Spialia zebra bifida Higgins, 1925

Cock, Matthew J. W., 2016, Observations on the biology of Afrotropical Hesperiidae (Lepidoptera) with particular reference to Kenya. Part 10. Pyrginae, Carcharodini, Zootaxa 4173 (4), pp. 301-350 : 332-336

Spialia zebra bifida Higgins, 1925

De Jong (1978) placed the next two species in the delagoae group, along with four other Afrotropical species ( Table 1 ). The nominate subspecies, S. z. zebra was described from Attock (= Campbellpore) and the Kala Chitta Range (=Chittar Pahar) in the Pakistan Himalayas (Butler 1888), and seems to be restricted to that area (Roberts 2001) . Kenya seems to be the headquarters of S. zebra bifida which Higgins (1925) described from Nairobi, although its range extends to all five neighbouring countries and Yemen.

Records from Kenya extend from the north-west, through western, central, and southern Kenya to the coast. It does not seem to be rare, particularly as caterpillars on the known food plants.

I have rarely seen the adult of this species ( Figure 26 ) in the field, but along the Nairobi– Mombasa Road the caterpillars are common from close to Nairobi (50 km) to the coast. I have also reared it from Kakamega; thus, although I think of this as a dryland species, it is in fact rather more adaptable and widespread.

Food plants. Van Someren (1974) records Melhania ovata and M. velutina for East Africa , while Sevastopulo (1974, 1975) lists Melhania sp. Sevastopulo (unpublished) reared this species at Mombasa, but did not record the food plant; however, he does list Melhania sp. as a food plant (after Van Someren), and gives the same food plant genus in his own publications, so his own records were most probably also from a Melhania sp. Kielland (1990) lists Melhania , whereas Larsen (1991) notes Melhania , Dombeya , and ‘other plants’, Dombeya based on my records (below)

I regard Melhania spp. as the typical food plant of this species, and I have found caterpillars on M. velutina from Machakos to the Coast on more than a dozen occasions, and on M. taylori (this unresolved name may be a synonym of M. rotundata ) at Diani Beach. However, further collecting has shown that at least two other Malvaceae , Hermannia exappendiculata (Diani Beach, Kibwezi Forest) and? Dombeya burgessiae (Kakamega) , are also used.

Ovum. Ova are laid on the leaf under surface, close to the edge, often on small leaves before they are fully open. The ovum shown in Figure 27 was collected at Kibwezi Forest in association with caterpillars of S. zebra bifida , but there is scope for confusion as S. kituina feeds on the same food plant at the same locality. Conversely, what I have interpreted as the ovum of S. kituina was collected in association with caterpillars of that species at Diani Beach, but S. zebra bifida also occurs on the same food plant there. The two ova are quite similar, but whereas that treated as S. kituina ( Figure 2 ) has six ridges around the micropyle and 18 around the base, this ovum has five ridges around the micropyle and about 22 ridges around the base; further the ovum of S. kituina is relative flattened dorso-ventrally, whereas that of S. zebra bifida is deeper and more globular.

Leaf shelters. On Melhania spp. the leaf shelters are formed by folding the leaf up along the mid-rib, small caterpillars usually in small leaves and large caterpillars in larger ones. I have noted that after rain the shelters may be full of water. The caterpillars in captivity often develop slowly, and I suspect in the field, they go into diapause during the dry season. At this time Melhania velutina loose many leaves, but the attachments of those used as a shelter by S. zebra are strengthened by the caterpillar with dark red-brown silk along the petiole, to ensure they are retained. On Dombeya burgessiae , one caterpillar had pulled the terminal leaves of a sucker plant together, and another had made a shelter between two leaves. One field collected pupa was in a shelter made by folding over a leaf edge of M. velutina , and within the shelter, the pupa was formed within a tough cocoon of grey silk (MJWC 88/74A).

Caterpillar. T he caterpillars mostly feed by skeletonising the leaf upper surface, often protected where the sides of the leaf are drawn together in the leaf shelter. Only the largest caterpillars consume the full thickness of the leaves of M. velutina .

The following description, based on a 13mm final instar caterpillar (MJWC 88/48) was expanded with recent microscopic observations of remains of early stages. Head 2.4 x 2.4mm wide x high (range 2.24–2.55 x 2.24– 2.55mm; n=6); dark brown, shiny, reticulate-rugose; rounded, slightly indent at vertex; face covered with short, erect, aciculate setae, which are slightly shorter, darker and less dense to form an ‘eye-spot’ centrally on each epicranium; a similar spot above the stemmata is often present; similar setae on adfrontals and frons are semirecumbent; laterally longer, dark brown, erect, simple setae; similar setae posteriorly, but pale to brown in colour; scattered pale, long, simple setae from stemmata across ventral part of face. T1 pronotum divided by a groove into a narrow more or less black section along the posterior margin, and a wider dark brown to black section occupying about 2/3 of segment anterior to this, with white dorsal and dorsolateral patches, wider on the anterior margin; scattered long, pale, erect, simple setae and denser, shorter, pale, erect setae with a clubbed or button-like apex; T1 legs dark brown. Body dull blue-green, covered with sparse short, white, simple setae on white dot bases; darker dorsal line; yellowish dorsolateral line; weak lateral line through spiracles; A8 with white subcutaneous lateral patch with conspicuous dark spiracle; other spiracles small, dark; prolegs concolorous; legs T2, T3 transparent pale brown; body covered with short, pale, erect setae, bifurcate just before apex.

The penultimate instar caterpillar is similar to the final instar, but the dark eye spots are less distinct; head 1.9 x 2.0mm wide x high (n=3). An n-2 instar caterpillar was noted to be similar, but the setae on the head were even shorter, making the eye-spots less distinct; head 1.6 x 1.7mm wide x high (n=4).

The eye-spot effect on the head of the caterpillar ( Figure 28 ), created by the short dark aciculate setae which are white on the rest of the face, are distinctive for this species. The upper spot is most conspicuous, but a lower spot may be present. One caterpillar I reared had these spots much less conspicuous, although the underlying pattern is still evident (MJWC 90/115C; Figure 26.6–7). Most caterpillars in captivity seem to develop slowly, some instars taking up to a month. Caterpillars collected from vigorous plants in the rainy season, and fed good quality fresh leaves develop more rapidly; for example, one from Kibwezi Forest took 5, 10 and 15 days for the last three instars.

Pupa. A pupa reared from a caterpillar collected from Melhania velutina at Diani Beach ( MJWC 90 /108A) was 13mm long, with a short blunt cremaster, and the colouring four days after pupation and ten days before emergence (Figure 29.1–2) was light whitish green apart from the conspicuous protuberant black T1 spiracle, dark spiracles, faint dot below abdominal spiracles and a dark line vertically through the eye. Another pupa reared from the same food plant (junction of Mombasa and Machakos Roads, MJWC 89 /66) was examined 8 days after pupation and five days before emergence. Dorsally grey; abdomen ventrally light green; wing cases with costal half white, remainder grey; other appendages light grey; spiracle T1 conspicuous, protuberant, matt black; other spiracles small, black, inconspicuous. Just before emergence, another pupa reared from a caterpillar collected at Diani Beach ( MJWC 90 /115C) generally dark dorsally and on the head and thorax, the abdomen pale ventrally, and the wing markings clearly visible (Figure 29.3). These three observations indicate a steady darkening during pupal development, as the adult colouring becomes more pronounced and hence visible through the translucent pupal cuticle.

However, a newly formed pupa from a caterpillar collected on Dombeya burgessiae (MJWC 89/47 A) was predominantly black, except ventrally on the abdomen and the anterior margins of the abdominal segments which were pale. The contrast between the termen of the wing cases and the abdomen was striking. The spiracle T1 was matt black and there was a shiny, black, vertical line through the eye. Three eclosed pupae from Kakamega were dark brown, whereas those from Diani Beach were very pale brown.

Spiracle T 1 is rounded semicircle in shape, the flat edge facing anteriorly; the posterior edge was higher with a vertical wall-like edge, the basal half smooth and brown, the distal half bulbous and dark brown; the upper surface similarly dark brown; spiracles measured 0.45mm dorso-ventrally, 0.27mm wide and 0.25mm high (n=2). Pupae had scattered pale, simple setae, semi-recumbent on the abdomen, and erect, but curved distally, on the thorax and head; a light bloom of white waxy powder, mainly on the abdomen. There are very small, inconspicuous, oval, brown or pale brown plaques anterior and dorsal to the spiracles A 2 – A 8, and posterior and ventral to those of A 4 – A7, but about 25% had the upper row significantly displaced to a subdorsal position. Figure 29 shows individuals with the plaques in the former arrangement. The two arrangements occurred equally frequently in males and females. The pupal stage at Nairobi lasts 13.3 days (range 11–19, n=15); in contrast Sevastopulo (unpublished) recorded just seven days at Mombasa.

Natural enemies. A larval-pupal tachinid fly, Thecocarcelia latifrons , attacks S. zebra . I have reared this tachinid from the Nairobi-Mombasa Road at the junction with the Machakos Road. The fly puparium can be found within the host pupa (Figure 29.4), or within the pupal shelter. I have observed a puparium formed 3 days after the host pupa, and the fly emerged 12 days after that, and I have also noted a fly emerge 22 days after the host pupated. This tachinid also attacks S. diomus , S. ferax , S. spio and Gomalia elma (see species accounts).

The caterpillars are also attacked by an unidentified ichneumonid endoparasitoid; it took 17 days to emerge from the cocoon.

Figures

FIGURE 2. Three views of an ovum of Spialia kituina, collected on Hermannia exappendiculata, Diana Beach, 12 Dec 1990; MJWC 90 / 109. 1, dorsal view; 2, dorsolateral view; 3, lateral view.

FIGURE 27. Probably ovum of Spialia zebra bifida, collected on Hermannia sp., Kibwezi Forest, 7 Mar 1991; died; collected in association with caterpillars of S. zebra, but S. kituina also feeds on this host at this locality; MJWC 91 / 11. 1, dorsolateral view when relatively fresh; photographed 18 Mar; 2, dorsal view when dead; the caterpillar appears to have eaten part of the dorsal shell leaving the ridges and the black head is partially visible; photographed 28 Mar.

FIGURE 28. Final instar caterpillars of Spialia zebra bifida, Kenya. 1, collected as n- 2 premoult on M.? velutina, Kibwezi, 10 Dec 1989; moulted to final instar 27 Dec; photographed 1 Jan 1990; pupated 11 Jan; MJWC 89 / 95. 2, collected as final instar on Dombeya burgessiae, Kakamega 17 May 1989; photographed 17 May 1989; pupated 24 May; MJWC 89 / 47 A. 3, collected as final instar caterpillar on Melhania? velutina, Ndara, 1 Apr 1989; photographed 2 Apr; pupated 11 Apr; MJWC 89 / 27. 4, collected as penultimate instar premoult on M. velutina, Kibwezi Forest, 29 Jul 2001; moulted to final instar 31 Jul; photographed 1 Aug; pupated 20 Aug; 15 mm; MJWC 01 / 201 A. 5, collected as final instar on Melhania velutina, Diani Beach 12 Dec 1990; photographed 13 Dec; pupated 14 Dec; MJWC 90 / 108 A. 6 – 7, collected as final instar on Melhania taylori, Diani Beach 13 Dec 1990; moulted to final instar 11 Jan 1991; photographed 27 Jan; pupated 24 Feb; MJWC 90 / 115 C; 6, dorsolateral view; 7, detail of head, anterior view.

FIGURE 29. Pupae and parasitoid of Spialia zebra bifida, Kenya. 1, dorsolateral view; collected as caterpillar on Melhania taylori, Diani Beach, 12 Dec 1990; pupated 14 Dec; photographed 16 Dec; adult 26 Dec; 13 mm; MJWC 90 / 108 A. 2, ventrolateral view; as # 1 but photographed 20 Dec; MJWC 90 / 108 A. 3, lateral view; collected as # 1; 13 Dec 1990; pupated 13 Dec; photographed 24 Dec; adult 25 Dec; 11 mm; MJWC 90 / 115 C. 4, dorsolateral view with partially exposed view of puparium of Thecocarcelia latifrons; collected as caterpillar on M. velutina, Nairobi-Mombasa Road at the junction with the Machakos Road, 24 Sep 1989; pupated 9 Oct; puparium visible 18 Oct; adult T. latifrons 1 Nov; MJWC 89 / 65 A.

FIGURE 26. 1 – 2, adult male of Spialia zebra bifida, collected as caterpillar on Melhania velutina, Nairobi-Mombasa Road at the junction with the Machakos Road, 24 Sep 1989; adult 14 Oct; MJWC 89 / 66 B.