Bionomics and Management of Rhagoletis 225
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Copyright 1976. All rights reserved BIONOMICS AND -:-6109 MANAGEMENTOFRHAGOLET� E. F. Boller Swiss Federal Research Station for Arboriculture. Horticulture. and Viticulture. CH-8820 W1idenswil. Switzerland R. J Prokopy Prokopy Bio-Experimental Farm. Bailey's Harbor, Wisconsin 542021 INTRODUCTION Characteristics 0/ Rhagoletis The genus Rhagoletis, of the dipteran family Tephritidae, includes some 50 de scribed species and is widely distributed over the Holarctic and Neotropical regions (I, 41, 66, 171, 178). The larvae of all known Rhagoletis feed in the pulp of developing fruit, and several species are important economic pests (191). Occasion ally, a Rhagoletis species may be regarded as potentially beneficial, as when R. a/temata was assessed for release as an agent in the biological control of Rosa rubiginosa. a harmful weed in New Zealand (63). Unlike the multivoltine and largely polyphagous species of the economically by U.S. Department of Agriculture on 12/09/10. For personal use only. important genera Dacus, Anastrepha , and Ceratitis, most Rhago/etis species are univoltine and oligophagous. Some of them (e.g. pomonella, cingulata , fausta , in Annu. Rev. Entomol. 1976.21:223-246. Downloaded from www.annualreviews.org dijferens, lycopersella ) have shifted from their economically unimportant native hosts, and established new races on introduced cultivated plants during the past century. The L iterature Since 1960, various aspects of the biology or control of most North American Rhagoletis species have been reviewed by Christenson & Foote (5 1), Bush (41 --45), Dean & Chapman (59), Bateman (17), and Rivard (169). Comprehensive bibliogra phies have been published on pomonel/a (169) and on cingula ta , indijferens, and IAfter September I, 1975, Dr. Prokopy's address will be Department of Entomology, University of Massachusetts, Amherst, Massachusetts 01002. 223 224 BOLLER & PROKOPY ja us ta (6). No recent bibliography exists for completa, but for ce ras i the European literature up to 1933 has been covered by Thiem (185). A comprehensive bibliogra phy on ce rasi is in preparation (A. Haisch, personal communication). Published studies on Rhagoletis have focused almost exclusively on those species of economic importance. Two species have received the most attention: The North American apple maggot,po monella, which attacks apples and also, in some locali ties, cherries, plums, apricots and pears, and the European cherry fruit fly, cerasi, which attacks sweet and sour cherries. Other economic pests receiving significant but lesser attention include the North American species cingu la ta, indijferens, and fausta , which attack sweet and sour cherries, mendax, which attacks blueberries, completa and sua vis, which attack walnut and in some localities peaches, and bas iola, which attacks rose hips; the European species alfe ma ta , which attacks rose hips; and the South American species Iycopersella, which attacks tomatoes. This review is based in general on the published information on these 11 species. With some notable exceptions, the bulk of investigation on Rhagoletis has re flected the historical development of pest control concepts and has until recently been concerned primarily with control by insecticides and with those aspects of Rhagoletis biology most relevant to achieving such control. Certain aspects of biology vital to the development of integrated control procedures are still poorly understood and will require special attention in the future. In this review, we attempt to provide a balanced discussion of Rhago/etis research principally carried out in Europe and North America. We focus mainly on new knowledge gained during the past decade or so, evaluate this knowledge, and try to point out some existing problems and potential avenues of research. We examine first the biology of individuals, then that of popUlations, and lastly, management. BIOLOGY OF INDIVIDUALS Eclosion Rhagole tis adults emerge from puparia beneath the larval host plant. This process occurs primarily in the morning hours (11, 36, 59, 67, 98), and in basiola is by U.S. Department of Agriculture on 12/09/10. For personal use only. stimulated by rising morning temperatures (11). The flies, which are capable of flight and feeding within two hours of emergence (36, 98,138, 192),evidently spend little Annu. Rev. Entomol. 1976.21:223-246. Downloaded from www.annualreviews.org time on the ground or understory vegetation before leaving (119). Females emerge usually earlier in the year than males, and the sexes reach equilibrium at peak emergence (7,73, 172,180). Pomonella flies from pupae that remai�ed in diapause for two years emerged 1-2 weeks later than the normal population, as did flies from pupae that developed from late apple varieties (7, 137, 142). Synchronization of fly emergence patterns with the ripening pattern of host fruit has been demonstrated in cerasi and proven a valuable aid in differentiating host races (28). Adult Feeding Food is required for gonadal maturation, which in most Rhagoletis species occurs within two weeks of emergence. The flies'search for food is not confinedto the larval BIONOMICS AND MANAGEMENT OF RHAGOLETIS 225 host plant and may carry them to various types of neighboring vegetation (124, i 92). Evidence is accumulating that the principal food source is insect honeydew (34,77, 111, 131; V. Vallo, personal communication) and that probable additional food sources are plant liquids exuding from glandular structures, wounds, and oviposi tion stings (36, 47, 61, 102, 192), numerous bacteria (59), yeasts and fungal spores (36), and insect frass and bird dung. Contact chemoreceptors for food detection have been described in pomonella (l11) and cin gula ta (68). Early workers established that ingestion of water and carbohydrate enhances longevity. But not until Fluke & Allen (65) supplied captive pomon ella flies with yeast was it known that proteinaceous or amino nitrogen was necessary for repro duction. Further definition of the nutritional requirements of adult Rhagoletis (36, 55, 93) eventually led to the development of chemically defined diets for pomonella (34, 128) and completa (189). The knowledge that insect honeydews are usually deficient in certain essential amino acids and probably also in other important nutrients led to the suspicion that the missing nutrients are provided by symbiotes (34, 78) in many fruit .flies (17). Indeed, Pseudomonas me/ophthora, the bacterial symbiote associated with pomo nella (8, 10), has been shown capable of synthesizing 18 amino acids (113) and degrading unsuitable food components, including;nsecticides (35). Symbiotes have received increased attention recently in comp/eta (189), cerasi, a/temata , and meigen i (71, 83). No one has studied the quantity of food required by Rhago/etis for normal fecundity. A paucity of honeydew on vegetation supporting large reproducing Rha go/etis populations has often been observed (59). In view of Fytizas' findingthat one day's exposure of Dacu s oleae females to protein hydrolysate was enough to support a high level of reproductivity over the next 14 days (69), we speculate that the quantity required by Rhagoletis may be less than previously assumed. Dispersal As pointed out by Bateman (17), two types of movement are discernible in adult fruit flies: dispersive and nondispersive movement. The latter is typical of Rha goletis by U.S. Department of Agriculture on 12/09/10. For personal use only. under normal crop conditions; activities associated with feeding, mating, and oviposition rarely take individuals very far from their host plants. Such restricted Annu. Rev. Entomol. 1976.21:223-246. Downloaded from www.annualreviews.org movements have been reported frequently in Rhago/etis species such as comp/eta (15, 36), in differens (67, 90, 143), pomonella (39, 124, 140, 142), and cerasi (30. 195). Dispersive flights have been observed in completa (15), cerasi, (31, 112, 172) and pomonella (108), mostly in situations in which flies were deprived of suitable fruit for oviposition because the crop was destroyed by frost or early harvest. Flight studies in the laboratory with cerasi (168) have shown that flies are capable of flying several kilometers in 24 hr on rotating arms if they are deprived of landing plat forms-distances apparently never flown in nature. These data indicate, however, that natural barriers that provide isolation in genetic control programs, such as forests or open fields without attractive silhouettes, might become less effective in seasons when crop failures induce dispersive movements. 226 BOLLER & PROKOPY Host Detection With approaching sexual maturity, flies move to larval host plants, the site of assembly for mating (41, 43, 158) and oviposition. Mature flies of both sexes accu mulate in greatest numbers on hosts bearing large crops of fruits in prime stage for oviposition (30, 108, 124, 147, 163, 164, 192). Except for recent studies on pomonel/a, the process of host-plant detection by Rhagoletis flies has received scant attention. Foliage color, tree shape, and tree size all play a role in eliciting fly arrival in this species, but none of these cues seem specificto host plants (115). The odor of susceptible host fruit, however, is a specific stimulus that attracts (or arrests) the flies (163). A host-specificleaf stimulus acting as contact arrestant also appears to play a role in host recognition in pomonella (43) and cerasi (E. F. Boller, unpublished data). After arrival on the host plant, the flies detect the fruit solely on the basis of its physical characteristics of shape, contrast-color against the background, and proba bly size (52, 147, 149, 196). Few flights to fruit are made by immature flies (38, 52, 159, 196), or mature flies under conditions unfavorable for mating or oviposition (159). Movement of both mated and unmated Rhagoletis females onto fruit is believed to be motivated primarily by ovipositional drive (4, 36, 161; B. Katsoyan nos, in preparation). Male Rhago ietis establish territories on the fruit and defend them aggressively (4, 36, 38; E. F. Boller, unpublished data) while waiting for females.