Compendium of Sunflower Diseases and Pests

Compendium of

Sunflower Diseases and Pests

Part II. Insect Pests Head Feeders Banded Sunflower Moth The banded sunflower moth (Cochylis hospes) is found on sunflowers from Manitoba (Canada) south to Texas and east to New Jersey and North Carolina (U.S.A.). In the northern part of its range, it is a serious pest of sunflower.

Injury Larvae feed on florets and developing seeds, interfering with pollination and reducing the number of seeds per head. As a result of larval feeding, yield and oil content are lowered. An older larva will chew a hole in the top of the seed and then feed inside it, consuming the entire kernel. Each larva can damage six to seven seeds. Symptoms of larval feeding include areas of silk webbing on the faces of the sunflower heads. Larvae typically exit seeds before harvest and generally do not cause heating and moisture problems in storage.

Identification The adult C. hospes moth is small, about 6 mm long, and has tan wings with a dark-­brown triangle in the middle of the forewing (Fig. 189). Another Cochylis species, C. arthuri, feeds on sunflower and causes similar seed damage; however, it is not as abundant as the banded sunflower moth.

Eggs are about 0.5 mm long and 0.3 mm wide and oblong.

They change color from white to light brown as they mature (Fig. 190).

Larvae vary in color depending on maturity: pink to white for early instars and green to red for late instars. Larvae range

Fig. 189. Banded sunflower moth adult (Cochylis hospes). (Cour­tesy P. Beauzay—© APS)

in length from 1.6 mm for newly hatched larvae to 12.7 mm for mature larvae (Fig. 191). All stages have a dark-­brown head capsule.

Mature larvae form silk puparia in the soil prior to pupation.

Biology and Life Cycle The banded sunflower moth produces one generation per year in the northern Great Plains; however, there can be more than one per year in the southern regions. The adult moth has a wide emergence window, first appearing in July and continuing for 8 weeks, usually through August. Adult longevity is about 7–10 days. Adult moths typically rest in the vegetation (for example, broadleaf weeds in ditches) surrounding a sunflower field during the day. Females move into the field to lay eggs during the evening. Females prefer to oviposit on midsized buds in the R-3 crop stage. After pollen shed (R-5.1), sunflowers are no longer susceptible to egg-­laying activity. Female moths deposit eggs singly or in small clusters on the outer whorls of bracts. Eggs hatch in 5–8 days.

Larvae develop through five instars, which takes about 10–14 days to complete. Young larvae feed on the bracts and later move to the disk flowers to feed on pollen. After the third instar, larvae tunnel through the disk flowers and into young, developing seeds. Several seeds are consumed by each larva.

Mature larvae drop to the ground and form silk cocoons in the soil for overwintering. Pupation occurs the following year in June and July and lasts about 12 days.

Fig. 190. Banded sunflower moth eggs (Cochylis hospes). (Photo

by K. Mundal. Reproduced, with permission of North Dakota State University Extension Service, from NDSU Extension Publication E823 (revised), Banded Sunflower Moth)

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Management Delaying planting to late May or early June reduces infestation levels of and damage by the banded sunflower moth. However, producers should consider how planting sunflowers late affects yield. Deep fall plowing can reduce spring emergence of the banded sunflower moth by up to 80%, but deep plowing is no longer recommended because of soil conservation practices.

Resistance to the banded sunflower moth has been evaluated and identified in selected sunflower accession lines and sunflower hybrids.

Pheromone lures and traps are available for monitoring (Fig. 192). However, traps do not indicate treatment thresholds and should be used only for determining emergence and population levels in fields. Scouting for eggs or adult moths is necessary to determine if fields require an insecticide treatment.

(Producers should refer to NDSU Extension Service Bulletin E823 for egg and adult moth scouting protocols and formulas for egg and adult moth thresholds; see Knodel and Charlet, 2010, in the Selected References.) The optimal insecticide application timing is when larvae have just hatched and are beginning to feed on disk flowers, which usually occurs near the R-5.1 growth stage (beginning of pollen shed). Producers should consult their local extension offices for information about insecticides registered in sunflower for control of the banded sunflower moth.

Selected References Arthur, A. P., and Powell, Y. M. 1990. Description of the last-­instar of Cochylis arthuri Dang (Lepidoptera: Cochylidae) and characters for separating it from last-­instar larva of Cochylis hospes Walsingham. Can. Entomol. 122:627-­631.

Chirumamilla, A., Knodel, J. J., Charlet, L. D., Hulke, R. S., Foster, S. P., and Ode, P. J. 2014. Ovipositional preference and larval performance of the banded sunflower moth (Lepidoptera: Tortricidae) and its larval parasitoids on resistant and susceptible lines of sunflower (Asterales: Asteraceae). Environ. Entomol.

43:58-­68.

Knodel, J. J., and Charlet, L. D. 2007. Pest management—Insects.

Pages 26-­53 in: Sunflower Production. D. R. Berglund, ed. North Dakota State University Ext. Serv. Bull. A1331.

Knodel, J. J., and Charlet, L. D. 2010. Banded Sunflower Moth. North Dakota State University Ext. Serv. Bull. E823 (rev.).

Oseto, C. Y., Charlet, L. D., and Busacca, J. D. 1989. Effects of planting date on damage caused by the banded sunflower moth (Lepidoptera: Cochylidae) in the northern Great Plains. J. Econ. Entomol.

82:910-­912.

(Prepared by J. D. Bradshaw, J. R. Prasifka, J. J. Knodel, and J. P. Michaud)

Sunflower Bud Moth The sunflower bud moth (Suleima helianthana) is a small moth in the family Tortricidae. It does not typically cause economic damage in sunflower; however, the adult moth can look similar to other more damaging moths (for example, the banded sunflower moth). Because this insect rarely causes economic damage to sunflower, no sampling plans or economic thresholds have been developed.

Injury

Fig. 191. Banded sunflower moth larvae (Cochylis hospes).

(Reproduced by permission of North Dakota State University Extension Service)

Injury to sunflower from the sunflower bud moth differs depending on the generation. The larvae of the first generation typically bore into sunflower stems near the bases of leaf petioles. This stem-­feeding behavior results in the extrusion of plant sap and insect feces (frass) through the openings left by the larvae. This injury is not associated with economic damage to the plant. However, second-­generation larvae typically enter the axial sides of sunflower receptacles and feed on the pith and developing achenes. Economic damage occurs when larvae retard the development of sunflower ovules above the burrowing points. This activity creates areas of the sunflower head without floret material: “bald spots.”

Identification The adult sunflower bud moth is gray-­brown and has two dark, transverse bands across the forewings (1.6-­ cm wingspread) (Fig. 193). The larva is cream-­colored and has a dark head capsule; it reaches 0.8–1.1 cm at last instar (Fig. 194).

The wings of the adult (as with all Tortricidae) are folded over the body at rest. However, the sunflower bud moth can be distinguished from other pest tortricid moths by the two dark, transverse bands on the forewings.

Biology and Life Cycle

Fig. 192. Pheromone trap for the banded sunflower moth (Cochylis hospes). (Reproduced by permission of North Dakota State University Extension Service)

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Sunflower bud moths produce two generations per year.

They overwinter as pupae within sunflower residue; then, in the spring, the adults emerge, mate, and deposit eggs, primarily on the terminals of vegetative sunflowers. Once the eggs hatch, these first-­generation larvae bore into sunflower stems near the bases of leaf petioles to feed and develop within the stems. Mature larvae move back to the same openings to pupate, which ultimately facilitates the moths’ exit. The resulting second-­ generation moths prefer to lay eggs on the receptacles of reproductive sunflowers. These second-­generation larvae bore into

Fig. 193. Sunflower bud moth adult (Suleima helianthana). (Reproduced with permission of Mark Dreiling, from Bugwood.org).

Fig. 194. Sunflower bud moth larva (Suleima helianthana). (Reproduced with permission of Frank Peairs, Colorado State University, from Bugwood.org)

the axial sides of sunflower receptacles. The larvae develop within the receptacles and return to their entrance holes to pupate and overwinter.

Management No economic thresholds are available for this insect. Because the larvae are protected within the sunflower, insecticides will not likely come into contact with them; therefore, chemical controls are not recommended.

Selected Reference Pilson, D. 2000. Herbivory and natural selection on flowering phenology in wild sunflower, Helianthus annuus. Oecologia 122:72-­82.

(Prepared by J. D. Bradshaw, J. R. Prasifka, J. J. Knodel, and J. P. Michaud)

Headclipping Weevil The headclipping weevil (Haplorhynchites aeneus) is a species indigenous to North America that attacks a wide range of composite flowers, both wild and cultivated. It is widely distributed east of the Rocky Mountains (U.S.A.) and can be problematic in outdoor nurseries where ornamental composite flowers are produced. This weevil seems to find the large blooms of

Fig. 195. Damage to three successive sunflower plants caused by the headclipping weevil (Haplorhynchites aeneus). (Cour ­tesy R. M. Harveson—© APS).

Fig. 196. Headclipping weevil adult (Haplorhynchites aeneus).

(Cour­tesy J. P. Michaud—© APS)

commercial sunflowers especially attractive. Adult beetles can be observed on flowers, often in the act of mating or cutting flower stems. The beetles may also sever leaf petioles if they enter fields before flower buds have emerged. Little research or control information is available on this pest because of its minor significance.

Injury The damage caused by the headclipping weevil can be alarming to growers (Fig. 195), but it rarely justifies control measures in commercial sunflower fields. Damage is typically concentrated along field edges where it is highly visible, so any effort to assess the extent of the problem should involve walking a transect through the center of the field. Notably, wild sunflowers readily compensate for clipped flowers by producing additional buds that flower later and sustain lower levels of overall seed damage; this compensatory response is not an option for monocephalic cultivated varieties.

Identification The headclipping weevil is shiny, black, and about 1.3 cm long with soft wing covers and a gently curved proboscis that is about half as long as the body (Fig. 196). Adults are often covered with a coating of pollen, which is their primary food.

Eggs are laid in clipped heads, which are the most recognizable evidence of weevil activity. Larvae are legless grubs but can be difficult to find within the heads.

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Biology and Life Cycle

Injury

Headclipping weevils produce a single generation per year; the adults emerge from the soil in midsummer. Female weevils cut the peduncles of flowers, which usually remain dangling from stalks for some time. Aggregations of mating adults can often be found clustered within clipped flower heads, especially those clipped before they are fully open. Larvae first feed on pollen and florets within the flower and then complete their development by feeding on decomposing ovules after the heads fall to the ground. Mature larvae then leave the heads to excavate chambers in the soil, where they overwinter; they pupate and emerge as adults the following summer.

Adult sunflower midges do not damage sunflower plants.

Early larval feeding under the involucral bracts produces visible necrosis on and around bracts (Fig. 197). As larvae grow, they move toward the centers of the heads. Feeding by small numbers of second and third instars at the bases of achenes may cause abortion of a few seeds. However, large numbers of midge larvae feeding in the heads is thought to elevate levels of auxins, producing heads that are heavily concave or “cupped” and have little or no seed (Fig. 198). Although little damage has been observed since 2005, severe infestations reportedly have caused some farmers to abandon sunflower production.

It is impractical to estimate the numbers of larvae present in infested heads (and some larvae may be gone once symptoms are noted). Thus, assessment of damage caused by the sunflower midge typically relies on rating scales for damage to the bracts and head deformity, which correlate well with per-­plant yield reductions.

Management Treatment may be justified if 5% or more of flower heads are clipped and weevils are still active in the field. No insecticides are registered for this pest, but those targeting sunflower seed weevils should also be effective against headclipping weevils. Treatments that target the sunflower moth usually kill most headclipping weevils. Removal and destruction of clipped flower heads is often recommended for reducing populations in ornamental flower nurseries but is not practical in commercial sunflower fields.

Selected References Hamilton, R. W. 1981. Description of the larva and pupa of Haplorhynchites aeneus (Coleoptera: Curculionoidea, Rhynchitidae).

J. Kansas Entomol. Soc. 54:616-­624.

Pilson, D., and Decker, K. L. 2002. Compensation for herbivory in wild sunflower: Response to simulated damage by the head-­clipping weevil. Ecology 83:3097-­3107.

Identification Because adult sunflower midges are small (2–3 mm) and short-­lived, they are rarely seen. The minute, yellow eggs, which are often laid in clusters near the involucral bracts or in the centers of bud-­stage sunflowers, are also not easily detected.

Sunflower midge larvae (Fig. 199) found beneath the bracts or feeding among the immature achenes are mostly nondescript

(Prepared by J. D. Bradshaw, J. R. Prasifka, J. J. Knodel, and J. P. Michaud)

Sunflower Midge Although several midge species infest sunflowers, the sunflower midge (Contarinia schulzi) is by far the most significant pest. The sunflower midge may be found in sunflower-­growing areas from Texas (U.S.A.) to Canada, but its economic importance is largely confined to Minnesota and North Dakota (U.S.A.) and to Manitoba (Canada). After the eggs laid by this minute fly hatch, larval feeding on sunflower heads can cause mild to extreme deformities, in some cases resulting in a complete yield loss for infested plants.

Fig. 197. Damage to the sunflower head caused by a sunflower midge larva (Contarinia schulzi). (Cour­tesy T. J. Gulya)

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Fig. 198. Cupped head caused by feeding of the sunflower midge (Contarinia schulzi). (Cour­tesy T. J. Gulya)

Fig. 199. Sunflower midge larva (Contarinia schulzi). (Cour­tesy P. Beauzay—© APS)

fly larvae (light and translucent, legless, with darkened mouthparts visible within the anterior end). A tentative identification of sunflower midge larvae may be supported by an unusual behavior, in which larvae appear to jump when disturbed. However, unless fields are being closely monitored, identification (and severity) of sunflower midge infestation is generally determined by the presence of symptoms. The loss of ray florets may be a relatively early indication of midge feeding, although symptoms on the bracts and heads are more commonly noted.

Biology and Life Cycle Sunflower midge can have two or more generations per year.

In North Dakota, adult emergence begins in June. Adults prefer to lay eggs in buds, particularly for sunflowers whose bracts do not conceal the center of the developing capitulum. However, midge females may lay eggs in leaf axils if sunflowers at the preferred stages of maturity are not available. Adults live only 2–3 days, and larvae complete development in 2 weeks or less. When larvae are mature, they drop to the soil and either overwinter as larvae or pupate to begin another generation, depending on environmental conditions. Sunflower midges are known to infest several species of sunflower, but they appear to be restricted to Helianthus spp.

Management Insecticides are difficult to use for the sunflower midge because its lifespan is short and its larvae are protected under plant tissue. Late planting can sometimes reduce damage by lowering the risk or severity of infestation. Sunflowers with a closed bud morphology receive fewer midge eggs. Hybrids with resistance have also been used, but recently injury by sunflower midge has been too inconsistent to reliably evaluate germplasm.

infestation, even though larval survival is much lower in wild Helianthus annuus flowers.

Monocephalic commercial sunflowers provide a concentrated food supply for larvae and simultaneously a refuge from many generalist parasitoids of Lepidoptera that are unable to access larvae in the large blooms. Furthermore, large synchronous monocultures of sunflowers reward the hordes of migratory moths able to colonize fields precisely when plants are approaching the reproductive stage. Since the 1980s, as commercial production has expanded, sunflower moth problems have intensified throughout the central Great Plains.

Injury Sunflowers are susceptible to sunflower moth damage from stage R-5.1 (onset of anthesis) to R-6 (petals drying), although the moth prefers flowers in the early stages of bloom for oviposition. Larval feeding damage creates points of entry for Rhizopus spp., the facultatively pathogenic fungus that causes sunflower head rot. Rhizopus head rot is usually the primary cause of yield loss, not seed consumption by larvae. Multiple infections early in flower development are often sufficient to cause complete loss of the flower head (Fig. 200), whereas later infections can invade vascular tissues of the peduncle, reducing seed set and oil content. A combination of heavy moth pressure and humid conditions (ideal for fungal growth) can easily result in complete yield loss if the larvae are not controlled before they bore into the flower heads.

Identification The adult sunflower moth is 1.5–2.0 cm long, slender, and whitish to pale gray (Fig. 201). Larvae are active at night and leave mats of webbing on the flower faces, which are indicative of infested heads. Larvae are distinctive in appearance, bearing

Selected References Anderson, M. D., and Brewer, G. J. 1991. Mechanisms of hybrid sunflower resistance to the sunflower midge (Diptera: Cecidomyiidae).

J. Econ. Entomol. 84:1060-­1067.

Anderson, M. D., and Brewer, G. J. 1992. Sensitivity to 2,4-­D in sunflower as an indicator of tolerance to the sunflower midge (Diptera: Cecidomyiidae). J. Econ. Entomol. 85:299-­303.

Rogers, C. E., Thompson, T. E., and Gagne, R. J. 1979. Cecidomyiidae of Helianthus: Taxonomy, hosts and distribution. Ann. Entomol.

Soc. Am. 72:109-­113.

Schulz, J. 1973. Damage to cultivated sunflower by Contarinia schulzi.

J. Econ. Entomol. 66:282.

(Prepared by J. D. Bradshaw, J. R. Prasifka, J. J. Knodel, and J. P. Michaud)

Fig. 200. Severe head rot caused by a Rhizopus sp. The pathogen often enters the head via feeding sites of the sunflower head moth (Homoeosoma electellum). (Cour­tesy S. M. Thompson—© APS).

Sunflower Head Moth The sunflower moth (Homoeosoma electellum) is indigenous throughout subtropical North America, where it infests the developing flower heads of a variety of composite plants (Asteraceae). Populations east of the Rocky Mountains appear to be distinct from those in California (U.S.A.), and they express strong migratory tendencies, which contributes to their evolution as key pests of commercial sunflower on the High Plains. Breeding year-­round in southern Texas (U.S.A.) and northern Mexico, they exploit seasonal weather systems to migrate northward as far as the Canadian prairies.

Each migration is comprised of a succession of generations, and the number of moths sometimes increases during its course by several orders of magnitude. For example, infestations of commercial sunflower in Texas typically range from five to 15 larvae per head, whereas two generations later in Kansas, the average is often 200 larvae per head. In years when wild sunflowers are abundant, they may become a secondary source of

Fig. 201. Sunflower head moth adult (Homoeosoma electellum).

(Cour­tesy J. P. Michaud—© APS)

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brown and white longitudinal lines and orange-­brown head capsules (Fig. 202).

Biology and Life Cycle Sunflower pollen is an oviposition stimulus for female moths.

A female can lay up to 400 eggs, usually placing each egg at the base of a floret. Larvae feed almost exclusively on pollen during the first two instars, and later they burrow into receptacles, chewing through the pith and developing achenes. Depending on temperature, larvae will feed for 2–3 weeks and then descend to the ground on silken threads to pupate in the soil. A generation can be completed in 30 days in warm weather. The largely nocturnal adults are strong fliers, and once above the boundary air layer, they can ride strong wind currents (low-­ level jets) for hundreds of miles in a single night.

Although capable of diapause and of overwintering in Texas, the sunflower moth is not known to overwinter in significant numbers further north. Rather, as autumn approaches, the emerging moths respond to lower temperatures and shorter days by attempting a return journey south, taking advantage of transient southerly air flows that typically form behind advancing cold fronts.

Management Successful management of the sunflower moth hinges on vigilant monitoring of the crop throughout the flowering period, followed by prompt treatment when threshold numbers of moths are present. Every field has a unique phenology and should be scouted independently. Scouting can begin at the R-4 stage, because large flights of moths may enter fields prior to bloom, but it should not be delayed beyond R-5.1. The most accurate counts are obtained by scouting with a flashlight about 1 h after sunset, when moth activity peaks. Scouts should count the number of moths on the faces of at least 20 flowers at each of five locations in a field. The treatment threshold should be one to two moths per five flowers, depending on the crop condition and anticipated market value.

Treatment is best applied from a ground rig using a large volume of water (190–238 L/ha) to maximize coverage. Aerial application may be more convenient for the farmer but will deliver material in much lower volumes (typically 9.5 L/ha) and will be more susceptible to wind and drift. Coverage can be improved by flyovers from an eastern orientation that direct spray droplets onto flower faces. Generally, contact insecticides are the most effective, because they target adult moths before they lay eggs. However, larvae remain vulnerable until the end of the second instar because of their pollen-­feeding behavior. Another good choice may be the diamide insecticides, which have some

systemic activity and have demonstrated efficacy with an initial application at 1% bloom followed by a second application 7–10 days later.

Because eggs may be laid until R-6, more than one application may be required when moth pressure is heavy, regardless of the material selected. Scouting should be repeated every 2–3 days until the ray petals have dried. The earlier a contact insecticide is applied, the higher the chance a follow-­up treatment will be needed, because flowers not fully expanded will outgrow the protection.

By repeatedly scouting, as opposed to simply spraying when flowers open, farmers can possibly avoid treatments and reduce production costs. Although commercial sunflowers are self-­ compatible, cross-­pollination increases seed set and oil content, so insecticide applications can cause a small yield loss because of pollinator mortality or avoidance. Preliminary studies suggest that diamides may be more selective than other pesticides, killing crop-­feeding insects but not pollinators. Pheromone traps can be used to monitor moth activity but are cumbersome to install and give variable results. Commercial pheromone lures for this species give mixed results. Strong winds can lead to passive catching of other moth species, and intermediate catch rates mandate visual scouting, all of which largely negate any practical advantage of trapping.

Selected References Beregovoy, V. H. 1985. Appearance of first generation larvae of the sunflower moth, Homoeosoma electellum (Hulst) (Lepidoptera: Pyralidae) in the central United States. J. Kan. Entomol. Soc. 58:739-­742.

Chen, Y. H., and Welter, S. C. 2007. Crop domestication creates a refuge from parasitism for a native moth. J. Appl. Ecol. 44:238-­245.

Delisle, J., McNeil, J. N., Underhill, E. W., and Barton, D. 1989. Helianthus annuus pollen, an ovipositional stimulant for the sunflower moth, Homoeosoma electellum. Entomol. Exp. Appl. 50:53-­60.

Michaud, J. P. 2011. Challenges to effective management of sunflower insects on the High Plains. Pages 169-­182 in: Sunflowers: Cultivation, Nutrition and Biodiesel Uses. V. C. Hughes, ed. Nova Science, New York.

Riemann, J. G. 1986. Reproductive potential and other aspects of the biology of the sunflower moth, Homoeosoma electellum (Hulst) (Lepidoptera: Pyralidae). J. Kan. Entomol. Soc. 59:32-­36.

Rogers, C. E. 1978. Sunflower moth: Feeding behavior of the larva.

Environ. Entomol. 7:763-­765.

Rogers, C. E., Stafford, R. E., and Zimmer, D. E. 1976. Predisposition of sunflower to Rhizopus head rot by the sunflower moth. Texas Agric. Exp. Stn. Prog. Rep. PR-­3422.

Rogers, C. E., Thompson, T. E., and Zimmer, D. E. 1978. Rhizopus head rot of sunflower: Etiology and severity in the southern plains.

Plant Dis. Rep. 62:769-­771.

Teetes, G. L., and Randolph, N. M. 1970. Hibernation, spring emergence, and pupation habits of the sunflower moth, Homoeosoma electellum. Ann. Entomol. Soc. Am. 63:1473-­1475.

Thompson, T. E., Rogers, C. E., and Zimmerman, D. C. 1980. Sunflower oil quality as affected by Rhizopus head rot. J. Am. Oil Chem.

Soc. 57:106-­108.

(Prepared by J. D. Bradshaw, J. R. Prasifka, J. J. Knodel, and J. P. Michaud)

Sunflower Receptacle Maggot

Fig. 202. Sunflower head moth larvae (Homoeosoma electellum).

(Cour­tesy J. P. Michaud—© APS)

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The sunflower receptacle maggot (Gymnocarena diffusa) is distributed primarily in the U.S. Great Plains, ranging from Montana south to Arizona and east to Missouri. This insect is not considered a major pest, because it does not feed on the seeds of cultivated sunflowers. Feeding injury is caused by larvae tunneling in the receptacles of sunflower heads. As a result, field sampling protocols and pest management strategies have not been developed for the sunflower receptacle maggot.

Injury Injury by the sunflower receptacle maggot is caused by larvae feeding on the spongy receptacle tissue of sunflower heads.

If feeding injury is severe, the heads may become partially deformed. This insect pest is not considered to be economically important, because damage to the heads is insignificant and no major field incidences have been reported since 2010.

the eggs hatch, the larvae tunnel into the spongy tissue of the receptacles, where they feed for about 20–30 days. As larvae mature, they may tunnel down into the petioles. From August through September, most chew holes in the backs of sunflower heads and drop to the soil to pupate, although some pupate in the receptacles of sunflower heads. They over­ winter as pupae.

Identification

Management

The sunflower receptacle maggot is the largest of the three tephritid flies that feed on sunflowers. Adults are about 7.6–7.8 mm long and have bright-­green eyes. Their wings are yellowish-­ brown and patterned with darker, transverse, hyaline bands that extend to the posterior margins (Fig. 203). The wingspan is approximately 19 mm. Eggs are white and become brown as they mature. Larvae are white to cream and about 7.8 mm long at maturity (Fig. 204). Pupae are barrel-­shaped and brown.

No field scouting protocol has been developed for the sunflower receptacle maggot. The following natural enemies have been observed: a parasitoid, Perilampus sp., from a pupa; an Aspergillus sp. from an infected pupa; and an unidentified mite from an adult. No economic injury level or economic threshold has been developed for this insect, because it is not considered an economically significant pest. Insecticide use is not warranted for its control.

Biology and Life Cycle The sunflower receptacle maggot produces one generation per year. Adults emerge from late June to early July, around the same time that wild Helianthus spp. form buds. Adult flies are attracted to and feed on the extrafloral nectary secretions of native Helianthus buds. Flies are attracted to cultivated sunflower buds, which are 5–10 cm in diameter.

The female requires a preoviposition period of about 15–20 days before egg laying. Eggs are laid between the second and fourth layers of bracts of developing sunflower heads. After

Selected References Kamali, K. 1973. Biology and ecology of the tephritid complex on sunflower (Diptera: Tephritidae). Ph.D. diss. North Dakota State University, Fargo.

Kamali, K., and Schulz, J. T. 1973. Characteristics of immature stages of Gymnocarena diffusa (Diptera: Tephritidae). Ann. Entomol. Soc. Am. 66:288-­291.

Kamali, K., and Schulz, J. T. 1974. Biology and ecology of Gymnocarena diffusa (Diptera: Tephritidae) on sunflower in North Dakota. Ann. Entomol. Soc. Am. 67:698-­699.

Knodel, J. J., Charlet, L. D., and Gavloski, J. 2010. Integrated Pest Management of Sunflower Insect Pests in the Northern Great Plains. North Dakota State University Ext. Serv. E1457.

(Prepared by J. D. Bradshaw, J. R. Prasifka, J. J. Knodel, and J. P. Michaud)

Sunflower Seed Maggot

Fig. 203. Sunflower receptacle maggot adult (Gymnocarena dif­ fusa). (Cour­tesy J. D. Bradshaw—© APS)

The sunflower seed maggot (Neotephritis finalis) is common in North America and is distributed from southern Alberta to Manitoba (Canada), south to Virginia and Georgia and west to California (U.S.A.), and into northern Mexico. Based on an annual sunflower survey and complaints from seed companies, it caused significant damage to sunflower heads in localized areas of North Dakota from 2008 to 2010. The adult fly is long-­lived and common in sunflowers at any crop stage. Larvae damage the sunflower heads by tunneling through the developing florets and seeds, which causes deformed heads and reduced seed yields. There is no standard scouting protocol; however, some pest management strategies have been evaluated.

Injury The sunflower seed maggot infests the heads of Asteraceae plants, including wild and cultivated sunflowers. On developing sunflower buds and young heads, seed sterility is caused by larvae tunneling through the florets. A single mature larva can destroy about 12 florets. On older sunflower heads, each larva typically damages one to three seeds. A symptom of feeding injury is a line or crease on the face of the sunflower head (Fig. 205). The degree of damage depends on maggot density and the crop stage infested. When damage is severe, the head is strongly deformed and the seed yield is reduced.

Identification Fig. 204. Sunflower receptacle maggot larva (Gymnocarena dif­ fusa). (Reproduced with permission of Frank Peairs, Colorado State University, from Bugwood.org)

The sunflower seed maggot is the smallest of the three tephritid species that attack sunflower. Adults have a body length of about 6 mm and a wingspan of 7 mm. The wings have a brown, lacelike appearance (Fig. 206). Eggs are about 1.2 mm long, white, and elongated and have a nipplelike projection at the dis91

tal end (Fig. 207). Larvae are white to cream, headless, legless, and about 4.5 mm long at maturity (Fig. 208). Pupae are barrel-­ shaped, brown, and about 4 mm long (Fig. 209).

Biology and Life Cycle Sunflower seed maggots are multivoltine; however, in the northern Great Plains, they only produce two generations per year. Adult flies are present during any sunflower crop stage and can be observed resting or mating on sunflower foliage or heads during the day. Adult longevity ranges from 64 to 87 days, with an average of 78 days.

Females lay eggs singly or in groups of four to five between the disk flowers on sunflower heads. In the laboratory, female flies have an average preoviposition period of 19 days. Females oviposit for about 20 days and produce 20–30 eggs. Eggs hatch in 4 days. Larvae develop through three larval instars over 14–16 days. Larvae of the first generation pupate in developing sunflower heads. The small, brown pupae can be observed easily in the faces (Fig. 209). Pupae mature into the next generation of adult flies in 8–9 days. The complete life cycle, from egg to adult, is approximately 26–29 days.

Adult flies of the second generation are most active on late-­ blooming sunflower fields in August. Adult flies overwinter in tree shelterbelt areas and emerge the next summer.

Management Late planting (early to mid-­June) is more effective in reducing the amount of damage and the incidence of damaged heads than early planting (mid-­to late May). Two parasitoids that attack the larval or pupal stages of sunflower seed maggot are

Fig. 207. Sunflower seed maggot eggs (Neotephritis finalis). (Cour­ tesy P. Beauzay—© APS)

Fig. 205. Feeding damage caused by the sunflower seed maggot (Neotephritis finalis). (Reproduced by permission of North Dakota State University Extension Service)

Fig. 206. Sunflower seed maggot adult (Neo­ tephritis finalis). (Cour­tesy P. Beauzay—© APS)

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Fig. 208. Sunflower seed maggot larva (Neotephritis finalis).

(Reproduced by permission of North Dakota State University Extension Service)

Fig. 209. Sunflower seed maggot pupa (Neotephritis finalis). (Cour­ tesy P. Beauzay—© APS)