Metisella orientalis orientalis Aurivillius, 1925

Cock, Matthew J. W. & Congdon, T. Colin E., 2017, Observations on the Biology of Afrotropical Hesperiidae (Lepidoptera) with particular reference to Kenya. Part 11. Heteropterinae, Zootaxa 4226 (4), pp. 487-508 : 494-498

Metisella orientalis orientalis Aurivillius, 1925

Aurivillius (1925) gave the name orientalis to the 'race' of M. metis (Linnaeus) (a South African species) which occurs ‘in the whole of East Africa as far as Mt. Elgon’ ( Figure 7 ). It is treated as a valid species of Metisella by Evans (1937), who gave its distribution from the Central Highlands of Kenya through Uganda to Zaire, Cameroon, and Nigeria, and South through Tanzania to Malawi and Zimbabwe, in nine different infraspecific forms. Subsequently Evans (1938) described ssp. elgona from Mt. Elgon on the Kenya-Uganda border. Larsen (2009) clarified that Aurivillius’ treatment of the name orientalis should be considered an available name, not an unavailable infrasubspecific name, under the current rules of zoological nomenclature. De Jong (1976) illustrates the male genitalia from Kakamega Forest, western Kenya .

Three forms are recorded from Kenya ( Evans 1937): orientalis from the Central Highlands; theta Evans (wet season form of orientalis ) from Central Highlands and western Kenya ; and lamda Evans from Maungu, near Voi. In Tanzania, Evans (1937) recognised form zeta Evans from western Tanzania , kappa Evans from the Usambaras (south to Mozambique) ; and form lamda from northern Tanzania. Kielland (1990) states that M. orientalis is found on ‘practically every mountain with evergreen forest’ in Tanzania and suggests every mountain range has its own form of M. orientalis . This is probably at least partially true in Kenya too.

Evans distinguishes the wet season form theta as having the male hind wing underside brightly spotted, as are all females. A population which MJWC found in the South Nyambani Hills at 1650m seems distinct from others, having the hind wing upper side marginal spots heavily marked in dark orange. It is possible that several species are involved here, and a revision of the whole genus may be undertaken by R. de Jong. For the present, the name M. orientalis orientalis seems adequate for all Kenyan and Tanzanian material pending the assembly and critical analysis of good series of material from key localities, supported by evidence from biology, behaviour and molecular studies. Adults and early stages are normally uncommon, only the odd specimen or two being found at one time. However , TCEC found that it can be common at Mufindi, Tanzania, especially late January to March, along streams through the forest.

Food plants. MJWC reared this species three times in Kenya: a specimen from Kakamega Forest (88/17B) was collected on Cenchrus trachyphyllus (= Pennisetum trachyphyllum ), and in captivity accepted another Nairobi grass; another specimen was collected on Panicum trichocladum at Kisii (91/9) and in captivity fed on Panicum maximum ; and three specimens from the bottom of Thomson's Falls (90/125) were on a non-flowering grass which resembled (and could well have been) Cenchrus trachyphyllus . Accordingly , Larsen (1991) gave the food plants as ‘various grasses’ and included Pennisetum , based on MJWC’s record from C. trachyphyllus . At Mufindi , Tanzania, TCEC found this species on Festuca africana , but not on an adjacent Setaria sp.

Leaf shelters. Caterpillars made shelters from rolled grass leaves, but no details were noted.

Caterpillar. The penultimate instar caterpillar shown in Figure 8.1–2 has the head 1.4 x 1.6mm wide x high (n=2); dark black-brown, the frons brown or translucent, the clypeus brown; shiny, weakly rugose on epicrania; shiny smooth adfrontals and frons, with shallow transverse grooves on adfrontals and to a limited extent on the ventrolateral frons; adfrontal suture not easily distinguishable, frontal suture defined by a row of small pits; covered with inconspicuous dark setae; pronotum a narrow black transverse band; anal plate black, shiny; body blue green, a diffuse white subdorsal line bordering the dorsal line; a more sharply defined white dorsolateral line.

The final instar (Figure 8.3–4) measured 15mm when newly moulted and grows to at least 23mm. Head similar in shape and appearance to some Borbo spp. ( Baorini ); 1.8 x 2.4mm wide x high (n=4); rounded, relatively narrow, widest at stemmata, flattened at vertex; rugose; translucent dull matt green; broad black stripe from back of vertex anterolaterally to stemmata, narrower ventrally; posterior margin narrowly dark laterally and sometimes dorsally; one individual (91/9) had a small dark area on the epicrania adjacent to the top of the adfrontals; scattered short, fine, erect, pale setae. T1 translucent, unmarked, concolorous with body. Body translucent dull yellow-green; dorsal line darker, defined by a diffuse, pale, subdorsal line; stronger, white, dorsolateral line; anal plate rounded, shiny, green (not black as in previous instar); T2 with white anterior margin, joining the dorsolateral lines at each side; body with scattered, short, fine setae; legs concolorous; spiracles inconspicuous, white connected by a visible subcutaneous tracheal line; no wax glands. The fifth instar takes 13–16 days.

The caterpillars from Mufindi which TCEC reared are similar but not identical ( Figure 9 ). It can be seen that in the mature final instar caterpillar (Figure 9.2), the broad, black stripe on each epicranium is slightly narrower than Kenyan material, the subdorsal line on the body is double, the inner one being brighter and whiter; the posterior margin of the head is narrowly black (Figure 9.3) and there is a dark lateral spot on T1 which may be the spiracle (Figure 9.4). More material is needed to assess individual variation before assessing differences between populations.

Pupa. A pupa (Figure 10.2) was found in situ at Thomson's Falls, Nyahururu, Kenya (MJWC 90/125A) in the rolled distal part of a leaf which drooped where there was feeding basal to this; the pupa was formed head up in the shelter, with a flimsy girdle at the posterior part of the thorax, and the cremaster attached to a silk cross bar; no white waxy powder. The pupa ( Figure 10 ) is 21mm long, and similar to others of the genus; elongate with smoothly contoured 2mm frontal spike, which may be slightly upturned at apex, 1.3mm wide at the base; posterior end rounded; light, dull green or yellowish green; dorsal line dark, extending onto frontal spike; thin, diffuse white subdorsal line bordering dorsal line from thorax to a little short of end of abdomen; wider, stronger, white dorsolateral line from thorax to end of abdomen; traces of a broken, dark dorsolateral line on head, continuing laterally on thorax and along dorsum of wings, with a noticeable small spot on anterior margin A1 adjacent to the hind wing; A3–A7 traces of a double pale lateral line; spiracles all inconspicuous. The developing adult colour and wing markings are visible as the pupa matures. Pupal development takes 11-13 days, and adult emergence when noted was in the morning.

The pupa from Tanzania ( Figure 11 ) was a slightly brighter green, and the dark markings more contrasting; otherwise very similar.

Figures

FIGURE 7. Adult Metisella orientalis orientalis collected as penultimate instar caterpillar on Cenchrus trachyphyllus (unconfirmed plant identification), Thomson’s Falls, Nyahurura, Kenya, 29 Dec 1990; adult emerged and photographed 30 Jan 1990; MJWC 90 / 125 C. 1, upper side; 2, underside.

FIGURE 9. Final instar caterpillar of Metisella orientalis orientalis, collected on Festuca africana, Mufindi, Udzungwa Mountains, Tanzania [TCEC]. 1, dorsal view, 20 Mar 2004; 2, dorsal view, 20 Mar 2004; 3, prepupa, dorsal view, 23 Mar 2004; 4, detail of head of prepupa, anterior view, 23 Mar 2004.

FIGURE 10. Pupae of Metisella orientalis orientalis, Kenya [MJWC]. 1, collected as final instar caterpillar on Cenchrus trachyphyllus, Kakamega Forest, 26 Feb 1988; pupated 7 Mar; photographed 8 Mar 1988; adult 18 Mar; 21 mm; 88 / 17 B; 2, collected as pupa on Cenchrus trachyphyllus (unconfirmed plant identification), Thomson’s Falls, Nyahurura, Kenya, 29 Dec 1990; photographed 29 Dec; adult 10 Jan 1991; 21 mm; 90 / 125 A.

FIGURE 11. Pupa of Metisella orientalis orientalis, collected on Festuca africana, 26 Mar 2004, Mufindi, Udzungwa Mountains, Tanzania, dorsal view [TCEC].