Planthoppers (Hemiptera: Fulgoromorpha) are of concern to agriculture in the southeastern United States because of their potential to cause significant damage to economically important plants. These keys are intended to aid diagnosticians attempting to identify planthopper crop pests. This work includes lists of pathogen vectors and those species considered pests of economically important plants grown in the region, brief descriptions of planthopper collecting and curating techniques, a summary of morphological features used for identification, a revised key for identification of planthoppers to family, a key to the economically important delphacids, and a list of literature useful for planthopper identification.
The planthoppers are a cosmopolitan group of insects placed in the infraorder Fulgoromorpha (=superfamily Fulgoroidea) which includes approximately 9,000 described species in 20 families. The vast majority of planthoppers feed on the phloem tissues of woody or herbaceous plants; however, some planthoppers feed on fungi, mosses, horsetails, or ferns (Wilson et al. 1994; Wheeler 2003). Their life histories range from highly polyphagous species that feed on numerous taxa of unrelated plants to strictly monophagous species that feed on only a single host plant species. Many planthoppers are univoltine and overwinter in the temperate zones in the egg stage; others are multivoltine where the number of generations per year depends on temperature and, perhaps, photoperiod, and many overwinter as nymphs or adults.
In this paper, I provide a brief survey of planthoppers of concern to agriculture in the southeastern United States. This survey includes lists of pathogen vectors and those species considered pests of economically important plants grown in the region, brief descriptions of planthopper collecting and curating techniques, a summary of morphological features used for identification, a revised key for identification of planthoppers to family, a key to the economically important delphacids, and a list of literature useful for planthopper identification.
The Economically Important Planthoppers
Planthoppers are of concern to agriculture because several species are significant pests of a number of important crop plants. A list of economically important species and their host plants was provided by Wilson & O'Brien (1987); many of the species included in their list are of relatively minor economic importance in that they have been reported as pests on only one or a few occasions and/or attack plants of minor economic importance. Several planthopper species are of major importance because they reach high population densities thereby damaging crops and/or they are vectors of bacterial, phytoplasma, or viral pathogens. Planthoppers found to serve as pathogen vectors include 36 species in 4 families (Table 1). As well, 8 species in 7 families are not known to be pathogen vectors but are considered pests due to population eruptions on economically important plants; 5 other species have been introduced to the United States and could ultimately prove to be of economic significance (Table 2). The planthopper species considered pests of crops of importance in the southeastern United States--corn, rice, sugarcane, and palms--and selected studies on their biology are listed in Table 3.
Planthopper Collecting and Curating Techniques
Collecting Techniques. The method employed for most efficiently collecting planthoppers largely depends upon the structure of the host plant. Those on woody plants can be collected individually by knocking specimens into a vial, by use of an aspirator with a relatively large opening, or by putting a sheet or large net under the foliage and striking the branches above. Planthoppers on herbaceous plants can be collected with a sweep net with a very deep net bag which is slowly opened and the planthoppers collected with an aspirator as they crawl toward the opening. Another type of sweep net is constructed of a fine woven translucent plastic netting that retains its open shape; after sweeping, this type of net is held up toward the sun, the planthoppers tend to congregate at the back of the net and can be collected with an aspirator. As many planthoppers tend to live within the thatch near the ground, collecting them requires sitting on the ground, pushing the plants aside, then waiting for the insects to crawl up the plants where they can be sucked up in an aspirator (Beamer, L. 1946). A more efficient means of collecting in this type of habitat is to employ a vacuum, either a “D-vac” which is very heavy and has a somewhat unreliable engine or a modified leaf blower/vacuum which is much lighter and more reliable (Wilson et al. 1993). The net bag at the end of the vacuum can be placed in a plastic jar containing cotton balls soaked in ethyl acetate and the specimens sorted out later, or the bag can be emptied into a sweep net and the specimens collected with an aspirator. Planthoppers also can be collected with Malaise traps, Sante canopy traps, window traps (Weber & Wilson 1981), and blacklights. Blacklights are useful for collecting achilids, cixiids, and some dictyopharids but are of limited value in collecting certain delphacids and caliscelids as the vast majority of their populations are composed of brachypters.
Curating and Specimen Preparation. Collected planthoppers may be killed by placing them directly into 70% ethyl or isopropyl alcohol, or putting specimens in killing jars containing a cotton ball or plaster bottom soaked in ethyl acetate, or by freezing specimens. Nymphal specimens must be stored in vials, preferably with caps with plastic cone inserts, filled with 70% ethyl or isopropyl alcohol; adults may be stored this way but colors will usually bleach out. Adult specimens are usually pinned or glued to a point on the right side of the specimen. Label data accompanying the specimen should include locality (country, state or province, county or district, nearest town, specific location, and if available, GPS coordinates), date, collector, and, if possible, host plant.
Accurate species identification in most planthopper taxa requires examination of the structures of the male genitalia; unfortunately, for many taxa, it is not possible to identify females to species, and in some cases, to genus level. Idenfication of males to species usually requires removing the abdomen with a pair of fine forceps or the point of an insect pin, then placing the abdomen in a 10% potassium hydroxide (KOH) solution for 12-24 h at room temperature (small, lightly sclerotized specimens may require as little as 4-8 h or less in the KOH solution). An efficient means of processing a relatively large number of specimens is to fill wells of a 96-well tissue culture plate with water, place a KOH pellet in each well containing water, then place an abdomen in a well. The pinned specimen is then placed in a Schmidt box or foam bottom insect drawer that has been marked with grid locations corresponding to those on the 96-well tissue culture plate (A1-H12). To examine the genitalia, remove the abdomen from the KOH solution and place it in a deep depression slide filled with water; let it soak in the water for a few minutes then place it in a depression slide filled with glycerine. If the genitalic structures are not clearly visible, hold the pygofer with a pair of fine forceps or the point of an insect pin then gently move the anal tube caudoventrally, or push the connective attached to the anterior base of the aedeagus caudally. This will usually force the aedeagus, anal tube, and styles out of the pygofer. After examination of the genitalia, fill a genital vial with glycerine, place the abdomen into the vial, cap the vial, then pin the vial through the cap under the specimen.
This brief review of planthopper external morphology should provide enough basic information to allow effective use of the keys for identification. More complete treatments are provided by O'Brien & Wilson (1985) for all families, Asche (1985) for delphacids, Freund & Wilson (1995) for acanaloniids, and McPherson & Wilson (1995) for dictyopharids. Overviews of the anatomy of the male genitalia for selected taxa are given by Muir (1926a); Fennah (1945); Bourgoin (1990); and Yang & Chang (2000). Descriptions and illustrations of the anatomy of the female genitalia are provided by Heady & Wilson (1990) and Bourgoin (1993).
Planthoppers can be separated from members of the Cicadomorpha by the location of the antennae which are ventral to the compound eyes (except in one cixiid subfamily in which the compound eyes are positioned anteroventrally to the compound eyes but are partially surrounded by cup-like concavities); the enlarged antennal pedicel bearing wart-like sensilla; the presence, in most taxa, of pad-like tegulae at the base of the forewings; the presence, again, in most taxa, of a “Y-vein”, that is, two anal veins coalescing on the clavus of the forewing to form a “Y-shaped” set of veins; the elongate, widely separated base of the mesothoracic coxae; and the lack of rows of setae along the shaft of each metathoracic tibia as in Cicadellidae.
Head. The head in planthoppers ranges from a broad, short head to those that are strongly laterally compressed or some that have an elongate straight or curved projection extending well beyond the compound eyes. The dorsal aspect of the head is termed the vertex which may be separated from the anterior or anteroventral frons by a transverse carina or, in those planthoppers with broadly rounded heads, not be demarcated from it. The frons, in all but one family, is separated from the gena on each side by a longitudinal external lateral carina; as well, the frons may bear a median longitudinal carina and/or internal longitudinal lateral carinae. Posteroventral to the frons is the clypeus from which the three-segmented beak extends. Some planthoppers have a median ocellus on the frons; most have a lateral ocellus between the frons and gena. The compound eyes are generally large and may be strongly notched ventrally; in some subterranean species the eyes may be reduced or absent. The three segmented antennae in almost all planthoppers are situated ventral to the compound eyes; in some cixiids the antennae are in a cup-like concavity located anterior to the eyes. The basal antennal antennal segment is termed the scape, the middle segment which may be elongate and/or foliose is the pedicel, the terminal segment consists of a bulbous base and elongate, seta-like flagellum.
Thorax. The pronotum is generally short and collar-like and may bear a median longitudinal carina and a pair of lateral carinae. The mesonotum is generally subtriangular and may bear a median longitudinal carina and a pair of lateral carinae; a transverse suture demarcates a small triangular piece at the apex of the mesonotum in tropiduchids and some lophopids. The fore wings may be very large with numerous veins or greatly reduced as in brachypters and may be opaque, concolorous with the body or brightly colored, or completely or partially translucent. The subtriangular anal region of the forewings, or clavus, is set off from the rest of the wing by the postcubital vein which may or may not reach the edge of the wing. The clavus typically bears a “Y-shaped” vein and, in flatids, has numerous pustules on its surface. In some taxa, some or all of the forewing veins may bear enlarged pustules. The hind wings may be almost as large as the forewings or greatly reduced or absent. The hindwings of fulgorids have a characteristic reticulate venation in the anal region. The metathoracic or hind legs have numerous features useful for identification. The tibia has a row of apical spines on the plantar surface and usually bears large lateral spines along the tibial shaft. Delphacids have a characteristic metatibial spur which may be spike-like or foliose and with or without teeth on its inner margin. The tarsus consists of three tarsomeres: the basal or first tarsomere bears a row of apical teeth, the second tarsomere may have a row of apical teeth, one tooth on each side or may be lacking teeth; the third tarsomere terminates in a pair of claws and a central arolium.
Abdomen. Some planthoppers have sound producing tymbals which consist of internal apodemes in the basal abdominal segments and a subrectangular piece of the first abdominal tergite. The sounds made by planthoppers are species specific courtship signals detected via substrate vibrations.
The structures of the male external genitalia are necessary for accurate species identification in most groups of planthoppers. The male genital capsule is a subcylindrical pygofer and represents the modified 9th abdominal segment. The pygofer may have lateral and/or ventral caudally-directed lobes or spines and, in delphacids, may have a partial dorsoventral wall or diaphragm. The diaphragm may bear lobes, spines or other forms of diaphragm armature on its median ventral margin. The anal tube, the 10th abdominal segment, is usually moveable and often bears spines or lobes on its caudal margin. The styles are a pair of clasper-like structures emanating from the ventrocaudal aspect of the pygofer. The styles may be elongate and can have spines or teeth or bear lobes or keels or, in some taxa, they can be relatively small and club-shaped. A “Y-shaped” connective attaches the base of the styles to the base of the aedeagus. The intrommitent organ, or aedeagus, ranges in shape from a simple tube-like structure to a complex elaborate entity bearing numerous spines and, in some taxa, inflatable translucent lobes.
Terminology used in describing female genitalia follows Heady & Wilson (1990). The external female genitalia, collectively referred to as the ovipositor, may be “orthopteroid” or “fulgoroid”. In the “orthopteroid ovipositor” the fused median gonopophyses (=valvula) of the 9th abdominal segment often have a serrated dorsal aspect and serve as a saw-like structure for depositing eggs, usually into plant tissues. The lateral gonopophyses of the 9th abdominal segment and the gonopophyses of the 8th segment serve in egg deposition and may coat the eggs with wax. In some taxa, these structures are reduced and/or modified and very large wax plates are present. The “fulgoroid ovipositor” may be modified for raking particles prior to egg deposition in the soil or on the ground or for depositing eggs in plant tissue. In those that insert eggs into plant tissue the fused gonopophyses of the 8th abdominal segment serve as the saw-like deposition structure and the lateral gonopophyses of the 9th abdominal segment as protective covers and/or egg guide.
Identification of Planthoppers
There are 196 species in 11 families of planthoppers recorded from the southeastern United States (Wilson & McPherson 1980a; Wilson, unpubl. data). Most of these species are of no known economic significance; in fact, many are rare and little is known about their life cycles and hosts. A few species present in the region are of economic importance. As well, there are several species that could be imported by accident or on purpose into the region. To aid in identifying taxa of potential economic importance, keys to the 20 planthopper families and to the economically significant delphacids are included. The key to families has been adapted from O'Brien & Wilson (1985). Since publication of their key, the following family-level changes have been made: 18 genera of Issidae were transferred to Nogodinidae (Fennah 1984); the family Caliscelidae was established to include the former issid subfamilies Caliscelinae and Ommatidiotinae (Emeljanov 1999); the family Acanaloniidae was reestablished and includes the former issid subfamilies Acanaloniinae, Tonginae, and Trenopinae (Emeljanov 1999); and the family Achilixiidae was subsumed within Cixiidae (Liang 2001). Planthopper families with economically important species are designated with an asterisk (*).
The family Acanaloniidae is identified as one that includes species of potential economic importance because Acanalonia conica (Say), while not a significant pest in the United States, has been introduced to Sicily (D'Urso, personal communication). This species has a similar life history and feeding habits to Metcalfa pruinosa (Say), also not a significant pest in the United States, which was introduced to Italy from the United States in the late 1970s and has spread from Spain and southern France to Austria, Slovenia, and Greece (Wilson & Lucchi 2001). Acanalonia conica is often found in mixed nymphal feeding assemblages with M. pruinosa (Wilson & McPherson 1980b) and could become a pest in Europe. As such, it joins the native US species, M. pruinosa and Prokelisia marginata Van Duzee (Seljak 2004) that have recently been introduced to Europe and may be intercepted at United States ports of entry. The life histories and descriptions and illustrations of the immatures of A. conica, M. pruinosa, and similar associated species are provided by Wilson & McPherson (1981a, 1981b).
There are no recent comprehensive keys to the genera and species of a number of families that include economically significant species (e.g., Flatidae). A list of keys that identify species in these taxa and those that survey taxa on selected economically significant crops is provided in Table 4. The following key to delphacids of potential economic importance includes species present in the United States, whether native or introduced, and known to be of economic significance, viral or phytoplasma vectors that could be introduced to the US, and those that are significant pests of crops grown in the United States. Several species recorded as transmitters of viral pathogens based only on laboratory or greenhouse studies with no apparent field evidence are not considered significant pests and, thus, are not included. As well, species that are vectors of pathogens of crop plants of little significance to agriculture in the southeastern United States are not included (e.g., Javesella spp. except for the ubiquitous J. pellucida (Fabricius)). A few common species that are likely to be frequently collected and those that can easily be confused with major pests are included in the key (e.g., Caenodelphax teapae (Fowler), Nilaparvata wolcotti Muir and Giffard). Finally, some taxa, such as Sogatella and Tagosodes, include numerous species, some of which could be introduced to the southeastern United States. If specimens fail to fit the key and illustrations given below, then the taxonomic literature on these taxa should be consulted (e.g., Asche & Wilson 1990; also, see Table 4). In order to ensure accurate identification of these and other delphacid taxa, species identifiers should always compare structures of the male genitalia with either the illustrations provided in this paper or with those in the works listed in Table 4. Figures accompanying the keys were redrawn from Muir & Giffard (1924); Muir (1926b); Doering (1940); Zimmerman (1948); Caldwell & Martorell (1951); Wilson & McPherson (1980c); Asche (1985); O'Brien & Wilson (1985); Tsai & Wilson (1986); Wilson & Claridge (1991); Wilson & Tsai (1992); Wooten et al. (1993); Freund & Wilson (1995); and Holzinger et al. (2003).
Key to the Families of Planthoppers
1. Hind tibia with a large movable spur at apex (Fig. 1)
-Hind tibia without a movable spur at apex (Figs. 2-4)
2. Second tarsomere of hind legs with a row of apical spines (Fig. 2)
-Second tarsomere of hind legs with one apical spine on each side (Fig. 3) or spines absent (Fig. 4)
3. Hindwings with numerous cross veins near apex and in anal area; head usually with a transverse suture separating vertex from frons (Fig. 5); aedeagus with inflatable lobes
-Hindwings without cross veins near apex or in anal area; head without a transverse suture separating vertex from frons; aedeagus variable
4. Forewings overlapping posteriorly (Fig. 6); body usually flattened
-Forewings not overlapping posteriorly; body variable
5. Forewings with tubercles on one or both claval veins (Fig. 7); beak with apical segment longer than wide
-Forewings usually without tubercles on claval veins; if so, then all veins with tubercles or beak with apical segment subequal in length and width
6. Forewings with tubercles on claval veins and beak with apical segment subequal in length and width; styles much longer than pygofer; anal tube not moveable, attached to pygofer
-Forewings without tubercles on claval veins or with tubercles on all veins; beak with apical segment longer than wide; styles shorter than length of pygofer; anal tube moveable
7. Frons with two or three median carinae and/or head with elongate anterior projection (Fig. 8); if not, then tegulae absent
-Frons with one median carina (Fig. 9); head usually without elongate anterior projection; tegulae present
8. Forewings usually with tubercles on veins; abdominal tergites 6-8 subrectangular; females with caudally directed wax plates on tergite 9 and a spike-like ovipositor, or wax plates absent and ovipositor sword-shaped
-Forewings without tubercles on veins; abdominal tergites 6-8 chevron shaped, females with wax plates on tergites 7-9; female genitalia greatly reduced
9. Second tarsomere of hind legs with one apical spine on either side (Fig. 3)
-Second tarsomere of hind legs without apical spines on either side (Fig. 4)
10. Frons with lateral carinae
-Frons without lateral carinae (Fig. 10)
11. Mesonotum with a posterior transverse suture (Fig. 11); forewings with few or no cross veins anterior to nodus, with numerous veins posterior to nodus
-Mesonotum usually without a posterior transverse suture; forewings with sparse venation or dense venation throughout
12. Beak with apical segment subequal in length and width; styles much longer than pygofer; anal tube not moveable, attached to pygofer
-Beak with apical segment longer than wide; styles shorter than length of pygofer; anal tube moveable
13. Forewings with tubercles between veins on clavus (Fig. 12) and with numerous costal crossveins
-Forewings without tubercles on clavus; usually without numerous costal crossveins
14. Ovipositor laterally compressed, gonopophyses of the 8th abdominal segment bearing apical teeth (Fig. 14); pronotum extending anteriorly beyond middle of eyes (Fig. 13), or forewings usually with reticulate venation and hind tibiae without lateral spines
-Ovipositor not laterally compressed, gonopophyses of the 8th abdominal segment without apical teeth (Fig. 15); pronotum not extending anteriorly beyond middle of eyes; forewings of macropters with normal venation; hind tibiae with lateral spines
15. Pronotum extending anteriorly beyond middle of eyes (Fig. 13); clypeus with lateral carinae; macropterous or brachypterous; hind tibia with lateral spines
-Pronotum extending not much beyond posterior aspect of eyes; clypeus without lateral carinae; macropterous, often with reticulate venation; hind tibia usually without lateral spines
16. Frons with lateral carinae bordering a large disc-like or elongate areolet (Fig. 16); usually brachypterous
-Frons with median carina, with or without lateral carina (Fig. 17); if lateral carinae present, not enclosing a central areolet; macropterous
17. Brachypterous, or forewings barely exceeding beyond the apex of the abdomen and with apical venation strongly carinate (southern Africa)
-Macropterous, forewings almost always exceeding well beyond the apex of the abdomen, venation not carinate
18. Eyes reduced, body white, brachypterous, adults subterranean
-Eyes not reduced, body pigmented, macropterous with strongly carinate apical veins, adults not subterranean
19. Forewings at least twice as long as wide; claval vein extending ca. 2/3 to 3/4 distance to caudal aspect of wing
-Forewings broadly triangular, almost as wide as long; claval vein extending almost to caudal aspect of wing (Fig. 18)
20. Clypeus with lateral carinae; vertex with length more than 1/3 width, frons usually longer than wide and with 1-3 longitudinal carinae
-Clypeus without lateral carinae; vertex with length less than 1/3 width, frons wider than long with obscure median carina or carina absent
Key to the Economically Important Delphacidae*
1. Hind legs with lateral spines on first (basal) tarsomere (Fig. 19)
-Hind legs without lateral spines on first tarsomere (Fig. 1)
2. Pygofer with process on ventral margin (Figs. 20, 24)
-Pygofer without processes on ventral margin
3. Pygofer process with lateral spines (Fig. 20); genitalia as in Figs. 21-23
-Pygofer with three small processes without lateral spines (Fig. 24); genitalia as in Figs. 25-27
4. Anal tube with elongate spines; styles not bifurcate; genitalia as in Figs. 28-30
-Anal tube with very small upturned spines or lacking spines (Figs. 31, 33)
5. Anal tube with very small upturned spines (Fig. 31), aedeagus as in Fig. 32
-Anal tube lacking spines (Fig. 33), aedeagus as in Fig. 34
6. Mesonotum light brown to black with median longitudinal pale stripe; genitalia as in Figs. 36-46, Figs. 50-53
-Mesonotum without median longitudinal pale stripe; genitalia as in Figs. 48, 49, Figs. 54-63, Figs. 64-75
7. Pygofer with diaphragm margin thickened and U-shaped, aedeagus with dorsal and ventral elongate rows of teeth (e.g., Fig. 37)
-Pygofer with diaphragm margin not thickened and U-shaped, aedeagal teeth, if present, not arranged as above (e.g., Fig. 50)
8. Frons dark brown, carinae often pale (Fig. 35); genitalia as in Figs. 36-38
-Frons pale yellow (Figs. 39, 43); if frons brown then styles as in Fig. 46
9. Sides of head beneath eyes dark brown (Fig. 39); genitalia as in Figs. 40-42
-Sides of head beneath eyes pale yellow (Fig. 43) or dark brown; genitalia as in Figs. 44-46
10. Sides of head beneath eyes pale yellow (Fig. 43); forewing without dark marking at apex of clavus
-Sides of head beneath eyes dark brown; frons pale or light brown; forewing with dark marking at apex of clavus
11. Frons with median carina forked near ventral aspect of eyes, dorsal half of frons dark with pale spots, ventral half pale (Fig. 47); genitalia as in Figs. 48, 49
-Frons with median carina forked near dorsal aspect of eyes, frons not darker dorsally and lighter ventrally
12. Styles broad at apex, aedeagus with numerous ventral teeth (Figs. 50-51)
-Styles slender at apex, aedeagus with one row of ventro-lateral teeth on each side (Figs. 52-53)
13. Head narrow, produced well beyond eyes; body green to yellow; anal tube without spines, styles with small, apical lobes, aedeagus elongate, ribbon-like (Figs. 54-56)
-Head broad, not produced much beyond eyes; body not green
14. Forewings almost entirely dark black
-Forewings clear or with dark markings
15. Forewings dark with pale transverse stripe; anal tube with bifurcate posterocaudal spine on each side (Figs. 57-58)
-Forewings dark without pale transverse stripe; anal tube with minute teeth on posterocaudal aspect (Figs. 59-60)
16. Forewings with dark markings in apical half; aedeagus slender with spine-like dorsal projections (Figs. 61-63)
-Forewings without dark markings in apical half; aedeagus not as above
17. Styles splayed laterally; aedeagus bent strongly ventrally (Figs. 64-66)
-Styles oriented dorsoventrally; aedeagus directed caudad
18. Styles each with elongate rounded process at apex; aedeagus without dorsal teeth (Figs. 67-69)
-Styles each without elongate rounded process at apex
19. Mesonotum black; aedeagus curved ventrally (Figs. 70-71)
-Mesonotum light brown to straw yellow; aedeagus straight with minute dorsal teeth near apex; pygofer with “y-shaped” dorsal armature (Figs. 72-75)
Note-to ensure accurate species identification always compare the dissected male genitalia with illustrations in the appropriate publications.
I thank Dr. Amanda Hodges, Entomology and Nematology Department, University of Florida, Gainesville, for encouragement and for efforts spent organizing the “Homoptera Workshop”; Dr. Susan Halbert, Division of Plant Industry, Florida Department of Agriculture and Consumer Services, Gainesville, for enthusiasm and very fruitful discussions about some of the planthoppers introduced into Florida; the anonymous reviewers whose suggestions greatly improved the manuscript; and the participants of the “Homoptera Workshop” who asked all the right questions and, by doing so, helped improve the keys immensely.
Planthopper vectors and pathogens of economically important plants.1
(Continued) Planthopper vectors and pathogens of economically important plants.1
Non-vector planthoppers of economically important plants of concern in the southeastern United States.
Selected biological studies on the principal planthopper pests of the major economically important plants in the southeastern United States.
Keys for identification of planthoppers in economically significant taxa.