Basilepta subcostata (Jacoby, 1889)

Prathapan, Kaniyarikkal D., Poorani, Janakiraman, Kumari, S. Amritha, Anuradha, C., Balakrishnan Padmanaban, & Thanigairaj, Ramalingam, 2019, Species composition and diagnoses of leaf- and fruit-scarring beetles (Coleoptera, Chrysomelidae) infesting bananas and plantains (Zingiberales, Musaceae) in the Indian subcontinent, Deutsche Entomologische Zeitschrift 66 (2), pp. 179-202 : 179

Basilepta subcostata (Jacoby, 1889) Figs 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8

Nodostoma subcostatum Jacoby, 1889: Jacoby 1889: 164; Jacoby 1908: 334.

Nodostoma cyanipenne : Lefèvre 1893: 120; Kimoto and Gressitt 1982: 51 (synonymy).

Basilepta subcostatum : Kimoto 1967: 69; Medvedev 1990: 8-9; Chûjô 1964: 268-269.

Basilepta subcostata : Kimoto and Gressitt 1982: 51; Sprecher-Uebersax 1997: 144; Medvedev and Sprecher-Uebersax 1999: 288; Kimoto 2001: 27; Medvedev 2001: 608; Kimoto 2005: 31-32; Moseyko and Sprecher-Uebersax 2010: 639.

Material examined.

Type material: syntype female, "SYNTYPE (blue bordered circular label)/ Bhamὀ, Birmania, Fea, VII.1886/ Jacoby Coll. 1909-28a/ Nodostoma subcostatum Jac./ abdomen missing, S.L. Shute 1976/NHMUK014016383" (BMNH). Other material: 64016/Birmah, Momeit/Doherty/Fry Coll. 1905-100, 1 ex.; Tharrawaddy, Burma/ Andrewes Bequest 1922-221/ Nodostoma subcostatum Jac., 1 male with genitalia glued to the same card; Assam, Sudiya/ Doherty/ Fry Coll. 1905-100, 1 male; Assam, Patkai Mts./ Doherty/ Fry Coll. 1905-100/ Jacoby det., 1 ex; Thailand, Lot 1830, Nakhonratchasima, June 15, 1912/24/To B.M. List 153.10/ C.I.E. Coll. A1720/ Pres. By Com. Inst. Ent. B.M.1967-2, 2ex. (BMNH); S.INDIA, Mysore, Vittal 1964, Arecanut Res. Stn., on banana/ C.I.E. Coll. No.19658, 2 ex; Deccan/ 67.56, 1 ex; NEPAL: Rampur, 14.vii.1981, Ex. Banana, 6 ex; NEPAL: Dhunibesi, 22.vi.65, Banana, Dept. Agric. C.I.E. A.573, Col.161/ Pres. By Com. Inst. Ent. B.M. 1966-22, 2 females and 2 unsexed; 61647/ Doherty/ Assam, Patkai Mts/ Fry Coll. 1905-100, 4 ex; Bacan, N. India/ 67.56, 3 ex.; Calcutta / Atkinson Coll. 92-3, 2 ex; Doherty/ Tenesserim, Mergui/ Fry Coll. 1905-100; W. Almora Divn., Kumaon, UP, Aug. 1917, HGC/ E8/ H.G. Champion Coll. B.M. 1953-156, 4 ex; Lansdowne Division, UP, India, F.W.C./ H.G. Champion Coll. B.M. 1953-156, 1 ex.; Ind./ Baly Coll., 1 ex.; Khasis/ Coll. Kraatz/ Pres. by Imp. Inst. Ent. BM 1938-351/ Nodostoma occipitale Jac., Det. G.E. Bryant, 1 ex. (BMNH). India: Assam: 7 ♂ and 5 ♀ Balipara 74 m msl/ 26°49'56"N, 92°46'41.1"E /17.v.2019/K D Prathapan Coll.; 3 ♂ Jorhat /19-22.xi.2007/ Prathapan K D Coll.; 4 ♂ and 10 ♀, Assam: Dergaon, 26°42'01.00"N, 093°54'01.26"E /2.x.2018, R. Thanigairaj; Assam: 2 ♂, 2 ♀ Nameri Nat. Park 85 m msl/ 26°55'27.4"N, 92°49'38.9"E /17.v.2019/ K D Prathapan Coll.; Assam: 17 ♂, 13 ♀ and 7 unsexed, Tezpur 72 m msl/ 26°37'33.4"N, 92°48'41.5"E /19.v.2019/ K D Prathapan Coll.;. 25 ♂ and 14 ♀, Assam: Kaziranga, Kohora 70 m msl/ 26°35'29.6"N, 93°23'56.1"E /18.v.2019/ K D Prathapan Coll./Ex Banana; 2 ♂ same data, except Host Canna sp.; Meghalaya: 11 ♂, 13 ♀, Barapani/ 25°41'17.6"N, 91°55'5.1"E /5.vi.2013 993 m/Prathapan K D Coll./Ex. Banana; 3 ♂, 1 ♀, Meghalaya: Nongpoh 587 m msl/ 25°50'34.4"N, 91°52'34.4"E /22.v.2019/ K D Prathapan Coll.; 1 ♂, 6 ♀ Meghalaya: Cherrapunjee 1426 m msl/ 25°17'11.0"N, 91°43'07.8"E /21.v.2019/ K D Prathapan Coll.; 3 ♂, 3 ♀ Meghalaya: Umroi/2.xii.2007/Prathapan K D Coll.; 4 ex, Meghalaya: Jorabat, 04.x.2018, 26°04'59.52"N, 091°52'36.59"E, R.Thanigairaj; Meghalaya: 2 ex, Umiam/19.vii.2019/D. M. Firake/Ex ginger; 3 ♂ and 10 ♀, West Bengal: Cooch Behar, x.2016, B. Padmanaban; Uttar Pradesh: 4 ♂, 9 ♀ Faizabad Dist, 27°37'06.96"N, 081°36'29.54"E, 12.xi.2018, J. Poorani; Bihar: 6 ♂ and 1 ♀ Bhagalpur, 6.iii.2016, B. Padmanaban; Bihar: Falka, 11-12.x.2017, B. Padmanaban; Odisha: 4 ex, Bhubaneshwar, 29.v.2015, Sangeetha.

Generic diagnosis.

Body oblong; head mildly sulcate above eyes; antennae filiform or distal antennomeres widened; pronotum wider than long, widest posteriorly, lateral margins often angulate; anterior margin of proepisternum concave; legs long, all femora dilated, minutely dentate ventrally, tibia longitudinally sulcate with a sharp ridge along dorsal side; intermediate and posterior tibiae emarginated preapically; metatibia with a pair of short apical spines; prosternum broader than long. Claws appendiculate; bursa sclerites present in female genitalia.

Related species.

Basilepta makiharai Kimoto, described from Nepal, is stated to "resemble B. subcostata in having the elytron with humeral ridge but differs by its shorter body length and in having the surface of vertex finely shagreened" ( Kimoto 2001: 26). It is generally pitchy black to dark reddish brown with entirely yellowish-brown antenna. Basilepta viridipennis (Motschulsky), another species widely distributed in Southern Asia and erroneously reported as the banana fruit-scarring beetle from India and Bangladesh, is also externally similar to B. subcostata , but its antenna is almost fully blackish except for the first four antennomeres and the posterolateral callosity of pronotum does not project beyond lateral margin, and hence, the posterolateral corners of pronotum are obtuse and not angulate as in B. subcostata . Besides, the elytra are metallic green to violaceous and shinier and lack a distinct lateral costa.

Nodostoma obscurum Jacoby, 1908 and Basilepta sakaii Takizawa, 1987 were listed as synonyms of B. subcostata in the catalogue of Nepalese Chrysomelidae by Medvedev and Sprecher-Uebersax (1997: 288), but they did not mark it as a new synonymy. This appears to be incorrect because the type of N. obscurum is not even morphologically similar to N. subcostatum , whereas B. sakaii is a smaller insect according to the description (Alexey Moseyko, personal communication).

Description.

Length 2.34-3.00 mm, width 1.36-1.86 mm, 1.6 –1.7× longer than broad. Body ( Fig. 1 a–c ) oblong ovate, shiny. Colour highly variable from red-brown to dark blue, black, or their mixtures without any spots, stripes or maculations; head entirely red-brown to tinted black except vertex red-brown, palpomeres light yellow to brown, some specimens with apex of last palpomere black; basal 4-6 antennomeres light brown and rest gradually turning piceous to black; colour of pronotum and elytra varies from red-brown or dark blue to shiny black, pronotum concolorous with elytra or not, general color of legs red-brown to dark brown or testaceous, tibia distally and tarsomeres darker.

Three major color morphs and their intermediates were commonly observed:

Head and pronotum red-brown; elytra blue, blue-black, dark green, or black; all ventrites dark (Fig. 1a). A syntype, images of which were made available by the Museum of Comparative Zoology (http://140.247.96.247/mcz/Species_record.php?id=9291), belongs to this category.

Entirely red-brown, except distal antennomeres, legs and palpi piceous to black (Fig. 1c);

Entirely dark blue, blue-black, dark green, or black (Figs 1b, 2), except head medially red-brown; metasternum and abdominal ventrites piceous to black; all entirely dark variants observed were females.

Head ( Fig. 3a, b ) distinctly punctured with impunctate areas on vertex and frons; punctures bold, slightly smaller than those on pronotum. Coronal suture weak but evident. Supraorbital pore adjacent to dorsal margin of eye, rounded, with a long seta. Orbital sulcus with deep, bold punctures. Frons hardly differentiated from vertex, supra frontal sulcus weak. Frons with a few bold punctures, impunctate medially. Antennal calli trapezoidal, raised; supracallinal sulcus well developed with a few bold punctures. Clypeus forms narrow transverse band with strongly concave anterior margin; frontoclypeal suture with a few small punctures. Labrum broader than long, with a pair of broadly placed setose punctures in middle and a pair of setae anterolaterally; anterior margin with thick short setae on either side of middle, apical margin emarginate medially. Antennae hardly extend up to middle of elytra; first antennomere thick, longer than second; second antennomere thinner than first, thicker than 3rd and 4th separately; 5th onwards antennomeres progressively thicker; basal four antennomeres smooth, shiny, sparsely setose; distal seven thickly covered with short pointed setae, proportion of antennomeres as follows: 1: 0.80: 1.13: 1.33: 1.27: 1.20: 1.20: 1.27: 1.20: 1.13: 1.33.

Compound eyes with inner margin feebly emarginate, transverse diameter about 1.4 –1.5× vertical. Distance between eyes 1.8 × distance between antennal sockets, shortest distance between compound eye to adjacent antennal socket about 3.5 × distance between antennal sockets. Mandibles with two large denticles; maxillary palpi three-segmented excluding palpifer; last palpomere longest, penultimate palpomere less than half length of last palpomere. Labial palpi with three palpomeres, excluding palpiger, first palpomere being shortest and last longest.

Pronotum ( Fig. 3c, d ) about 1.6 × broader than long, posteriorly 1.6 –1.7× wider than anteriorly, somewhat trapeziform in outline, narrowed anteriorly, with posterolateral callosity laterally projecting beyond lateral margin, hence posterolateral corners appear sharply angulate, lateral margins angulate at posterior one-third presenting octagonal appearance, densely punctate, punctures larger than those on head and smaller than those on elytra, posterior margin gently lobed in middle, anterior sulcus and posterior sulcus distinct with a row of punctures, posterior sulcus deeper than anterior. Scutellum wider than long, broadly rounded posteriorly, sparsely and minutely punctate. Elytra 1.2 × longer than wide, punctate striate, punctation weaker towards apex, punctures regular post medially with 10 striae; partially confused and semiregular in anterior half of elytra due to incomplete or broken striae; distance between punctures in a row less than distance between adjacent rows; extreme lateral row of elytral punctures regular, complete, extending up to apex; second row merged with first row from anterior one-fourth to middle of elytra; third row arising from humerus extending up to apex of elytra; interstice between 2nd and 3rd lateral rows distinctly costate, extending as far as middle of elytra or beyond, costa variable in prominence, strongly convex and sinuate in the syntype female ( Fig. 2b ) (BMNH, examined), but only moderately prominent in most of the Indian material examined. Humeral calli well developed, post basal depression shallow but distinct; basal calli distinct, vary in prominence. Elytral apex narrowly convex. Epipleura outwardly oblique with sparse and fine punctures, narrowing beyond proximal one-third, hardly reaching elytral apex.

Prosternum broader than long, broader posteriorly than anteriorly, with bold punctures, posterior margin straight; mesosternum nearly twice as broad as long with a few punctures smaller than those on prosternum. Proepisternum depressed; hypomeron with bold punctures. Legs long; all femora dilated, minutely dentate ventrally beyond middle ( Fig. 3e, f ); tibia ( Fig. 3f ) with eight sharp carinae, variable in prominence: three each dorsally and ventrally, one each on either side laterally. Tarsomeres ventrally fringed with diverse forms of setae, basitarsomere with closely arranged capitate setae bordered by long pointed setae in males and only pointed setae in females, second tarsomere ventrally with pointed setae, bilobed third tarsomere with triangular or inverted arrowhead-shaped setae ventrally.

Ventrites sparsely punctate, pubescent; first ventrite medially longer than following two combined, ventrites 3 and 4 subequal, shorter than 2 and 5 separately which are subequal, last ventrite hardly sexually dimorphic, last tergite without longitudinal groove medially.

Male genitalia: aedeagus in lateral view ( Fig. 4a, c, e, h, k, m, n, o ) sharply bent almost at right angle near base of aedeagus proper, apical portion acutely narrowed and slightly recurved dorsally; in ventral view ( Fig. 4b, d, f, g, i, j, l ), depressed along ventral surface, apex narrowed forming obtuse denticle; apical opening wide, partially covered by a lamina with a pair of sclerotized stripes fused basally and joining dorsal surface. Tegmen ( Fig. 4q ) flat, membranous, lightly sclerotized, bilobed distally, proximally with a pair of arms which turn narrowed and encircle base of aedeagus proper. Spiculum gastrale (second spiculum of Jolivet and Verma 2008) Y-shaped, sclerotized. Tergite VIII semicircular with spindle-shaped sclerotization on either side, with short setae apically. Spiculum reclictum (sensu Slipinski and Escalona 2013) spoon-shaped, distally dilated ( Fig. 4p ).

Endophallus ( Fig. 5a ) long, membranous, tubular, about 3.7 –3.9× longer than aedeagus proper; with three distinct regions: basal phallomere (BP), median phallomere (MP), and apical phallomere (AP); basal phallomere ( Fig. 5b ) very short with a lateral lobe on either side, followed by two inwardly curved central sclerites (CS) dorsally; median phallomere ( Fig. 5c ) longest, tubular, with setae or hair like spicules, a few circular spicules present near apical region; apical phallomere ( Fig. 5d ) much wider than other two regions, asymmetrical, with spicules varying in shape such as triangular, angular, oval; apical region proximally with three minute lobes facing median phallomere, apex with large lateral lobes and several smaller lobes medially.

Female genitalia ( Fig. 6 ) with spermathecal capsule sickle-shaped ( Fig. 6a, b ), proximal portion very short, constricted medially, dumbbell-shaped where spermathecal duct and spermathecal gland join side by side, distal portion sickle-shaped, sharply curved, subacutely narrowed towards distal end; spermathecal gland long and tubular, length of spermathecal capsule 7.7 × its maximum width. Bursa copulatrix ( Fig. 6c ) sac like, longer than wide, with a long bursa sclerite (BS) on either side, spermathecal duct joins bursa copulatrix between these sclerites, median oviduct attached on the other side of bursa copulatrix. Ovipositor ( Fig. 6d ) elongate, sclerotized distally, with almost 10-16 long setae, stylus absent; 8th sternite and 8th tergite fused laterally to form a membranous cylinder with mild sclerotizations laterally ( Fig. 6f ); 8th sternite with a long tignum sensu Konstantinov, 1998 (spiculum ventrale sensu Slipinski & Escalona, 2013) longer than ovipositor ( Fig. 6e ); collateral gland (CoG) present ( Fig. 6g ).

Distribution.

India [Karnataka (new record); Delhi ( Batra 1952); Uttarakhand; Uttar Pradesh; Bihar; Odisha; West Bengal; Sikkim; Assam; Manipur; Meghalaya]. Bangladesh. Myanmar, Thailand, Laos, Cambodia ( Kimoto and Gressitt 1982; Vansilalom 2016); Nepal ( Medvedev 1990; Sprecher-Uebersax 1997; Kimoto 2001). A distribution map is available at this link: https://www.google.com/maps/d/edit?hl=en&mid=1QgHVswL3eaPJ2soJ16_R5BTkIu8mRM6z&ll=23.692266951458954%2C78.67937627596257&z=6.

Host plants.

Musa spp. ( Musa sapientum , M. acuminata ; Musaceae , Zingiberales ) are principal hosts. Beetles were observed feeding on ginger ( Zingiber officinale Roscoe; Zingiberaceae , Zingiberales ) in Meghalaya (D.M. Firake, personal communication). In Assam, northeastern India, adult beetles were observed feeding on Canna indica L. ( Cannaceae , Zingiberales ) and turmeric ( Curcuma longa L., Zingiberaceae ) and characteristic feeding marks were observed on the latter. This is the first documentation of other hosts of B. subcostata besides banana. Adults were also found to be resting on taro ( Colocasia sp., Araceae , Arales ) (unpublished data).

Bioecology.

The adult beetles are most active during the monsoon and post-monsoon seasons and summer. They are nocturnal and usually found hiding inside the leaf whorls and come out only when disturbed. They feed on the young unfurled leaves ( Fig. 7a ), leaf petioles ( Fig. 7d, e ), and stems of banana, and the emerging leaves ( Fig. 7b, c ) are badly scarred. Feeding damage was also observed on flowers ( Fig. 7f ) and bracts ( Fig. 7g ), as well as young, developing fruits ( Fig. 7h, i ). For more images of the damage symptoms on cultivated banana, see the website of ICAR-National Research Centre for Banana (2019). In severe cases, the developing bunches and fruits ( Fig. 7 j–l ) are so badly scarred that they lose their market value.

Eggs are laid in the soil and the larvae feed on the roots of grasses and other weeds. Pupation takes place in the soil. Emerging adults feed on young leaves and fruits. Adults hibernate during winter. Seasonal incidence and population dynamics of fruit scarring beetles have been studied from some parts of India, including Assam ( Mishra et al. 2015) and Bihar ( Ahmad et al. 2010; Sah et al. 2018).

Pest status.

Mukherjee et al. (2006) reported that meteorological factors accounted for about 85% of the beetle incidence in Bihar (India) and minimum temperature and maximum relative humidity had a positive and significant effect on scarring beetle populations. Though damage due to scarring beetles is believed to be mainly cosmetic, the fruit quality is also badly affected. Zahan et al. (2001) and Sah et al. (2018) reported that scarring beetle infestation significantly delayed fruit ripening, reduced the fruit weight, and adversely affected the skin colour and thickness of fruits and the taste and smell of the pulp. This damage considerably affects the consumption value.

Natural enemies.

In Uttar Pradesh, North India, adults of the predatory beetle, Paederus fuscipes Curtis ( Coleoptera , Staphylinidae ), were found to be commonly associated with B. subcostata . Natural epizootics of entomofungal pathogens, such as Beauveria bassiana , are commonly observed on B. subcostata in the northeastern region of India ( Fig. 8 ) and exert some control in the post-monsoon months.

Figures

Figure 1. Basilepta subcostata (Jacoby). a-c. Habitus, dorsal: a. Nominate form, male; b. Female; c. Rufous form, male; d. Male, lateral view; e. Female, lateral view.

Figure 2. Syntype (female) of Basilepta subcostata (Jacoby) (BMNH). a. Dorsal view; b. Lateral view.

Figure 3. Basilepta subcostata (Jacoby). a. Head, dorsal view, male; b. Head, dorsal view, female; c. Pronotum, male; d. Pronotum, female; e. Middle leg; f. Hind leg.

Figure 4. Male genitalia of different populations of Basilepta subcostata (Jacoby). a, c, e, h, k, m-o. Aedeagus, lateral view; b, d, f, g, i, j, l. Apex of aedeagus, ventral view; p. Male: tergite VIII, sternite VIII and IX; q. Male genitalia, tegmen.

Figure 5. Endophallus of Basilepta subcostata (Jacoby). a. Endophallus completely everted, lateral view; b. Basal phallomere and central sclerite, dorsal view; c. Median phallomere, lateral view; d. Apical phallomere, dorsolateral view. Abbreviations: BP = Basal phallomere; MP = Median Phallomere; AP = Apical phallomere; CS = Central Sclerite.

Figure 6. Female genitalia of Basilepta subcostata (Jacoby). a, b. Spermatheca; c. Bursa copulatrix; d. Ovipositor; e. Eighth sternite and tignum; f. Eighth sternite and 8 th ventrite along with tignum; g. Female genitalia. Abbreviations: SpG = spermathecal gland; SpC = spermathecal capsule; SpD = spermathecal duct; MdO = median oviduct; BC = Bursa copulatrix; BS = bursa sclerite; Vg = vagina; CoG = collateral gland; Tg = tignum; ovi = ovipositor.

Figure 7. Damage caused by B. subcostata (Jacoby) on banana. a. Leaf whorl showing scarring damage; b. Scars on spindle leaf; c. Scars on leaf; d, e. Scarring on leaf petiole; f. Flower damage; g. Bract damage; h-i. Damage on young fruits and emerging bunch; j-l. Fruit damage.

Figure 8. Naturally occurring epizootic of fungal pathogen, Beauveria bassiana on Basilepta subcostata.