Published 1997 5 Sunflower Insects LAURENCE D. CHARLET USDA-ARS Northern Crop Science Laboratory Fargo, North Dakota GARY J. BREWER North Dakota State University Fargo, North Dakota BERNARD A. FRANZMANN Queensland Department ofPrimary Industries Toowoomba 4350 Australia A diverse assemblage of insect species attack sunflower (Helianthus annuus L.) worldwide (Rajamohan, 1976; Rogers, 1992). Since sunflower is native to North America, a large pest complex has evolved on wild sunflower and has moved from wild ancestors to commercial cultivars. In other countries and to a lesser extent in North America, some insects have adapted to utilize sunflower as an alternative host. Many of these insects develop or increase in number on adjacent or earlier-planted crops and then after senescence move to sunflower. The successful management of insect pests depends on correctly identify­ ing the pest, understanding the pest's biology, field sampling of pest densities, and selecting the appropriate control methods. The use of integrated pest man­ agement assures that control decisions will be based on economics and achieved with minimal disruption to the environment, the least possible harm to nontarget organisms, and reduced probability that secondary or minor pests will likely become a problem. The integrated pest management philosophy will assure that the most effective control strategies are management techniques that combine resistant cultivars, cultural control, biological control, and the application of insecticides only when pest populations have reached economic injury levels. Insecticides approved for usage on specific insects are constantly changing based on the registration of new products or loss of current registration, therefore the local county agent, crop consultant, or state extension service should be contact­ ed for current recommendations. The discussion of insects associated with sun­ flower that follows is organized by the continent or region in which they occur and by the part ofthe plant attacked (see insert with color plates). Copyright © 1997. American Society of Agronomy. Crop Science Society of America, Soil Science Society of America, 677 S. Segoe Rd., Madison, WI 53711, USA. Sunflower Technology and Produc­ tion, Agronomy Monograph no. 35 . 183 184 CHARLET ET AL. INSECT PESTS OF THE UNITED STATES, CANADA, AND MEXICO Sunflower is utilized by a wide array of insect species, both as a food plant and as a source of pollen and nectar. Over 150 phytophagous insect species have been reported from cultivated and native species of sunflower in North America (Hilgendorf & Goeden, 1981; Rogers, 1988b). Sunflower is the only row crop in North America that coexists with its native congeners. This unique relationship has enhanced development of insect problems by providing monocultures of host plants where only isolated hosts were once available. A number of insect species have adapted to cultivated sunflower and have become consistent economic pests (Charlet et aI., 1987). STEM AND ROOT FEEDING SPECIES Cutworms [Lepidoptera: Noctuidae] Cutwonns are perennial pests of sunflower occurring in isolated outbreaks. In the upper Great Plains of North America, four species are common. These are the dark-sided cutwonn [Euxoa messoria (Harris)], the red-backed cutwonn [E. ochrogaster (Guenee)], the pale western cutwonn (Agrotis orthogonia Morrison), and the dingy cutwonn (Feltia ducens Walker). Other cutwonn species attacking sunflower vary by region (Westdal, 1975). Description Dark-Sided Cutworm. The adult has forewings that are usually light, powdery, and grayish-brown with indistinct markings. Larvae are pale-brown dorsally, white on the ventral areas, and with indistinct stripes on the sides. At maturity, larvae are 25 to 32 mm in length. Red-Backed Cutworm. Forewings of the adult are reddish-brown with characteristic bean-shaped markings. The larvae are dull-gray to brown with soft fleshy bodies and are from 25 to 32 mm in length when grown. Larvae are char­ acterized by two dull-reddish stripes along the dorsal side. Pale Western Cutworm. Forewings on the adult are tan and mottled with light-colored primary wing veins. Hindwings are white, darkening distally. Larvae are grayish in color without spots or stripes, but the body has fine, flat granules. Dingy Cutworm. Adults have forewings with bean-shaped markings sim­ ilar to those found on the red-backed cutworm. The hind wings of males are whitish with a broad, dark margin along the outside while those o( females are unifonn dark gray in color. Larvae are a dull, dingy-brown color with a broad, dull-gray dorsal stripe, which is separated into triangular-shaped areas on each segment. A narrow, dark stripe is on each margin of the central stripe (Capinera & Schaefer, 1983; McBride et aI., 1985, 1994; Metcalf & Metcalf, 1993). SUNFLOWER INSECTS 185 Life History The dark-sided and red-backed cutworms have similar life histories. Larvae of these species emerge in May and early June and develop until about the end of June. Pupation lasts about 3 wk and takes place in the soil in earthen cells near the soil surface. Eggs are oviposited in the soil in late July and early August and remain dormant until the following spring. There is one generation per year. The pale western cutworm feeds underground and usually ceases feeding by late June. Eggs are laid singly or in small groups on the soil and hatch on warm winter days or in early spring. There is a single generation per year. The dingy cutworm is a northern species. They emerge as adults in August and are active until mid-October. Eggs are deposited and hatch in the fall. Dingy larvae develop to the second or third instar before overwintering in the soil. Pupation occurs in the spring to early summer. There is one generation per year (McBride et al., 1985, 1994; Metcalf & Metcalf, 1993). Damage Cutworms damage sunflower by cutting the stem of the plant from 2 to 5 mm above or below the soil line, although occasionally, damage may occur at greater distances from the soil line. Sometimes, larvae, especially the dark-sided, climb the plant to feed on foliage. Larvae are most active at night and hide in the soil during the day. Wilted and dead plants are evidence of cutworm damage. Severed plants wither and may blow away leaving distinct bare patches in the sunflower field. Cutworms have a wide host range and infest most row crops. In sunflower, a gap of 10 to 12 plants in a row is necessary before an economic loss is seen (McBride et al., 1985, 1994). Management Strategies Sampling should begin as soon as sunflower plants emerge and fields should be checked twice weekly until about mid-June. The soil around damaged plants should be inspected for cutworm larvae. Species that feed above the soil line can be controlled with the use of poison-bran baits. For other species, insec­ ticides have to be incorporated into the soil. Several insecticides are registered for cutworm control in the USA and Canada. Cutworms are parasitized by a variety of tachinid and hymenopteran parasitoids and insect predators consume a signif­ icant number of cutworm larvae. Disease and birds also limit cutworm damage (McBride et al., 1985, 1994; Metcalf & Metcalf, 1993). Sunflower Bud Moth, Suleima helianthana (Riley) [Lepidoptera: Tortricidae] The only lepidopterous species of potential economic concern as a stem pest is the sunflower bud moth. The moth is found on sunflower from Mexico to the central USA, occurring in all the sunflower growing areas (Pedraza-Martinez, 1990; Rogers, 1979). 186 CHARLET ET AL. Description Moths have gray to brown forewings with two dark bands and a light patch on the back half of the wing tip (Color Plate 1). The first band runs through the middle of the wing. The second band is located near the wingtip. The wingspan is about 17 mm. Eggs are ovoid and translucent-white in color. Sculpturing on the egg surface gives it a wrinkled appearance. Larvae have smooth, cream-colored bodies with yellow-brown head capsules and are about 15 mm in length at matu­ rity. There are five larval instars. Pupae are found in feeding tunnels near the lar­ val entrance hole into the stem (Ehart, 1974). Life History In the Red River Valley of North Dakota and Minnesota, first-generation adults emerge from late May to mid-June and deposit single eggs on the terminal portion of the plant (Ehart, 1974). Larvae tunnel into the stalk, leaf petiole, or receptacle to feed on the pith. Larval tunnels are usually less than 3 cm in length (Rogers, 1979). At maturity, larvae return to the entrance hole to pupate. Entrance holes are characterized by a protuding, black, sticky frass (Color Plate 2). They can be found in the stalk, leaf petiole, or less commonly, the bud. Second-generation adults appear in late July, oviposit on the sunflower bud or stalk, and are active until mid-August. Larvae of the second generation are more likely to feed in the receptacle of the capitula than the first generation. Larvae plug the entrance hole with frass and other material and burrow into undisturbed pith to overwinter (Ehart, 1974). In Texas, infestations can occur in early May. There are two generations per season in North Dakota and northern Texas and possibly three generations per season in south-central Texas (Phillips, 1972). Host species include wild and commercial H. annuus and 16 other species of Helianthus (Rogers, 1979). Damage Infestations are sporadic but can be heavy at times. Although larval feed­ ing sometimes produces malformed stalks, leaf petioles, and capitula, tunneling in stalks does not normally interfere with stem development. Economic damage is usually restricted to those plants in which infestation occurred in terminals of very small plants or in small capitula. Larvae do not feed on seeds but consume the pithy part of the head (Ehart, 1974; Rogers, 1979).