Gegenes niso brevicornis Plötz, 1884

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 : 31-34

Gegenes niso brevicornis Plötz, 1884 ( Figures 25–29 )

In the older literature, including Evans (1937a), this species was treated as G. letterstedti Latreille , but Evans (1947) established the identity of G. n i s o, making letterstedti a synonym. The nominate ssp. niso was described from the Cape of Good Hope ( Linnaeus 1764) and is restricted to southern Africa, while ssp. brevicornis (Plötz) is widespread and common over the rest of sub-Saharan Africa ( Evans 1937a, 1947; Ackery et al. 1995). Evans (1937a) separates the two subspecies only on the basis of size. The early stages of the two subspecies do not seem to differ, and the division into subspecies may merit reconsideration.

This is perhaps the commonest and most widespread of upland Kenyan skippers. For example, Van Someren (1939) records it as by far the commonest skipper throughout the Chyulu Hills from 3,000–6,500 ft. (910–1830 m).

Adult behaviour

I have observed a male feeding at a bird dropping (Kakamega Forest, 16.vi.1991), holding its fore wings closed, and its hind wings partially open.

Life history

The life history of ssp. niso has been described and illustrated in detail by Clark (1940) and Henning et al. (1997) illustrate the caterpillar and pupa. My less detailed observations of ssp. brevicornis below are very similar.

Food plants

Subspecies niso in South Africa feeds on Themeda triandra (recorded for the synonym ocra), Ehrharta erecta , Cenchrus clandestinus (= Pennisetum clandestinum ), and other soft grasses ( Dickson & Kroon 1978, Pringle et al. 1994). The last two are listed as food plants of G. niso brevicornis by Larsen (1991, 2005) and Heath et al. (2002) although they do not seem to have been reported separately for this subspecies.

For subspecies brevicornis, Descamps (1956) records this as a pest of rice in Cameroun and provides a description of the caterpillar and pupa. Van Someren (1974) gives the food plants as grasses. While Sevastopulo (1975) includes this species in his list, there is no food plant recorded against it; probably the record of “grasses generally” against the preceding G. hottentota was also intended to refer to G. n i s o. Larsen (2005) adds Zea , Imperata and Hyparrhenia as food plants; the first based on my rearing, but I have not traced the origin of the other two records.

S.C. Collins has reared a female from Setaria sp. July 2007 at Karen, Nairobi (in ABRI). I have reared caterpillars from Leersia hexandra and from a young plant of Zea mays (maize) at the six leaf stage, and observed oviposition on another species of short grass. Both produced adult males so there is no doubt about the species reared. In captivity, caterpillars will feed on Megathyrsus maximus (= Panicum maximum ), and in the wild will almost certainly use a variety of grasses.

In Oct 1989, I confined a female captured in Ngong Forest, Nairobi (89/81), in a 58mm diameter plastic pot with several grass leaves, and by the next day it had laid seven eggs on the wall of the container. I kept her for a further day in rectangular box (137 x 78 x 60 mm) with a mixture of cut grass leaves and a pad of tissue wet with water and honey and a further 19 ova were laid. The ova hatched after 10 days and the neonate caterpillars were offered a mixture of five grasses used by Hesperiinae as food including Cynodon nlemfuensis , Imperata cylindrica (?), Megathyrsus maximus and Zea mays . The caterpillars never really settled down to feeding, only three reached the second instar, and none reached the third instar.

Ovum

Ova are smooth, off-white and almost hemi-spherical ( Figure 26 ). Sevastopulo (unpublished) describes the ovum as bun shaped. Dickson & Kroon (1978, Plate 38) note that the ovum of ssp. niso develops salmon maculae as it matures.

Leaf shelters

A third instar caterpillar on maize (88/110) cut a broad notch from one lamina edge to the mid-rib, and folded the distal 25mm upwards to make a shelter; subsequent feeding was immediately basal to the shelter, and in a broad notch from the opposite leaf margin ( Figure 27 ). Fifth instar caterpillars probably do not make a significant shelter unless feeding on a broad-leaved grass.

Caterpillar

The body of all instars is striped green, but in the fifth instar the definition of the dorsal stripe by the broad white sub-dorsal stripes becomes especially marked ( Figure 28 ). The head capsule of the first and second instar caterpillars is black, but in the third instar it is translucent light brown, with a dark brown stripe laterally down the outside of the head, and a short vertical stripe on the middle of each epicranium in the lower half of the face; body whitish green; dorsal line clear, darker green; narrower white subdorsal, dorsolateral and ventrolateral lines (88/ 110). The fourth instar caterpillar has a green head with a pink-brown stripe down each side, bordered with light white-green.

The fifth instar caterpillar (88/110, 90/6G) has a green head with a pink to red to light brown stripe from vertex laterally to stemmata, which may be bordered with yellow anteriorly and posteriorly ( Figure 28 ), 2.0 x 2.5 mm wide x high. Dorsal line on body 0.5–0.75mm wide, dark green with a narrow, pale central line; bordered by a broad 0.5 mm white subdorsal line; laterally greenish white above a narrow white lateral line; below this two greenish lines with diffuse pale line through spiracles; stronger white ventrolateral line; spiracles pale, inconspicuous; legs concolorous with body. The wax glands develop as subventral rectangles on A7 and A8 (88/ 110). The last three instars take 6, 6–8 and 9–13 days respectively.

Pupa

According to Clark (1940) pupation of ssp. niso takes place at some distance from the food plant, for example on a leaf of a tree. In captivity, my specimens pupated in a leaf shelter similar to those used by Borbo spp. The pupa is 21–24mm long, with a 2mm frontal spike; bright green with narrow white subdorsal and dorsolateral lines; and two fainter pale ventrolateral lines. It is held in its shelter by a single strand of silk over the thorax ( Figure 29 ), and the shelter is lined with white waxy powder. Pupation takes 13–16 days, under Nairobi conditions, but one reared by Sevastopulo (unpublished) at Kampala took just eight days.

Figures

FIGURE 25. Adult Gegenes niso brevicornis. 1, a worn male nectaring, Ashnil Mare Camp, Masai Mara, 16. viii. 2010 (A. D. Warren); 2, female at rest, Kakamega Forest, 15. vi. 1991 (vouchered).

FIGURE 26. Ova of Gegenes niso brevicornis laid in captivity on artificial substrate, 17. x. 1989; photographed 18. x.; eclosed 25. x.; ref. 89 / 81.

FIGURE 27. Diagram of leaf shelter of Gegenes niso brevicornis on leaf of young maize plant, collected Kyuna Estate, Nairobi, 5 Nov 1988, approximately 2 x life size; ref. 88 / 110.

FIGURE 28. Final instar caterpillars of Gegenes niso brevicornis. 1, newly moulted, dorsal view, collected as n- 2 instar caterpillar on maize, Kyuna Estate, Nairobi; moulted to final instar 17. xi.; photographed 17. xi., 22 mm; pupated 26. xi.; ref. 88 / 110; 2, detail of head, anterior view; as (1); 3, detail of head, anterolateral view, collected as n- 3 instar caterpillar on Leersia hexandra, Kyuna Estate, Nairobi, 30. i. 1990; moulted to final instar 6 – 9. ii.; photographed 10. ii., 22 mm; pupated 20. ii.; ref. 90 / 6 G.

FIGURE 29. Pupa of Gegenes niso brevicornis, collected as n- 3 instar caterpillar on Leersia hexandra, Kyuna Estate, Nairobi, 30. i. 1990; pupated 20. ii.; photographed 22. ii., 21 mm; male emerged 5. iii.; ref. 90 / 6 G.