 3 fungicidesHelix (10.3% active) hundredweight to protect against diseases. There is a 30 day plant backHelix Xtra (20.7% active) of seed restriction.Methyl 0.5 0.5 pt Aerial application only, using a minimum of 3 gallons water perparathion 8ECacre. Do not apply within 25 days of harvest. Do not enterRUPtreated fields within 48 hours after application. Fields must beposted.RUP - Restricted use pesticideAdditional SourcesCanola Connection, Canola Council of Canada,http://www.canola_council.org/Canola Production, NDSU Ext. Service CircularA-686, 1998, http://www.ext.nodak.edu/extpubs/plantsci/crops/a686w.htmNorthern Canola Growers Association,http://www.northerncanola.com/default.asp2002 Field Crop Insect Management Recommendations,NDSU Ext. Service,Circular E-1143, http://www.ext.nodak.edu/extpubs/plantsci/pests/e1143w1.htmPhotograph creditsFigures 1 and 2 were taken by Gerald Fauske,NDSU Department of Entomology.Figures 3, 4, 5 and 6 are used by permission ofSyngenta Crop Protection, Inc.Figures 7, 8, 9 and 10 were taken by Janet Knodel.For more information on this and other topics, see: www.ag.ndsu.nodak.eduNDSU 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, orsexual orientation; and are an equal opportunity employer.2M-9-02This publication will be made available in alternative format upon request to people with disabilities (701) 231-7881.