Pelopidas thrax Hubner 1821

Pelopidas thrax Hübner, 1821 (in Hübner [1819 –1826]) (Figure 12)

Pelopidas thrax is widespread throughout sub-Saharan Africa, Cyprus, Egypt and the Middle East to Pakistan and North-west India (Evans 1937a, 1949; Larsen 2002, 2005). Until recently, it was treated as two separate subspecies: the nominate thrax, described from Syria, and found in Cyprus and from Egypt to North-west India (Evans 1937a, 1949; Larsen 2002); and subspecies inconspicua (Bertolini), described from Mozambique and found throughout sub-Saharan Africa (Evans 1949; Dickson and Kroon 1978; Larsen 2005). However, Larsen (2005) examined adult material from throughout this range and concluded that Evans (1937a, 1949) incorrectly treated thrax as an extreme dry season form, exemplified by specimens from Iraq and that P. th r a x is a single subspecies throughout its range. Accordingly, he synonymised inconspicua under thrax. I don't consider this a common species in Kenya, perhaps because it may be associated more with grassy places than savannah or forest.

Food plants

The reported food plants of P. t h r a x are all grasses, but almost all published records seem to be secondary sources, and I have failed to track down many original food plant records. For example, it has been reported several times as a pest of rice (e.g. Larsen 1991, 2005), yet Heinrichs & Barrion (2004) do not mention this species in their comprehensive review of rice pests in West Africa, although they do include P. mathias (see above). Pelopidas thrax has been referred to as the lesser millet skipper, but this may simply reflect that it is congeneric with P. mathias, which does feed on millet and has been referred to as the millet skipper. Larsen’s (1984) illustration of a caterpillar on a millet leaf is actually P. mathias (see above), and I have found no substantive records from this host.

In South Africa, Murray (1959) lists Ehrharta erecta and other grasses as the food plants. Dickson & Kroon (1978) record the food plant as Imperata cylindrica (= I. arundinacea); noting that it has also been reared on Ehrharta erecta and other suitable grasses, and Pringle et al. (1994) repeat these grasses. Van Someren (1974) gives grasses, as does Sevastopulo (1981), but it is not clear whether this is based on local experience, or generalised from earlier sources.

In Oman I have found caterpillars on a large, coarse grass, Saccharum kajkaiense and/or S. ravennae (see Feulner & Karki 2010) growing in the wadis of the Hajar Mountains (Cock 2010a), but I have not reared it from sub-Saharan Africa.

Ovum

Yellow and hemispherical according to Dickson & Kroon (1978) changing to salmon colour.

Leaf shelters

A typical grass tube according to Dickson & Kroon (1978). In Oman, I noted that small caterpillars make a shelter from a single leaf, by rolling the edges upwards until they meet, and holding the edges together with strands of silk. They then feed from the edge of the leaf lamina distally or basally to the shelter, or both. Larger caterpillars draw together several leaves and hold the edges together with silk strands to form a tube (Cock 2010a).

Caterpillar

Clark (in Dickson & Kroon 1978, Plate 32) provides excellent paintings of the life history on “grass”. The final instar caterpillar is pale yellow-brown, with a darker dorsal line and a brown lateral line. The head is pale brown, the posterior margin and lateral areas dark, as are the epicranial and clypeal sutures. The earlier instars are similar, but the head is dark.

Makris (2003) illustrates a caterpillar of P. t h r a x from Cyprus, which is very similar to that illustrated by Clark (in Dickson & Kroon 1978). The head is shown almost in lateral view, but with a slight anterior perspective. It is light brown with a very strong lateral stripe, which extends at least partly to the posterior margin; the epicranial suture and some or all of the adfrontals and clypeus are black, and there is a trace of a black streak extending dorsally on the epicranium from the adfrontals.

The caterpillars which I found in Oman (Cock 2010a) had rather different caterpillars, and six instars, the last of which was larger than the South African material, with the head predominantly light brown, with variable darker stripes (Figure 12). Wax glands are formed ventrolaterally on the anterior margin of abdominal segments 7 and 8 when caterpillars are mature. Whereas the head capsules of all the early instars illustrated by Clark (in Dickson & Kroon 1978) are black, those of the Oman material are variably pale brown with more or less pronounced black markings.

Pupa

In Oman, the pupa on Saccharum sp. (Figure 12.4) is formed in the shelter of the mature caterpillar, which is lined with silk. The inside of the shelter is covered with a thin deposit of white waxy powder, which is not found on the pupa itself (Cock 2010a). The pupa illustrated by Clark (in Dickson & Kroon 1978, Plate 32) is slender, pale yellow-brown, with a slightly downturned, dark, frontal spike, and the proboscis sheath projecting about one segment beyond the wing cases. The pupa from Oman differs from this in that the frontal spike is concolorous with the rest of the pupa and slightly upturned.

Natural enemies

One fifth instar caterpillar collected in Oman was parasitised by a gregarious eulophid parasitoid, and another produced a tachinid larva when in the sixth instar (Cock 2010a); neither has been identified.