Borbo fatuellus fatuellus Hopffer, 1855

Cock, Matthew J. W. & Congdon, Colin E., 2012, Observations on the biology of Afrotropical Hesperiidae (Lepidoptera) principally from Kenya. Part 4. Hesperiinae: Aeromachini and Baorini, Zootaxa 3438, pp. 1-42 : 21-23

Borbo fatuellus fatuellus Hopffer, 1855 ( Figures 17–18 )

Subspecies fatuellus occurs throughout sub-Saharan Africa and in Yemen, and additional subspecies have been described from São Thomé and the Comoros ( Evans 1937a, Larsen 1984). A form with grey scaling on the UNH (cinerea Holland) has been associated with the dry season in eastern and southern Africa ( Evans 1937a) and both forms are common in Kenya. Van Someren (1939) reports B. fatuellus as fairly numerous in the grass and bush along the forest margins from 4,500–6,000 ft. (1370–1830 m) in the Chyulu Hills, and it is not uncommon in the Makardara Forest ( Sevastopulo 1974). I consider it an occasional but widespread species of open forest throughout Kenya. TCEC has found it mainly in woodland in Tanzania, but extending into open areas in forest.

Adult behaviour

Adults settle low on grasses and shrubs when they are easily caught ( Dickson & Kroon 1978). These perches are used to maintain territories as described by Henning et al. (1997), who note that adults also feed at flowers and damp patches.

Food plants

The recorded food plants are grasses. Le Pelley (1959) lists Cenchrus purpureus (= Pennisetum purpureum ) in Uganda, Forsyth (1966) gives Paspalum sp. and Zea mays (maize) in Ghana, and Sevastopulo (1975) lists Panicum trichocladum , C. purpureus (= Pennisetum purpureum ) and grasses generally from East Africa (this entry appears against both B. fatuellus and B. lugens , and I assume it applies to both). Sevastopulo (unpublished) does not mention Panicum trichocladum as a food plant, so the origin of this record is not clear. Vuattoux (1999) reared ten specimens in Côte d’Ivoire from several different grasses: five on Setaria barbata , two on Digitaria atrofusca (= D. seminuda ), one on Setaria megaphylla and two on unidentified grasses.

Larsen (1991) lists Ehrharta , Oryza , Zea , Cenchrus (= Pennisetum ) and Panicum , but I have been unable to confirm Oryza from the literature. Ackery et al. (1995) list only Ehrharta , Cenchrus (= Pennisetum ), Panicum and Setaria . Later, Larsen (2005) lists Setaria , Cenchrus (= Pennisetum ), Panicum , Setaria and Digitaria ; he also reports his observation of oviposition on Imperata cylindrica in Nigeria.

In South Africa, Murray (1959), Pringle et al. (1994) and Henning et al. (1997) give Ehrharta erecta and Setaria megaphylla (= sulcata) as food plants, while Dickson & Kroon (1978) also include “other grasses not specifically recorded”.

I have reared B. fatuellus on Megathyrsus maximus (= Panicum maximum ) and another (non-flowering) grass in Kenya, and? Panicum (s.l.) sp. in Côte d’Ivoire. TCEC raised a specimen from an ovum laid on an unidentified grass in a forest glade at Ambangulu in the West Usambaras, Jun 2001.

Leaf shelters

Two 4–5mm n-2 caterpillars collected on an unidentified grass in Côte d’Ivoire (89/205B) made a two-cut shelter just before the leaf tip, by cutting two notches from the edge of the leaf, 25mm apart, and rolling the flap downwards to make a tube. The larger caterpillars shelter in a rolled leaf, and feeding is distal to this ( Henning et al. 1997).

Caterpillar

Clark (in Dickson & Kroon 1978) illustrates two different caterpillars of this species from South Africa. The first resembles one of those illustrated here (Figure 17.2); the second has the dark line in each half of the face narrower, and not extending basally, and the clypeus more extensively white. Henning et al. (1997) include a photograph of a caterpillar from South Africa, similar to that shown here as Figure 17.3–4. Although Clark (in Dickson & Kroon 1978) documents five instars, Sevastopulo (unpublished) recorded six at the Kenya coast.

Up until the end of the penultimate instar, caterpillars have a plain, dark head; that of instar n-2 measured 1.2 x 1.2 mm (91/41). The head of the penultimate instar measures 1.8 x 1.9mm wide x high (n=2); it may be uniformly dark, but in one case (91/41) had diffuse slightly paler areas on the epicranium, in front of the stemmata and on the frons; body green with a white dorsolateral line and a diffuse pale lateral line (87/23). Only in the final instar do the caterpillars develop a variably marked black and white head ( Figure 17 ), 2.5 x 2.9mm wide x high (n=3). A description was prepared of a final instar caterpillar collected at Arabuko-Sokoke Forest on M. maximus (87/23), which measured 18mm when newly moulted and 37mm when mature. Head wider near base; slightly indent at vertex; dark brown; face white, with dark brown sutures, and a black line running from about half way between top of adfrontals and vertex, parallel to epicranium, meeting adfrontal suture a little below apex; basal part of this line then curves laterally and becomes more diffuse; a vertical line in basal half of clypeus (similar to Figure 17.4, but the brown line is narrower in the described specimen); scattered short, pale, erect setae. T1 concolorous with body. Body light yellowish green; dorsal line darker green, becoming translucent as the caterpillar matures; well marked pale dorsolateral and lateral lines, becoming more diffuse, as the caterpillar matures; ventrally, spiracles and all legs whitish. I recorded that the wax glands develop ventrally in the mature final instar caterpillar as a double patch on A8 and a single patch on A9 for one caterpillar (87/23, Arabuko-Sokoke Forest), on A5 and A6 for another (91/41, Kakamega Forest), and on A7–A8 for a third (89/205B, Côte d’Ivoire); further observations are needed to clarify this. The final instar takes about 13 days. Development from eclosion to pupation can take 33 days at the coast (Sevastopulo unpublished).

Pupa

The pupa, typical of the group, is formed partially exposed in a leaf only partly rolled and held with silk basal and distal to the pupa ( Figure 18 ). The shelter is lined with white waxy powder, but this is not on the pupa itself. Male pupa 87/23 was 31mm long and about 5mm at the widest; slender, with a straight frontal spike 2.5mm long; light green; narrow subdorsal lines about 1mm apart. Pupation takes 10–19 days.

Figures

FIGURE 17. Final instar caterpillars of Borbo fatuellus. 1, dorsolateral view; collected as penultimate instar caterpillar on Megathyrsus maximus, Arabuko-Sokoke Forest, 28. ix. 1987; moulted to final instar 2. x.; photographed 12. x., 37 mm; pupated 15. x., ref. 87 / 23; 2, detail of head, anterolateral view; collected as n- 2 caterpillar on unidentified grass, Kakamega Forest, 17. vi. 1991; moulted to final instar 7. vii.; photographed 7. vii., pupated 18. vii.; 91 / 41; 3, final instar, anterodorsolateral view, collected as small caterpillar on unidentified grass (? Panicum (s. l.) sp.), Adiopodoumé, Côte d’Ivoire, 28. v. 2005; moulted to final instar 17. vi.; photographed 17. vi., 22 mm; pupated 30. vi.; ref. 89 / 205 B. 4, final instar, anterolateral view of head; details as 3.

FIGURE 18. Pupa of Borbo fatuellus, dorsal view, collected as small caterpillar on unidentified grass (? Panicum (s. l.) sp.), Adiopodoumé, Côte d’Ivoire, 28. v. 2005; pupated 30. vi.; photographed 30. vi.; adult 19. vii; ref. 89 / 205 B.