TAXONOMIC STATUS, BIOLOGICAL ATTRIBUTES, species, contribute to the difficulty in AND RECOMMENDATIONS FOR FUTURE WORK ON accurately assessing important economic THE GENUS (: ) problems.

By Thomas J. Henry and John D. Lattinl/ ORIGIN OF PEST SPECIES

Species of Lygus, frequently called lygus Pest status varies with the organism and bugs, are the most important agricultural resource being evaluated. Acceptable pests in the plant bug family Miridae population levels may be low when dealing (Heteroptera). The , with disease vectors (Burgess et al., Lygus lineolaris (Palisot), 1983) or much higher when considering occurring over most of North America, is certain defoliators. The pest problem a pest of cotton in the Southern United then is a relative state dependent on the States. In the Western United States, circumstances. Norton and Conway (1977, several species attack and p. 205) provided a useful definition: "A cotton. Because of the severe damage pest problem is, therefore, characterized these plant bugs inflict, an extensive not only by the state of the pest search has been implemented by the U.S. population itself but, more importantly, Department of Agriculture and cooperating as the damage or illness it causes and agencies for natural enemies, especially the value placed on these consequences by nymphal parasites in the family human society." Several Lygus spp. are . This report is an overview considered pests because their feeding of the taxonomic status of the genus damage on certain crops is unacceptable Lygus to help biological control to those involved in crop production researchers better understand the (Graham et al., 1984). This damage often of Lygus and the taxonomic is enhanced because lygus bugs frequently problems related to controlling this pest feed on reproductive parts of the plant group. and thus are frequently pests of seed crops (Burgess et al., 1983). The plant bug genus Lygus in North America contains several economically Some Lygus spp. have become pests because important species. They feed on a they are usually highly mobile, variety of crops and native plants. Some multivoltine, and oligophagous species are widely distributed and (r-selected), feeding on new growth and broadly overlap the ranges of others. reproductive parts. In contrast to many Great morphological variation in adults other pests in North America, often makes positive identification these species are native difficult. At least some species of attacking a large array of introduced Lygus are parasitized regularly by crops, except in a few instances, such as Braconidae, chiefly in the nymphal an Oregon species that feeds on native stages. Positive identification of Lygus Limnanthes (meadowfoam) (J.D. Lattin, nymphs except in rare instances is not pers. observ.) and a California species now possible. The variations caused by that attacks guayule (Romney, 1946; seasonal factors, the variety of host Bolton et al., 1972; Lattin and Oman, plants, and genetic factors, coupled with 1983). Price (1976), Southwood (1977), the problem of identifying nymphs to and others have pointed out that many pest herbivores are r-selected species, and in the disturbed environments typical of most agroecosystems, such species can liRespectively, Systematic Entomology often colonize faster than their Laboratory, Agricultural Research predators and parasites. Southwood Service, U.S. Department of (1977) stated that polyphagous predators Agriculture, c/o National Museum of are likely to be important in such Natural History, Washington DC 20560, habitats. The heteropteran family and Systematic Entomology Laboratory, Nabidae contains several very common, Department of Entomology, Oregon polyphagous predators found frequently in State University, Corvallis, OR 97331. such disturbed habitats in North

54 America, for example, Nabis alternatus 1975; Scott, 1977; Fye, 1980; Snodgrass Parshley and N. americoferus Carayon et al., 1984). Since not all such plant (Graham and Jackson, 1982). records represent hosts on which eggs are laid, care should be taken to distinguish Lygus bugs, highly mobile as adults, between hosts, where nymphs occur, and often move from disturbed habitats into resting or feeding hosts, where only crop fields (Fye, 1980). Some species adults are found. Often host plant migrate from wild to cultivated plants records in the literature cannot be and have been collected at elevations as associated positively with species of high as 5,000 ft (Glick, 1939; Johnson Lygus because of the difficulty in making and Southwood, 1949). Although most accurate specific identifications and the Lygus spp. are normally multivoltine, lack of voucher specimens, particularly single generations may occur in the in western North America. If voucher northern part of their ranges (Kelton, specimens have been retained from the 1975; Craig, 1983). At least one numerous economic studies (see Graham et species, Lygus unctuosus (Kelton), may al., 1984), some associations can be have only a single generation (Kelton, verified or corrected. Fortunately the 1975; Craig, 1983). Other univoltine widespread Lygus lineolaris is more species of Lygus, for example, L. easily recognized throughout much of its vanduzeei Knight, normally are not range than is the complex group of economically important (Reid et al., western taxa. 1976). Care should be taken in determining the actual number of Because legumes frequently are utilized generations (Shull, 1933; Salt, 1945; as hosts by North American species of Craig, 1983). Lygus, it is curious that L. lineolaris, with a large array of hosts (Snodgrass et Feeding occurs most often on growing tips al., 1984), is not a pest on soybeans, or reproductive parts of the plant, areas even though this species occurs of high nutrients. This is particularly throughout much of the crops range and damaging to plants grown for seed 453 insect species have been recorded (Jeppson and MacLeod, 1946; Craig, 1983; from this crop in North America (Kogan, Rice et al., 1985). According to Scott 1981). The establishment and subsequent (1970, 1983), such feeding might reduce spread of alfalfa in western North seed yield and germination in carrots, America likely affected significantly the tit the plants grown from damaged seed movement and colonization of western fed on by Lygus spp. may show accelerated species of Lygus bugs (Bolton et al., growth and larger plants and roots. 1972). The effect of such a crop on the Conversely, some evidence indicates that widely scattered, naturally occurring such feeding might stimulate increased populations of Lygus remains to be productivity in some crop species (Scott, studied. When positive species 1970). In some instances, the host plant identifications can be combined with may affect adult longevity and fertility accurate host associations, it will be In Lygus bugs (Al—Munshi et al., 1982). possible to examine the status and distribution of some western Lygus Lygus bugs also feed as scavengers and species. This may be an example of facultative predators of . " reverse" island biogeography, where a Predation on living insects probably crop plant provides a corridor for involves moribund individuals or those dispersal between naturally separated undergoing ecdysis (Wheeler, 1976). The populations. laboratory rearing of Lygus spp. may be enhanced by adding food to the DEFINITION AND PLACEMENT OF LYGUS IN THE diet (e.g., Bryan et al., 1976). FAMILY MIRIDAE

Several pest species of Lygus are known The group of bugs commonly referred to as to occur on a wide variety of plants, lygus bugs belongs in the genus Lygus both introduced and native (Stitt, 1949; Hahn and to the plant bug family Miridae, 431colm, 1953; Parker and Hauschild,

55 the largest family in the true bug order the subgenus Exolygus to accommodate it Heteroptera (superorder ). and allies. Leston (1952), in the first About one-third to one-halt of all attempt to evaluate internal Heteroptera are mirids. Although fewer relationships of the genus on a worldwide than 7,000 species were listed in the basis, recognized six subgenera, Carvalho world Miridae catalog (1957-60), including his new subgenus , many have been described since the 1950s, which contained Lygus pallidulus probably bringing the total to 10,000 or (Blanchard) (as Lygus apicalis Fieber, a more. Most mirid workers predict that junior synonym) and the African "lygus the species inventory for the world will bugs." reach 20,000. Within the Miridae, Lygus is included in the largest subfamily, the Lestons work served as the basis for an . According to Carvalho (1957-60), important revision by Kelton (1955a), more than 250 mirine genera were who, by utilizing male and female described by 1955. Of these, Lygus genitalia and external morphology, gave (sensu lato) contained the greatest strong evidence that most of the number of species, about 300. subgenera previously placed in Lygus deserved generic status. He recognized Currently, however, only 34 species are as valid genera Reuter (type- placed in Lygus in North America and species Lygaeus rubicundus Fallen), about 8 are known from the Old World Fieber (type-species Cimex (Kelton, 1975). The reduced tripustulatus Fabricius) (with Exolygus number of species recognized in Lygus Wagner as a junior synonym (type-species deserves some explanation. Historically, Cimex pratensis Linnaeus)), Lygus Hahn the broad definition of the Lygus was (type-species Cimex pabulinus Linnaeus), based largely on the overall similarity Fieber (type-species Cimex kalmii of many species, which were Linnaeus), and Taylorilygus Leston inconsistently broken into several (type-species Lygus simonyi Reuter) similar appearing subgenera. Even so, (appendix). This revision produced the the economic literature on Lygus was result Slater (1950) had predicted should basically stable, and few entomologists several subgenera in Lygus be raised to were concerned that the pestiferous lygus genus, viz, that the economically bugs did not belong in the nominate important lygus bugs would be placed in a subgenus Lygus, that is, until more genus other than Lygus. Because the recently, when the type of Lygus became North American lygus bugs are congeneric more than an academic problem. with Cimex pratensis (the type-species of Exolygus), Keltons revision required The current classification of Lygus is that they be transferred to Exolygus. built primarily on the work of several Kelton (1955a, 1955b) considered Exolygus key workers (appendix). Knight (1917) a junior synonym of Liocoris, meaning, provided the first comprehensive review that if this interpretation was followed, of the North American species. He the lygus bugs would take the generic recognized six species groups of Lygus, name Liocoris. Wagner (1957), however, including his new subgenus . maintained that Exolygus and Liocoris China (1941), on discovering that Distant were not congeneric, leaving the (1904) had designated Cimex pabulinus status of Exolygus problematic. Linnaeus as the type-species of Lygus, described the subgenus To prevent such an upheaval in the (type-species Lygaeus limbatus Fallen) to economic literature, Carvalho, Knight, accommodate what he thought would include and Usinger (1961), with the agreement of (L.) and other British most of the mirid-worker community, "lygus bugs" (China, 1943). Wagner including Kelton, petitioned the (1949), in a revision of the Palaearctic International Commission of Zoological Lygus, noted that the European L. Nomenclature (I.C.Z.N.) to reject Cimex pratensis was not consubgeneric with pabulinus as the type of the subgenus species in other subgenera and described

56 Lygus and to designate Cimex pratensis as to genera of North American Miridae. the type-species. The I.C.Z.N. (Opinion Its simple terminology with numerous 667, 1963) thus ruled to preserve the illustrations makes it a good generic well-known concept of Lygus with the reference. following decisions: At the species level, Keltons (1975) Lygus Hahn, 1833 (fix Cimex revision of North American Lygus is the pratensis Linneaus, 1758, as the best reference to consult. It contains type-species). a key and descriptions of all recognized Exolygus Wagner, 1949 (type-species species, notes on their distribution and hosts, and clarification of earlier Cimex pratensis Linneaus), an misidentifications of Palaearctic objective junior synonym of Lygus species. Although he reevaluated the to be placed on the list of Nearctic fauna and recognized several officially rejected names. synonyms, determination of species remains difficult, even for the Reuter, 1875 (fix Cimex specialist with correctly identified pabulinus Linneaus, 1761, as the specimens for comparison. Most species type-species). of Lygus are multivoltine and have numerous seasonal or color forms, which These changes have insured that the compound the degree of difficulty in economic lygus bugs will remain in the species recognition. In table 1 is a genus Lygus and that Exolygus will summary of overwintering stages, always be a junior synonym because they voltinism, and host plant groups of have the same type-species. Presently, Lygus and associated genera. Current Liocoris is considered distinct from difficulties in associating certain Lygus, but if Keltons conclusions are populations of Lygus with specific names followed, it becomes a junior synonym of indicate that some of the 34 Nearctic Lygus. species may be conspecific. GENERIC AND SPECIES RECOGNITION Palaearctic Taxa Nearctic Taxa For the Palaearctic region, several good references can be used to identify Anyone who has tried to identify species genera and species. Southwood and of Lygus will agree that the genus is Leston (1959) provided a key to the particularly difficult to define. species and genera of the tribe Carvalho (1955) in a monumental effort found in the British Isles. Stichels probably illustrates it best. Of 154 (1958) publication is one of the best mirine genera in his "Keys to the Genera for the European species of Miridae. of the Miridae of the World," Lygus Kiritshenkos (1951) keys to the bugs of falls out at couplet 153, a clear the European U.S.S.R., although having indication that the genus is most easily an outdated generic scheme, can be used diagnosed by eliminating the other more for species identifications. Kerzhners "distinct" genera. Carvalhos study, (1964) key is good for the genera and however, predated Kelton (1955a) and the species found in the European others who published their U.S.S.R.; Vinokurovs (1979) key is interpretations of the Lygus complex. available for the more eastern region of Keltons (1955a) key to genera of the Yakut. Wagners (1970-71) key to the Lygus complex, if used in conjunction Miridae of the Mediterranean region, with the more comprehensive keys of although still using the name Exolygus Blatchley (1926), Knight (1941, 1968), instead of Lygus, is the most recent and and Kelton (1980) to reach the Lygus comprehensive European reference. As in complex, will allow relatively easy North America, the species are variable recognition of the North American and often difficult to recognize with genera. Slater and Baranowskis (1978) certainty. publication contains the only recent key

57 Table 1 General life history and host information of Lygus and other genera previously included in the Lygus complex

Overwintering Number of Genus stage generations Hosts

Agnocoris Adult Multiple (?) Host specific on Salix spp.

Dagbertus Adult and egg (?) Multiple Polyphagous

Lygocoris

Subg. Apolygus Egg Single Polyphagous (?) weeds and trees

Subg. Lygocoris Egg Multiple Polyphagous

Subg. Neolygus Egg Single Host specific on trees and shrubs

Lygus Adult Multiple Polyphagous

Egg Single Host specific

Orthops Adult Multiple (?) Host specific on Umbelliferae

Pinalitus Egg Single Host specific on Picea and Pinus BPP.

Taylorilygus Adult and egg Multiple Polyphagous

1/ Appears to have 2 distinct species groups.

IDENTIFICATION OF NYMPHS of classification, similar to that presented by Wagner (1949), is given. Late-instar nymphs of North American Users of these references need to update Miridae may be recognized using several the generic placement of the species nymphal keys, including DeCoursey treated. (1971), Herring and Ashlock (1971), and Slater and Baranowski (1978). Southwood Akingbohungbe et al. (1973) published (1956) developed a key for determining the only text containing nymphal keys to the instar of cimicomorphan nymphs. the genera of Miridae in North America. Leston and Scudder (1956) gave Their "Keys to the Nymphs of the descriptions and family keys to the Wisconsin Miridae" show that it is nymphs of the British Heteroptera. possible to recognize genera and even Butlers (1923) "Biology of the British species of Miridae in the immature Hemiptera-Heteroptera" contains stages. descriptions, life histories, and hosts of many species, including those in the RELATIONSHIPS OF GENERA PREVIOUSLY Lygus complex found in the British PLACED IN LYGUS Isles. Bech (1969) should be consulted for information on the life history, Agnocoris Reuter. The Holarctic willow- ecology, and nymphs and particularly for feeding genus Agnocoris externally is the long host list of the Palaearctic similar to Lygus, but the genital species of Lygus and related genera. In structures, silky pubescence, and short both of the last texts, an older scheme second antennal segment define a

58 distinct genus (Kelton, 1955a). cervinus (Herrich-Schaeffer), atomarius Although Slater (1950) believed the (Meyer-DUr), and rubricatus (Fallen) female genitalia of Agnocoris were indicated that they were not congeneric rather distinct from those of other with kalmii Linnaeus, the type-species Lygus groups (subgenera), Kelton (1955a) of Orthops. Later, the spruce-feeding suggested that Agnocoris, along with rubricatus was transferred to the Palaearctic genus Cyphodema Fieber, Kelton with the pine-feeding was one of the few genera previously approximatus StAl (Kelton, 1977) and three placed in the Lygus complex that showed other Nearctic species. Kelton (1955a) close relationship to Lygus. considered the umbelliferous-feeding species of the genus Orthops remotely Knightomiris Kelton. The parameres of related to Lygus. Orthops is considered Knightomiris distinctus (Knight) are closely related to the Afro-tropical similar to those of Lygus, but genus Lygidolon Reuter, which has been K. distinctus has a prominent tubercle reviewed by Odhiambo (1960), Ghauri on the margin of the pygophore above the (1971), and Linnavuori (1974). left paramere and the vesica differs in Linnavuori (1975) noted that the having two distinct spiculi (Kelton, African species of Lygidolon, Orthops, 1974). Kelton erected Knightomiris to and Taylorilygus need to be revised and accommodate this single species. should be studied along with the genera Gutrida Kirkaldy, Oreolygus Linnavuori, Lygocoris Reuter. This genus, now and Yngveella Poppius. divided into four subgenera, probably has little relationship to Lygus. Pinalitus Kelton. The genus Pinalitus, Slater (1950) indicated that the erected to accommodate the species subgenus Neolygus does not appear even approximatus StAl, apparently is related closely related to Lygus. Kelton to the Neotropical genus Alda, but it (1955a) confirmed that male and female differs in having a much shorter first genitalia and many external characters antennal segment (Kelton, 1955a). Alda linked the subgenera Apolygus, resembles certain members of the widely Lygocoris, Neolygus, and Stechus. Based distributed genus Fallen and, on this information, Kelton considered like Pinalitus, is not closely related Lygocoris distinct from Lygus [as to Lygus. Liocoris]. Clayton (1982) further supported the distinctiveness of Distant. The species Lygus(, sallei Lygocoris and suggested that the Stal, included in Knights (1917) subgenera Apolygus, Lygocoris, and catchall group I, now is placed in the Neolygus might best be considered as Neotropical genus Proba. Carvalho separate genera. Zheng and Wang (1982, (1952) previously considered Paralygus 1983) and Wang and Zheng (1982), Reuter a junior synonym of Proba. although apparently correctly placing 20 new species from China in Apolygus, Kelton (1955a) noted a superficial incorrectly placed them in the genus resemblance of Proba to Horcias Distant Lygus. As members of the subgenus (the latter is now in part subdivided, Apolygus, they must be placed in the with the North American species genus Lygocoris. Kelton (1971) reviewed transferred to the genus the Nearctic species of Lygocoris, Metriorrhynchomiris Distant (Carvalho redescribed the adults, furnished host and Jurberg, 1974)), but he stated that plant information, and provided a key to the absence of a transverse carina help distinguish species found in Canada between the eyes and the form of the and Alaska. genital structures on Horcias easily separated it from Proba. Orthops Fieber. Wagners (1949) vague definition of Orthops includes a group Sabactus Distant. Another monotypic of heterogeneous species (Kelton, genus known from Sri Lanka, it contains 1955a). Keltons study of the only the species institutus (Distant). Palaearctic species visicola (Puton),

59 Previously this genus was placed in microscope (SEM), are called for and, in Lygus, but Kelton showed that the two fact, have produced some promising genera are not closely related. results on a limited basis (J.D. Lattin and V. Razafimahatratra, unpub.). Kelton. This Nearctic, monotypic genus (Kelton, 1955a) Contemporary biochemical techniques possesses unique characters making it should be used, such as those of Sluss distinct from Lygus. Salignus et al. (1982), together with distinguendus (Knight), a willow-feeding crossbreeding investigations (Graham, species, differs in structure from any 1982). The development of an artificial taxon studied by Kelton (1955a). diet for Lygus makes easier the main- tenance of laboratory cultures for Taylorilygus Leston. Kelton (1955a) study (Debolt, 1982). Sex pheromones considered Lestons subgenus have been detected in several species of Taylorilygus a distinct genus, noting Miridae, including Lygus, and should be that the male and female genitalia investigated further (Boivin and indicated it was not closely related to Stewart, 1982). Adequate samples, well Lygus. All species of Taylorilygus are documented and appropriately preserved, confined to the Afro-tropical region, should be collected over a wide area. except T. pallidulus (Blanchard), a Such samples would also assist in polyphagous "cosmopolitan" species. studies involving geographic variation. Taylor (1947) described most of the Because considerable seasonal variation species, indicated host plants, and in the adults is known to occur (Kelton, provided an identification key. Kelton 1975), samples should be taken during (1955a) considered Taylorilygus most more than one season. closely related to the Neotropical genus Distant. These two genera are It is not now possible to identify similar externally, but the genital nymphs to species accurately. structures and the very short third Well-preserved nymphs associated with antennal segment of Dagbertus will adults should be collected for study. distinguish them (Kelton, 1955a; Slater Some mirid nymphs can be identified to and Baranowski, 1978). Carvalho (1983) species in other genera, but reviewed Dagbertus, providing comparatively little work has been done descriptions of 12 new species, a on nymphal taxonomy (see previous checklist of the species, and a key to section on nymphs). It also is possible help separate them. that useful taxonomic characters might be found on the eggs of Lygus. The SEM PROBLEMS INVOLVING THE TAXONOMY OF NORTH would be an essential investigative tool AMERICAN LYGUS for such work. All the available information should be assembled and Despite efforts to clarify the species analyzed utilizing contemporary level taxonomy of Lygus and related systematic methods. genera, it is difficult to positively identify many commonly encountered Once a more solid systematic base has specimens. This hinders the development been established, it may be possible to of species-specific programs involving, clarify other puzzling questions, for for example, biological control agents. example, the broad geographical ranges The taxonomic difficulty stems chiefly of many species that often overlap those from the inability to determine species of several others. Is this the case, or in Lygus accurately and from their are we unable to recognize other taxa variability throughout their ranges. adequately, or are they the same Macromorphological systematic techniques species? It is clear that there is may have been used to their limit. seasonal variation and, most likely, Micromorphological studies, including geographical variation. We are not yet the use of the scanning electron able to cope fully with these

60 variables. Carefully conducted life RECOMMENDATIONS FOR FUTURE WORK history studies, with voucher specimens, are needed to clarify these problems. (A) Short term Adults The available host plant data present a Micromorphological studies bewildering array of plant taxa with few Biochemical studies, including indications of any ordered associations. allozymes and pheromones Clear distinction should be made between Hybridization studies resting, feeding, and hosts supporting Adequately vouchered and nymphs such as was done by Fye (1980) or preserved samples from broad Snodgrass et al. (1984), who indicate geographical areas when adults or nymphs or both were Nymphs and eggs collected. Damage can occur on crops Procurement of associated where Lygus bugs do not breed and samples oviposit, especially because adults Micromorphological studies readily migrate to and feed on plants (3) General where nymphs do not occur. Accurate, vouchered host data over broad geographical area Careful attention should be given to the Thorough life history studies, phenology of the host plant and the including hosts, phenology, occurrence of Lygus on the plant. and population dynamics Almost certainly some of the apparent Studies of associated confusion over host association is due predators and parasites to host plant shifts in different parts (B) Long term of the bugs range. Fox and Morrow Analysis and synthesis of short- (1981) pointed out that a species may be term information a generalist throughout its range but a Systematic revision of the specialist locally. Species of the genus Lygus genus Lygus would seem to be excellent Phylogenetic studies of Lygus subjects for such an analysis once the spp. and near relatives taxonomy is better known. A species Host plant resistance studies such as Lygus lineolaris, already well defined but very widespread and SOME FINAL QUESTIONS apparently rather polyphagous, would be a fine candidate for such a study. A review of this kind frequently raises more questions than it answers. Our And finally, if a rational approach is knowledge is so rudimentary in some to be taken in seeking possible areas as to make progress difficult. biological control agents, particularly Nevertheless, some intriguing questions in other parts of the world, it is may be raised, the answers to some of essential to know just where the genus which may eventually come from work on Lygus fits in the overall phylogeny of Lygus. the Miridae. A more indepth comparison of the mirine genera is needed using --What makes the native species of contemporary phylogenetic analysis. Lygus move so readily to introduced When we know more about the near plants, including crop plants? relatives of Lygus and where they occur, --Although some Lygus feed on various searches for more effective biological legumes, why have they not control agents are likely to be more transferred to soybeans, even successful. Although there is no though a large number of other guarantee that seeking such agents from insects have done so, including near relatives will produce successful Lygocoris (Apolygus) lucorum results, it does put such efforts on a (Meyer-Diir) (Lattin and Hall, 1983)? more ordered basis (Condit and Cate, --How is it possible to explain the 1982). apparent great range of acceptable

61 host plants for some Lygus ACKNOWLEDGMENTS species? There are species included in the genus that appear We thank V.D. Razafimahatratra, National to be host-plant specific and may University, Malagasy Republic, be typical k-selected species. Madagascar, for sharing his views on some of the problems in the genus Lygus. Many --What adaptive features of Lygus useful suggestions have been made by R.C. spp. enable them to occupy Froeschner, Department of Entomology, (apparently) such a wide geographic National Museum of Natural History range? Can these attributes be (NMNH), Washington, D.C.; R.W. Hodges, identified and included in Systematic Entomology Laboratory, predictive models on pest potential? Agricultural Research Service, USDA, c/o --Some species of Lygus are sometimes NMNH; and A.G. Wheeler, Jr., Bureau of found together on crops. What are Plant Industry, Pennsylvania Department the consequences of this apparent of Agriculture, Harrisburg, Pa. interspecific competition? --Are there special attributes of the pest species of Lygus that allow REFERENCES CITED them to adjust to unstable, disturbed environments and thereby Akingbohungbe, A.E., J.L. Libby, and enable them to become pests in the R.D. Shenefelt. 1973. Nymphs of first place? Are they less of a Wisconsin Miridae. Hemiptera: problem in no-tillage systems? Heteroptera. Univ. Wis. Expt. Sta. Bul. --What can be learned by analyzing R2561, 24 pp. the nature of the predator-parasite complex associated with each Al-Munshi, D.M., D.R. Scott, and H.W. species of Lygus, including those Smith. 1982. Some plant host effects on that are not pests? (Hemiptera: Miridae). --Why havent some Lygus species been Jour. Econ. Entomol. 75:813-815. introduced into other countries accidentally? Bech, R. 1969. Untersuchungen zur --Although many European insects have Systematik. Biologie and bkologie been introduced into North America, wirtschaftlich wichtiger Lygus-Arten. including a large number of (Hemiptera: Miridae). Beitr. Ent. Miridae, where are the common 19:63-103. European species of Lygus? Several European species of Lygus are Blatchley, W.S. 1926. Heteroptera or regularly intercepted at U.S. ports true bugs of eastern North America. 1116 by APHIS Plant Pest Quarantine pp. Nature Pub. Co., Indianapolis, Ind. personnel (pers. observ., T.J. Henry). All earlier reports of Boivin, G., and R.K. Stewart. 1982. European species of Lygus in North Attraction of male green apple bugs, America apparently are based on Lygocoris communis (Hemiptera: Miridae), misidentifications. It is possible to caged females. Can. Entomol. that some of these species are 114:765-766. present in our fauna but have gone undetected. If not, why havent Bolton, J.L., B.P. Goplen, and these species become established? H. Baenziger. 1972. World distribution and historical developments. In Hanson, Quite clearly, although much is known C.H., ed., Alfalfa Science and about Lygus bugs and many authors have Technology, pp. 1-34. Amer. Soc. Agron., contributed to this knowledge, there is Inc., Madison, Wis. much to learn. Bryan, D.E., C.G. Jackson, R.L. Carranza, and E.G. Neeman. 1976. Lygus hesperus: Production and development in the laboratory. Jour. Econ. Entomol. 69:127-129. 62 Burgess, L., J. Dueck, and Clayton, R.A. 1982. A phylogenetic D.L. McKenzie. 1983. Insect vectors of analysis of Lygocoris Reuter the yeast Nematospora coryli in mustard, (Heteroptera: Miridae) with notes on life Brassica juncea, crops in southern histories and zoogeography. M.S. Thesis, Saskatchewan. Can. Entomol. 115:25-30. Univ. Conn., Storrs, 78 pp.

Butler, E.A. 1923. A biology of the Condit, B.P., and J.R. Cate. 1982. British Hemiptera-Heteroptera. 682 pp. Determination of host range in relation H.F. G. Witherby, London. to systematics for stygicus (Hym.: Braconidae), a parasite of Carvalho, J.C.M. 1952. On the major Miridae. Entomophaga 27:203-210. classification of the Miridae (Hemiptera). (With keys to subfamilies Craig, C.H. 1983. Seasonal occurrence and tribes and a catalogue of the world of Lygus spp. (Heteroptera: Miridae) on genera.) Acad. Brasil. Cien. 25:31-110. alfalfa in Saskatchewan. Can. Entomol. 115:329-331. Carvalho, J.C.M. 1955. Keys to the genera of Miridae of the world Deholt, J.W. 1982. Meridic diet for (Hemiptera). Bol. Mus. Goeldi. 11:1-151. rearing successive generations of Lygus hesperus. Ann. Entomol. Soc. Amer. Carvalho, J.C.M. 1957-60. Catalog of 75:119-122. the Miridae of the world. Pt. I (44(1):1-158 (1957)), pt. II (45(2):1-216 DeCoursey, R.M. 1971. Keys to the (1958)), pt. III (47(3):1-161 (1958)), families and subfamilies of the nymphs of pt. IV (48(4):1-384 (1959)), pt. V North American Hemiptera-Heteroptera. (51(5):1-194 (1960)). Arq. Mus. Nac., Proc. Entomol. Soc. Wash. 73:413-428. Rio de Janeiro 48:1-384. Distant, W.L. 1904. The fauna of British India including Ceylon and Carvalho, J.C.M. 1983. Mirideos Burma. Rhynchota. Vol. II. neotropicais CCXXXIII: Genero Dagbertus (Heteroptera). 503 pp. Taylor and Distant--Descrigoes de especies e revisao Francis Printers, London. das que ocorrem na regiao (Hemiptera). Rev. Brasil. Biol. 43:157-176. Fox, L.R., and P.A. Morrow. 1981. Specialization: Species property or local Carvalho, J.C.M., and J. Jurberg. 1974. phenomenon? Science 211:887-893. Neotropical Miridae, CLXXX: On the Horcias complex (Hemiptera). Rev. Fye, R.E. 1980. Weed sources of Lygus Brasil. Biol. 34:49-65. bugs in the Yakima Valley and Columbia Basin in Washington. Jour. Econ. Carvalho, J.C.M., H.H. Knight, and R.L. Entomol. 73:469-473. Usinger. 1961. Lygus Hahn, 1833 (Insecta, Hemiptera); proposed Ghauri, M.S.K. 1971. New species of designation under the plenary powers of Lygidolon Reuter (Hemiptera-Heteroptera: the type-species in harmony with Miridae) infesting wattle in South and accustomed usage. ZH.(S.) 1062. Bul. East Africa. Jour. Entomol. 40:133-138. Zool. Nomencl. 18:281-284. Glick, P.A. 1939. The distribution of China, W.E. 1941. A new subgeneric name insects, spiders and mites in the air. for Lygus Reuter 1875 nec Hahn 1833 U.S. Dept. Agr. Tech. Bul. 673:1-150. (Hemipt.-Heteropt.). Proc. Roy. Entomol. Soc. Lond. 10:60. Graham, H.M. 1982. Interbreeding of Van Duzee and L. desertinus China, W.E. 1943. The generic names of Knight in the field. Southwest. Entomol. British Hemiptera-Heteroptera, with a 7:60-64. check list of the British species. 316 pp. Roy. Entomol. Soc. Lond. Graham, H.M., and C.G. Jackson. 1982. Kelton, L.A. 1975. The lygus bugs Distribution of eggs and parasites of (genus Lvgus Hahn) of North America Lygus spp. (Hemiptera: Miridae), Nabis (Heteroptera: Miridae). Entomol. Soc. spp. (Hemiptera: Nabidae), and Canada Mem. 95:1-101. Spissistilus festinus (Say) (Homoptera: Membracidae) on plant stems. Ann. Kelton, L.A. 1977. Species of the genus Entomol. Soc. Amer. 75:56-60. Pinalitus Kelton found in North America (Heteroptera: Miridae). Can. Entomol. Graham, H.M., A.A. Negm, and L.R. Ertle. 109:1549-1554. 1984. Worldwide literature of the Lygus complex (Hemiptera: Miridae), 1900-1980. Kelton, L.A. 1980. The plant bugs of U.S. Dept. Agr., Agr. Res. Serv., the Prairie Provinces. Heteroptera: Bibliogr. Lit. Agr. No. 30, 205 pp. Miridae. Agr. Can. Pub. 1703, 408 pp. Ottawa. Herring, J.L., and P.D. Ashlock. 1971. A key to the nymphs of the families of Kerzhner, I.M. 1964. Order Hemiptera Hemiptera (Heteroptera) of America north (heteroptera). Family Miridae of Mexico. Fla. Entomol. 54:207-212. (Capsidae). In Bei-Bienko, G.Y., ed., Keys to the Insects of the European International Commission of Zoological U.S.S.R., vol. I, pp. 911-1003, Nomenclature. 1963. Opinion 667. Bul. Apterygota, Paleoptera, Hemimetabola. Zool. Nomencl. 20:270-271. Zool. Inst. Acad. Sci. U.S.S.R., Leningrad. [English transl., 1967; Jeppson, L.R., and G.F. MacLeod. 1946. Russian edition, 1964] Lygus bug injury and its effect on the growth of alfalfa. Hilgardia. 17:165-188. Kiritshenko, A.N. 1951. True bugs of the European U.S.S.R. (Hemiptera). Key Johnson, C.G., and T.R.E. Southwood. and bibliography. 423 pp. Acad. Sci. 1949. Seasonal records in 1947 and 1948 U.S.S.R., Moscow-Leningrad. [In Russian] of flying Hemiptera-Heteroptera, particularly Lygus pratensis L., caught Knight, H.H. 1917. A revision of the in nets 50 ft to 3,000 ft above ground. genus Lygus as it occurs in America north Proc. Roy. Entomol. Soc. Lond. (A) of Mexico, with biological data on the 24:128-130. species from New York. Cornell Univ. Agr. Expt. Sta. Bul. 391:555-645. Kelton, L.A. 1955a. Genera and subgenera of the Lygus complex Knight, H.H. 1941. The plant bugs, or (Hemiptera: Miridae). Can. Entomol. Miridae, of Illinois. Ill. Nat. Hist. 87:277-301. Surv. Bul. 22:1-234.

Kelton, L.A. 1955b. Species of Lygus, Knight, H.H. 1968. Taxonomic review: Liocoris, and their allies in the Prairie Miridae of the Nevada Test Site and the Provinces of Canada. Can. Entomol. Western United States. Brigham Young 87:531-556. Univ. Sci. Bul. 9(3):1-282.

Kelton, L.A. 1971. Review of Lygocoris Kogan, M. 1981. Dynamics of insect species found in Canada and Alaska adaptations to soybeans: Impact of (Heteroptera: Miridae). Entomol. Soc. integrated pest management. Environ. Canada Mem. 83:1-87. Entomol. 10:363-371.

Kelton, L.A. 1974. Knightomiris new Lattin, J.D., and B.B. Hall. 1983. genus, for Lygus distinctus (Heteroptera: Lygocoris (Apolygus) lucorum (Meyer-DUO Miridae). Can. Entomol. 105:1417-1420. 1843 (Hemiptera: Miridae). Potential host of parasites for biological control of Lygus. Oreg. State Univ., Syst. Entomol. Lab. Inform. Sheet, 2 pp.

64 Sluss, T.P., H.M. Graham, and Wagner, E. 1949. Zur Systematik der E.S. Sluss. 1982. Morphometric, Gattung Lygus Hhn. (Hem. Het. Miridae). allozyme, and hybridization comparisons Verh. Ver. Naturw. Heimatf., Hamburg. of four Lygus species (Hemiptera: 30:26-40. Miridae). Ann. Entomol. Soc. Amer. 75:448-456. Wagner, E. 1957. Das Lygus-Liocoris Problem (Hem. Het. Miridae). Deut. Snodgrass, G.L., W.P. Scott, and Entomol. Ztschr. 4:91-94. J.W. Smith. 1984. An annotated list of the host plants of Lygus lineolaris Wagner, E. 1970-71. Die Miridae Hahn, (Hemiptera: Miridaerfrrthe Arkansas, 1831, des Mittelmeerraumes and der Louisiana, and Mississippi Delta. Jour. Makaronesischen Inseln (Hemiptera, Ga. Entomol. Soc. 19:93-101. Heteroptera). Teil 1. Entomol. Abh. Mus. Tierk. Dresden, Sup. 37:1-484. Southwood, T.R.E. 1956. A key to [1970:1-273; 1971:274-484] determine the instar of an heteropterous larva. Entomologist 89:220-222. Wang, X., and L. Zheng. 1982. Three new species of Lygus of the subgenus Apolygus Southwood, T.R.E. 1977. The relevance from Fujian, China (Hemiptera: Miridae). of population dynamic theory to pest Wuyi Sci. Jour. 2:118-123. status. In Cherrett, J.M., and G.R. Sagar, eds., Origins of Pest, Parasite, Wheeler, A.G., Jr. 1976. Lygus bugs as Disease and Weed Problems, pp. 35-54. facultative predators. In Scott, D.R., 18th Symp. Brit. Ecol. Soc., Bangor, and L.E. OKeeffe, eds., Lygus Bugs: Host 12-14 Apr. 1976. Blackwell Sci. Pub., Plant Interactions, pp. 28-35. Univ. Oxford. Idaho Press, Moscow.

Southwood, T.R.E., and D. Leston. 1959. Zheng, L., and X. Wang. 1982. New Land and water bugs of the British species of Lygus bugs from China. Isles. 436 pp. Frederick Warne Co. Entomotaxonomia 5:47-59. Ltd., London. Zheng, L., and X. Wang. 1983. New Stichel, W. 1958. Illustrierte species and records of Lygus (subg. Bestimmungstbellen der Wanzen. II. Apolygus) from China. Acta Zootaxonom. Europa (Hemiptera-Heteroptera Europae). Sinica. 8:422-433. Vol. 2, 24 Heft, pp. 737-768. Martin-Luther, Berlin-Hermsdorf.

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Vinokurov, N.N. 1979. Keys to the fauna of the U.S.S.R. Heteropterous insects of Yakutia. 231 pp. Zool. Inst., Acad. Sci. U.S.S.R., Leningrad. [In Russian]

66 APPENDIX Subgenus Apolygus (type-species limbatus) The following classifications of Lygus Subgenus Exolygus Wagner are from Knight (1917) to the present: (type-species pratensis) Subgenus Lygus (1) Knight (1917) treated only North (type-species pabulinus) American taxa: Subgenus Orthops Genus Lygus Hahn (type-species kalmii) Group I (pratensis group; considered Lygus lineolaris Leston (1952) gave a world review of (Palisot) a junior synonym of Lygus and subgenera: Lygus pratensis (Linneaus)) Genus Lygus Group II (campestris group) Subgenus Agnocoris campestris Linneaus (subg. (type-species rubicundus) Orthops Fieber) Subgenus Exolygus distinctus Knight (now in (type-species pratensis) Knightomiris Kelton) Subgenus Lygus rubicundus Fallen (subg. (type-species pabulinus) Agnocoris Reuter) Subgenus Neolygus sallei StAl (now in Proba (type-species communis Knight) Distant) Subgenus Apolygus, a junior Group III approximatus StAl (now synonym (type-species limbatus) in Pinalitus Kelton) Subgenus Orthops Group IV (type-species kalmii) fasciatus Reuter (now in Subgenus Taylorilygus Leston Dagbertus Distant) (type-species simonyi Reuter) olivaceus Reuter (now in Dagbertus) Kelton (1955a) treated Lygus and Group V associated genera: apicalis Fieber (now in Genus Agnocoris Taylorilygus Leston) (type-species rubicundus) Group VI (communis group; subg. Genus Cyphodema Fieber Neolygus Knight) (type-species instabilis Lucas) contains 39 species in North Genus Dagbertus America (type-species darwini Butler) Genus Liocoris China (1943) treated British genera: (type-species tripustulatus) Genus Liocoris Fieber Genus Exolygus, a junior synonym (type-species tripustulatus (type-species pratensis) (Fabricius)) Genus Lygus Genus Lygus (type-species pabulinus) Subgenus Agnocoris Subgenus Apolygus (type-species rubicundus) (type-species limbatus) Subgenus Apolygus China Subgenus Lygus (type-species limbatus Fallen) (type-species pabulinus) Subgenus Lygus Subgenus Neolygus (type-species pabulinus (type-species communis) Linnaeus) Subgenus Stechus Distant Subgenus Orthops (type-species libertus Distant) (type-species kalmii Linnaeus) Genus Orthops Fieber (type-species kalmii) Wagner (1949) treated Palaearctic Genus Pinalitus genera: (type-species approximatus) Genus Lygus (group III of Knight (1917)) Subgenus Agnocoris Genus Proba (type-species rubicundus)

67 (type-species gracilis Distant) (sallei group of Knight (1917)) Genus Sabactus Distant (type-species institutus Distant) Genus Salignus (type-species distinguendus Reuter) (in group I of Knight (1917)) faylorilygus (type-species simonyi)

(6) Current scheme, ruling of International Commission of Zoological Nomenclature (1963); other generic concepts (not listed) follow Kelton (1955a, 1974): Genus Liocoris (a subjective junior synonym of Lygus; currently considered a distinct genus) Genus Lygocoris (type-species pabulinus) Subgenus Apolygus (type-species limbatus) Subgenus Lygocoris (type-species pabulinus) Subgenus Neolygus (type-species communis) Subgenus Stechus (type-species libertus) Genus Lygus (type-species pratensis) Genus Exolygus (same type-species; an objective junior synonym of Lygus)

68