Asthenopholis Brenske, 1898

Harrison, James G., 2009, A taxonomic revision of the African leaf chafer genus Asthenopholis Brenske, 1898 (Coleoptera: Scarabaeidae: Melolonthinae): a SEM study, Zootaxa 2225, pp. 1-48 : 4-6

Genus Asthenopholis Brenske, 1898

Asthenopholis Brenske 1898: 388 –390. Arrow 1902: 97 –98; Péringuey 1904: 277 (key), 285–288; Dalla Torre 1912: 182 (catalogue); Moser 1913: 341 –342; Kolbe 1914: 352; Arrow 1917: 60 –61; Arrow 1943: 784; Lacroix 2008: 236, 239 (key); 2009 (website). Type species: Asthenopholis transvaalensis Brenske, 1898: 389 a junior synonym of Asthenopholis adspersa ( Boheman, 1857) , here designated.

Redescription. Colour. Cuticle brown to black; russet red elytra in some forms of A. minor and A. crypsis ; white to tan, lanceolate to blunt-ended setae (rounded setae) or scales (flattened setae) covering the dorsum (Figs. 1–8). Head. Anterior clypeal margin slightly reflexed and emarginate medially, with frontoclypeal suture usually distinct, fine, arcuate medially. Clypeal suture less distinct in A. crassa , A. ugandensis , and some A. minor (Figs. 28, 30, 36). Single setiferous protuberance (tubercle) on the frons adjacent to each eye (Figs. 24, 26, 28, 30, 32, 34, 36, 38); partial setiferous ocular canthus present. Setiferous punctures covering entire head; setae or scales directed posteriorly. Antennae in both sexes with 10 antennomeres (Fig. 9), the three-antennomere club slightly longer in males. Mouthparts (Figs. 13–20). Epipharynx: (Fig. 17) Bilobed, with a deep notch; stiff setae on the apical margin; lateral combs form a setal patch. Mandibles: (Figs. 15–16, 18) Asymmetrical, heavily sclerotised, posses dentate apicali and prosthecae; molar lobes large with rough ridges and mandibular brushes. Maxillae: (Figs. 19–20) palps with 3 palpomeres, lacini form oval lobes with stiff setae; each galea with five teeth. Labium: (Figs. 13–14) Labium, mentum, prementum, and submentum partly fused; palps with 3 palpomeres; ligula bilobed. Tentorium: following Nel & Scholtz (1990) the tentorium is in “group 2”. Pronotum. Anterior lateral margins crenulate and setiferous; surface covered by scaliferous or setiferous punctures (Figs. 54, 59, 64, 69, 74, 79, 84, 89), lateral margins with an oblique angle in the middle (Figs. 1–8), long fine setae on the periphery (view in lateral aspect), especially the anterior margin of A. minor , A. crypsis , and A. subfasciata . Absent in A. adspersa , A. rex , A. crassa , and A. ugandensis . Scutellum. Broadly triangular, almost rounded, either without scaliferous or setiferous punctures ( A. adspersa , A. crassa , A. rex , and A. ugandensis see Figs. 94–101) or with scaliferous or setiferous punctures ( A. crypsis , A. minor , and A. subfasciata , see Figs. 102–109). Elytra. Covered by fine lanceolate to blunt ended scales (Figs. 110–133); two to three bare areas at the base of the elytra for most species except some populations of A. minor . Elytra lacking distinct elytral stria or insterstria, or if present stria weakly developed. Humeral calli lacking setae or scales. Abdomen. Propygidium with medial longitudinal groove (or propygidial groove) (Fig. 12). Sternites with fine setae. Pygidium triangular and covered by scales (Figs. 134– 139, 142–149), or setae (Figs. 140–141). Legs. Protibia tridentate (Figs. 1–8, 11), basal tooth reduced, with straight, protarsal spur. Protarsal claws symmetrical, toothed medially and at base (Fig. 10). Male genitalia. Parameres simple and symmetrical (Figs. 150–173). The parameres of the male genitalia are quite similar among morphologically and geographically distinct species. This makes species level identifications based solely on the male genitalia unreliable.

Sexual dimorphism. Male and female Asthenopholis , unlike some other melolonthine scarabs, are not easily distinguished by their antennae and protibiae. However, within species, the relative width of the metafemora, metatibiae, metatibial corbulae, and metatibial spurs can be useful in separating males and females. This works especially well for the larger species ( A. adspersa , A. rex , A. crassa , and A. ugandensis ) and, to a lesser degree, for the smaller species ( A. crypsis , A. minor , and A. subfasciata ).

Propygidial groove. All species of Asthenopholis have a propygidial groove (Fig. 12). Crowson (1981) discusses this “median groove” as a mechanism that allows beetles to lock the elytra onto the abdominal sternites in order to protect their hind wings from abrasion and saturation. The configuration of this structure in Asthenopholis suggests the same function. The elytral apices have hooks that can lock them into the groove, as evidenced by many of the examined specimens.

Brenske (1898) included the propygidial groove in his description of A. transvaalensis , but made no mention of it in his generic description of the genus, nor in his brief description of A. minor . Arrow (1902) suggested its use as a distinctive generic character for recognizing Asthenopholis . He used this character again when describing the genus Stenopegylis and noted the superficial resemblance of the two genera with each other ( Arrow 1943).

The only other Afrotropical melolonthine genera, known to me, with propygidial grooves are Psilonychus Burmeister (see Péringuey 1904), Wernophylla Lacroix (see Lacroix 2001), and the Madagascan Leptolepis Ley and Tricholepis Blanchard (see Lacroix 1989).

Warner & Morón (1992) use a propygidial groove to help distinguish the New World Triodonyx Saylor from other subgenera of the diverse genus Phyllophaga Harris. Paulsen (2007) notes that both the Neartic Xenochodaeus Paulsen and Neochodaeus Nikolajev (Ochodaeidae) have propygidial grooves and uses it as a generic level character. Within the dung beetles Philips et al. (2002; 2004) includes the propygidial groove as a character for phylogenetic analyses of the Eucraniini and Scarabaeinae respectively. A morphological equivalent on the pygidium , i.e., a pygidial groove, is also found in the Neotropical tribe Eupariini (Aphodiinae) ( Smith & Skelley 2007).

Natural history and pest status. The larval and adult mouthparts (Figs. 13–20) of Asthenopholis species are well developed for plant feeding and both are capable of becoming agricultural pests under appropriate environmental conditions.

Petty (1977a, b) recorded the first outbreak of A. subfasciata on pineapple from August to October 1976 in the Eastern Cape of South Africa. The larvae caused severe damage by feeding on the roots and boring into the stumps of pineapple plants. Petty (1982, 1990, 1994, 2001) and Petty et al. (2002) conducted further studies on A. subfasciata and concluded that it was an important pest of pineapple in South Africa. Based on his work he found that adult A. subfasciata are active from November through January. First instar larvae are present in the soil in April/May, 2nd instars in May/June, and 3rd instars in October/November. Pupae occur in October/December. Most individuals have a 1-year life cycle, but a few take two years ( Petty et al. 2002), possibly as a result of completely developed adults remaining in the soil for another year.

The most successful chemical control was achieved when insecticides were sprayed to coincide with the adult beetle emergence and egg laying ( Petty 1976, 2001). However, since Eastern Cape pineapple growers (in South Africa) have been applying chlorpyriphos as a pre-plant soil treatment they have not had further outbreaks of A. subfasciata , or other white grub species (G. D. Petty, Agricultural Research Council, Institute for Tropical and Subtropical Crops, Bathurst, South Africa; personal communication 2007).

Williams (1985) records A. minor (as A. subfasciata ) to have a limited distribution in the Nokwane (Mhlume) and S.I.S. ( Swaziland Irrigation Scheme) sugarcane farms in Swaziland. Carnegie (1988) mentions A. minor and A. subfasciata as sugarcane pests in Swaziland and Emoyeni, KwaZulu– Natal. White grubs of A. subfasciata (Anonymous 1992) are reported from sugarcane fields from the Mhlume area (Vuvulane) in Swaziland. However, the present study establishes that these are misidentifications. Asthenopholis subfasciata does not occur in Swaziland or KwaZulu– Natal (i.e. Port Natal = Durban), save for a few old and questionable records. Asthenopholis minor is more likely to be a sporadic pest of sugarcane in these regions.

Larvae. Oberholzer (1959a, b) described the third instar larvae of A. subfasciata using specimens from the “Pineapple Research Station, Bathurst” suggesting an earlier infestation than the one reported by Petty (1977a, b). Smith et al. (1995) in a paper describing a variety of pineapple scarab pests redescribed A. subfasciata without referring to the Oberholzer (1959a, b) papers. No other Asthenopholis larvae have been described.

Soil preference. The worst outbreaks of the pineapple pest, A. subfasciata , occurred on red-sandy-loam soil ( Petty 1977a) with the following profile: 51.9% clay; 32% fine sand; 16% silt (G. D. Petty, Agricultural Research Council, Institute for Tropical and Subtropical Crops, Bathurst, South Africa; personal communication 2007). This suggests that the larvae prefer this soil type ( Petty 1990; 2001; Petty et al. 2002). Sweeney (1967: 40) claims that A. minor (as A. subfasciata ) is a localized species that occurs in heavy clay soils, or pockets of these soils in sandy fields. The localised distribution (Figs. 21–22) of some Asthenopholis species, e.g. A. adspersa , A. crypsis , and A. subfasciata also suggests, in part, preference for specific soil types. Other melolonthine grubs, such as Australian canegrubs (white grubs, e.g. Antitrogus parvulus Britton and Lepidiota negatoria Blackburn ) are known to be associated with specific soil types, while species from the same genus (i.e. Lepidiota crinita Brenske ) had no significant correlation with soil type ( Cherry & Allsopp 1991).

Diel activity. Many melolonthines are assumed to be crepuscular or nocturnal in their flight activity patterns. Direct (i.e. pairs mating during the day) (M. Way, SASR; personal communication 2008) and indirect evidence (i.e. no records from light traps) indicates that at least one species of Asthenopholis is diurnal (i.e. A. minor ) while A. crypsis is suspected to also be day active. Based on the material examined A. adspersa and A. subfasciata are nocturnal, and the diel activity for these species is unknown ( A. rex , A. crassa , A. ugandensis , and A. crypsis ).

Phenology. The known phenologies of Asthenopholis species are summarised in figures 174–180. Peak activity occurs in summer (October through December), with few or no records during winter. The activity of Asthenopholis subfasciata (Fig. 180) provides the best available estimate (based on 82 records for 211 males and 42 females) of a southern African Asthenopholis species seasonal abundance.

Biogeography. The known distribution of Asthenopholis species (Fig. 23) is undoubtedly biased by the low collecting intensity of leaf chafers in certain parts of southern and eastern Africa. Thus, additional country records or even species are expected in the future from Mozambique (e.g. range expansion for A. rex ), and probably from the highlands of eastern Zimbabwe and Malawi. Consequently, with this in mind their distribution can be classified as a typical cool highland and cool or wet coastline distribution. Two closely related dung beetle species show a similar pattern: Euoniticellus africanus (Harold) in South Africa and E. inaequalis (Reiche) in East Africa. Other relatives of Euoniticellus Janssens can be found on intervening highlands in eastern Zimbabwe, Malawi, and southern Tanzania ( Davis et al. 2008; A. L. V. Davis, Department of Zoology and Entomology, University of Pretoria, Pretoria, South Africa; personal communication 2009).

Tribal placement. Authors to consider the tribal placement of Asthenopholis were Brenske (1898) who placed the genus within “the Leucopholidarum” (= Leucopholini / Leucopholina) and Péringuey (1904) who included Asthenopholis , together with several genera ( Brachylepis Kolbe , Eulepida Kolbe , Hypopholis Erichson , Pegylidius Péringuey , and Pegylis Erichson ) in his “Group Leucopholides” (= Leucopholini / Leucopholina). Lacroix (2009) hosts a website where many African Melolonthinae genera are arranged into tribes, but these are intuitive groupings based on limited characters rather than a classification based upon a phylogenetic analysis. Lacroix’s (1989, 2008, 2009) African Leucopholini includes the following 13 genera: Afrolepis Decelle , Asthenopholis Brenske , Brachylepis Kolbe, Brysalepis Brenske , Camerunopholis Lacroix , Cochliotis Kolbe , Eulepidopsis Burgeon , Eulepida Kolbe , Lepidomela Kolbe , Pholidochris Kolbe , Pseudopholis Duvivier , Spaniolepis Kolbe , and Tanzanilepis Lacroix. Lacroix (1989) placed the following genera in the tribe Pegylini: Eupegylis Duvivier , Hypopholis Erichson , Pegylis Erichson , and Stenopegylis Arrow. Consequently , a tentative tribal placement of Asthenopholis based only on the above would be within the tribe Melolonthini Leach and subtribe Leucopholina Burmeister following Smith’s (2006) Scarabaeoidea classification. However, this placement awaits confirmation from a forthcoming phylogenetic analysis of the southern African Leucopholina (Harrison in preparation).