Borbo borbonica borbonica Boisduval, 1833

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 : 18-21

Borbo borbonica borbonica Boisduval, 1833 ( Figures 13–16 )

The nominate subspecies is widespread in sub-Saharan Africa, and also found in Madagascar, Mauritius and La Réunion, the type locality ( Boisduval 1833). Subspecies morella Joannis is found on the Seychelles and Aldabra, and ssp. zelleri Lederer in North Africa and parts of the near East ( Evans 1937a, 1949; Larsen 1984). Larsen (1991) notes that there seem to be differences in genitalia between some populations, and so location-specific life history information may useful to interpret this.

In Kenya, it is reported plentiful in the Chyulu Hills by Van Someren (1939) and fairly common in Makardara Forest ( Sevastopulo 1974). I have found it widespread and fairly common from the Kenya coast inland to Nairobi and the edge of the Rift Valley (Muguga, c. 2100m), although it is reported to be migratory and also occurs in western Kenya ( Larsen 1991). On 6 Apr 1991 I found it extremely abundant in the vicinity of Irima Hill, Tsavo East, in the late afternoon—probably due to a recent mass emergence or mass movement. In Tanzania it is common in “woodlands and open habitats up to 2600m ” ( Kielland 1990).

Food plants

Hargreaves (1932) records this species from Zea mays (maize) in Uganda. However, when he subsequently reviewed the pests of maize in Uganda ( Hargreaves 1939), he did not mention B. borbonica , but instead discussed B. gemella , referring to the caterpillar as “very pale green with darker longitudinal lines and blackish or reddish brown marked head”. It seems rather likely that Hargreaves’ (1932) record of B. borbonica was subsequently treated as B. gemella in Hargreaves (1939). The description of the caterpillar of B. gemella is inadequate, but could refer to B. borbonica , or other species, such as Pelopidas mathias . Le Pelley (1959) lists the record from Hargreaves (1932), while Sevastopulo (1975) includes maize, based on Le Pelley (Sevastopulo unpublished), and “grasses generally”. Subsequent authors have repeated this Zea food plant record with no indications of new observations ( Larsen 1991; Ackery et al. 1995; Henning et al. 1997; Larsen 2005). Accordingly, although maize is a likely food plant, the records of it being used should be considered unconfirmed.

Frappa (1937) found B. borbonica abundant on upland rice in Madagascar, while Bouriquet (1949) reports that it caused minor damage in that country. Brenière (1976) reports B. borbonica as a pest of rice in West Africa, noting that damage is minimal and outbreaks terminated by the action of natural enemies. In the NHM Dry Early Stages Collection there is material reared by P.P. Graves on rice in Egypt; the preserved caterpillar and three pupae match those described here.

From southern Africa, Dickson & Kroon (1978) and Pringle et al. (1994) give various grasses including Ehrharta spp., and this is repeated in Kielland (1990). Larsen (1991) gives the food plants as “many Poaceae ” and lists Ehrharta , Oryza , and Zea based on the above records, and Cenchrus (= Pennisetum ), which seems to be the first record of this genus. Ackery et al. (1995) and Henning et al. (1997) repeat these records, but Heath et al. (2002) list only “species of grass”.

Williams (1989) lists sugar cane, rice and various wild grasses as food plants in Mauritius; while for the same island Davis & Barnes (1993) note a preference for Panicum (s.l.) spp. Guillermet (2011) lists rice and Cenchrus purpureus (= Pennisetum purpureum ) from La Réunion.

Hence, Larsen (2005) adds Leersia and Sorghum to those previously recorded; Leersia is based on my observation below, but I have not traced another record from Sorghum .

I have reared this species just once—from a caterpillar on the fine leaved grass Leersia hexandra (91/21) in a patch of stream-side swamp at the bottom of my garden in Kyuna, Nairobi (the same food plant is also used by Metisella midas and Gegenes niso at this site). In captivity it also fed readily on Megathyrsus maximus .

Ovum

Ova extracted from a captured female were dome-shaped with a very narrow flange around the base and measured 1.1 x 0.6mm wide x high. Two uneclosed ova associated with the caterpillar that I found (91/21) measured 1.1–1.2 x 0.5–0.6mm and are considered to belong to this species. The eclosed ovum associated with 91/21 was laid singly on a grass leaf and the shell eaten by the caterpillar except for base. Sevastopulo (unpublished) reared this species from ova in Kampala, Uganda. He describes the ovum as “very pale blue-green, bun-shaped, under a powerful hand lens minutely punctuate”. Sevastopulo’s ova hatched after 6 days.

Leaf shelters

By rolling a grass leaf.

Caterpillar

Sevastopulo (unpublished) records five instars. Instar 1: head black; body whitish green; narrow black dorsal plate on T1. Instar 2: similar but plate on T1 not visible; the head capsule of instar n-3 of 91/21 measured 0.7 x 0.7mm and had scattered, very short, pale setae. Instar 3: similar, but head very dark brown with a[n inverted] V-shaped mark from vertex to outside mandibles; body with darker green dorsal line and pale subdorsal and dorsolateral lines; the head capsule of instar n-2 of 91/21 measured 1.1 x 1.1 mm and had setae as previous instar.

The penultimate instar is shown in Figure 14 ; the head capsule measures 1.5 x 1.6mm wide x high. Sevastopulo (unpublished) described it: “head greenish, the clypeus outlined by a fine red-brown line and with a red-brown stripe along the median suture, a red-brown stripe, edged internally with a white, forming a rough triangle from vertex to outside the mandibles.” The cast head capsule of 91/21 is light brown, with translucent areas which are green in life, and no white border to the lateral stripe; scattered, very short, pale setae. Instar 4 lasted 5 days at Kampala (Sevastopulo unpublished) and 8 days at Nairobi.

The fifth instar ( Figure 15 ) grows to 31 mm or more; body green with the dorsal line darker; pale, laterally diffuse subdorsal line; narrow, pale, subdorsal line; two weak, pale, diffuse, lateral lines; spiracles, pale brown, inconspicuous; legs concolorous; anal plate slightly elongate with a fringe of stout outwardly projecting pale setae; the body has sparse, short, pale, simple setae, not evident to the eye but just visible in Figure 15.2. In Figure 15.2, it can be seen also that the head, which measured 2.4 x 2.8mm wide x high, has a red-brown line from the apex to stemmata, slightly darker posteriorly and with a white border anteriorly. As for the penultimate instar, the cast head capsule is translucent with a brown lateral line, but no sign of the pale border; scattered very short, pale setae not visible in Figure 15.2. Sevastopulo (unpublished) describes the lateral line as crimson, and notes that it is not always present, although the white line is. The mature caterpillar develops wax glands ventrolaterally: two small ones on A7 and a larger one on A8. The fifth instar took 12 days at Nairobi, and a caterpillar reared by Sevastopulo (unpublished) at Kampala took 28 days from eclosion to pupation.

Pupa

The pupal shelter, made from a grass leaf, is lined with white waxy powder, and the pupa is typical of the grass feeding members of this group ( Figure 16 ). Pupation took 11 days at Kampala (Sevastopulo unpublished) and Nairobi.

Figures

FIGURE 13. Adult male of Borbo borbonica at rest, Diani Beach, 15. xii. 1989.

FIGURE 14. Penultimate instar caterpillar of Borbo borbonica, collected 24. iii. 1990 as n- 2 caterpillar on Leersia hexandra, Kyuna Estate, Nairobi; moulted to penultimate instar 28. iii.; photographed 28. iii., 9 mm; moulted to final instar 5. iv.; ref. 91 / 21.

FIGURE 15. Final instar caterpillar of Borbo borbonica, collected 24. iii. 1990 as n- 2 caterpillar on Leersia hexandra, Kyuna Estate, Nairobi; moulted to final instar 5. iv.; pupated 17. iv.; ref. 91 / 21. 1, dorsolateral view, photographed 10. iv., 32 mm; 2, detail of head, anterolateral view; photographed 7. iv.

FIGURE 16. Pupa of Borbo borbonica, dorsolateral view; collected 24. iii. 1990 as n- 2 caterpillar on Leersia hexandra, Kyuna Estate, Nairobi; pupated 17. iv.; photographed 21. iv., 26 mm; adult female 28. iv.; ref. 91 / 21.