Xanthodisca vibius Hewitson 1878

Xanthodisca vibius Hewitson, 1878

This species is found from Cameroon to Kenya and south to Malawi (type locality Gabon) (Ackery et al. 1995, Larsen 2005). In Kenya, it is a scarce species restricted to Kakamega Forest, and perhaps other western forests. MJWC never saw the adult, but did once rear it from a caterpillar.

Food plants. Le Pelley (1959) gives Amomum sp. as the food plant in Uganda, a record apparently repeated by Sevastopulo (1975), Kielland (1990) and Ackery et al. (1995). MJWC reared this species from Aframomum zambesiacum zambesiacum, the normal food plant of Semalea pulvina in Kakamega Forest. TCEC has reared this species from the Rondo Plateau, south-east Tanzania and at Kihansi, south central Tanzania, from Aframomum sp. The former may be the origin of the record of Aframomum in Heath et al. (2002). It seems likely that the early record from Amomum should be referred to Aframomum.

Caterpillar. MJWC reared this species once from the final instar from amongst a batch of S. pulvina caterpillars collected from Kakamega Forest 1 July 1990 (MJWC 90/70G). He did not notice any differences in the shelters or caterpillars at the time, and was surprised when one pupa produced a female X. vibius. Examination of the cast head capsule revealed no qualitative difference between these two species; the clypeus, frons, adfrontals and a stripe down the epicranial suture light brown; the rest of the epicranium rugose, the raised areas darker brown and the pits lighter brown; posterior margin basally pale; it measured 2.2 x 2.75mm wide x high, almost exactly the same as that of the final instar of S. pulvina (2.2 x 2.7mm).

TCEC has reared this species at Kihansi and the Rondo Plateau, Tanzania, from Aframomum sp. It can be seen that the caterpillar (Figure 22) does indeed resemble those of S. pulvina, but was noted to be more squat, green, and with a squared off anal plate with a dark transverse mark.

Pupa. The 18mm pupa that MJWC reared is very similar to that of S. pulvina, but the most obvious difference is in the dimensions of the semi-circular body around the T1 spiracle: the central hole measured 0.67mm across ventrally-dorsally, and the rim measured 0.5mm across dorsally, 0.5mm posteriorly and 0.28mm ventrally. In addition (based on the emerged pupae of both) the pupa of X. vibius is more uniformly pale compared to that of S. pulvina; an irregular dark mark subdorsally between the T1 spiracles, another dorsolaterally on the anterior margin of T3, A1 and A4-A6; proboscis reaches to the end of the penultimate abdominal segment. The pupa took 19 days until the adult emerged. The pupa documented by TCEC from Kihansi (Figure 23) is similar, but is darker and the distribution of dark markings differs, suggesting there is probably significant individual variation in colouring.