Spialia ploetzi Aurivillius 1891
Creators: name: Cock, Matthew J. W.
Publisher: name: Zenodo
Year: 2016
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Lepidoptera
Hesperiidae
Spialia
Spialia ploetzi

description: Spialia ploetzi Aurivillius, 1891
The similarities described here between the life histories of S. dromus and S. ploetzi confirms De Jong's placement of S. ploetzi in the dromus group of Spialia (De Jong 1978). The type locality of S. p. ploetzi is Cameroon (Aurivillius 1891), and its range extends to western Kenya. De Jong (1977) divided S. ploetzi into two subspecies: S. ploetzi occidentalis De Jong (Figure 23.1) from western Africa (type locality Ghana) and the nominate subspecies (Figure 23.2) from eastern Africa; the dividing line between the two subspecies runs through Cameroon.
I have only encountered this species twice in Kenya: both times in Kakamega Forest, where the D267 crosses Ikuywa Stream. This species is restricted to the western forests and is scarce there.
Adult behaviour. I once found two males drinking at mud in Kakamega Forest (Jan 1989).
Food plants. Fontaine (1988) reared this species (as S. rebeli Higgins, a synonym) on an unidentified food plant at Isiro, north-eastern DR Congo in 1960. Larsen (1981, 1991, 2005) describes a single sphecid wasp visually hunting for shelters of caterpillars of S. ploetzi on a Triumfetta sp. in a Lagos hotel garden, Nigeria. From his account, he does not seem to have reared voucher specimens, and given the habitat, it seems more likely that the caterpillars he observed were S. dromus, but I have not been able to discuss this possibility with him. Nevertheless, his observations that the individual wasp was hunting visually for bits of leaf under surface visible from above, that wasps bit through the leaf to reach the caterpillar inside (rather than lifting the flap), and that caterpillars that had folded their shelters under the leaf were not found, offer useful general insight to the roles of leaf shelters and predators.
I have not encountered caterpillars of this subspecies in Kenya, but have reared ssp. occidentalis from caterpillars collected on a Triumfetta sp. in Côte d'Ivoire (Figure 23.1) and ssp. ploetzi on the same food plant in Cameroon (Figure 23.2). Larsen (1991) reports my record of rearing ssp. occidentalis from Triumfetta sp. in Côte d’Ivoire and his from the same food plant in Lagos, Nigeria (although this may be an assumption on his part—see previous paragraph). Vuattoux (1999) found this subspecies on T. rhomboidea in Côte d’Ivoire. I noted no significant difference between the caterpillars of the two subspecies, although the pupae differ in my small samples
Leaf shelters. A leaf shelter of a young caterpillar of S. p. ploetzi in Cameroon (MJWC 90 /204) was formed from a leaf lobe at the end of a major vein (Figure 24.1). A small flap was folded up each side of the vein to form the shelter, and feeding was in small patches (c. 1.5mm diameter), four in the small area of leaf distal to the shelter, and 21 from the leaf basal to the shelter, arranged mostly along the main vein.
Of the two mature leaf shelters of S. ploetzi occidentalis which I collected in Côte d'Ivoire (MJWC 88 /205), one was a flap 25 x 13 mm folded upwards from the edge of the leaf, and the second was a large section of leaf 50 x 19 mm folded upwards. A pupal shelter was distinctive, being formed from two small leaves about 35mm long, one on top of the other; both leaves were evenly pierced by 1mm holes over the entire surface except the margins where they were joined.
Caterpillar. The caterpillar (Figure 24.2–3) is superficially similar to that of S. dromus, although the details of the setae on the head differ. In view of this similarity, all caterpillars apparently of S. dromus on Triumfetta spp. in Kakamega Forest should be carefully examined under magnification or reared as they may prove to be S. ploetzi.
The final instar of ssp. occidentalis (MJWC 88/205 A) was 22mm long (Figure 24.2). Head 2.2 x 2.6mm wide x high; rounded, slightly indent at vertex; black, shiny, reticulate on epicranium, rugose on adfrontals and frons; each adfrontals with two round brown plaques in dorsal portion (the dorsal plaque was missing on one side); no setae on each side of epicranial suture, adfrontals, frons; on epicranium part of face a few very short or short pale, erect, narrow, linear setae; ventrally on face longer, erect, pale, simple setae; dorsally and laterally short to long black, twisted linear setae up to 0.6mm long and 0.14mm wide; posterior margin with pale setae similar to face. T1 with groove separating posterior third; marked in black and yellow (pale whitish on exuvia): rounded spot on anterior two-thirds of dorsum; quadrate spot on anterior two-thirds dorsolaterally; oval brown plaque subdorsally near anterior margin (lateral part of pronotum not visible in exuvia, but expected to have a similar plaque); with scattered short and long white, erect, narrow linear setae, slightly dilated and truncate at apex; legs black. Body greenish white; covered with short and long erect, pale, blunt setae on white bases; legs concolorous; spiracles inconspicuous.
The final instar of ssp. ploetzi (MJWC 90/204) was similar; head 2.4 x 2.5mm wide x high; the very short, pale, simple setae extend to the frons and adfrontals but are almost absent from the centre of the face; two round brown plaques on upper part of each adfrontal; otherwise as ssp. occidentalis. The difference in very short setae on the head may be due to abrasion rather than of significance. The head of the penultimate instar of ssp. ploetzi was similar to that of the final instar; 1.7 x 1.7mm wide x high; setae similar but less conspicuous, the black twisted linear setae up to 0.4mm long and 0.08mm wide.
Pupa. The pupa of ssp. occidentalis was 13mm long; no wax bloom; the cuticle transparent apart from faint brown bars subdorsally on the posterior margin of A4–A5, and brown markings on front of head and a vertical bar in the anterior and posterior halves of each eye; initially white (Figure 25), the pupa turned dark as it developed; short pale and light brown erect, simple setae; spiracles dark brown, conspicuous; spiracle T1 similar to other member of the genus with the posterior margin raised on a vertical wall, 0.52 x 0.70 x 0.36mm wide x high x deep; small brown oval plaques subdorsally on anterior margin A2–A5; similar plaques ventral to spiracles on A4–A8. The pupal stage lasted 18 days.
In contrast, the pupa of ssp. ploetzi was extensively dark brown, apart from the wings, appendages and the abdomen laterally adjacent to the dorsum of the wings, and abdomen intersegmental regions; white, erect, simple setae; oval brown plaques as ssp. occidentalis; spiracles dark; spiracle T1 0.30 x 0.60 x 0.28mm wide x high x deep.
Discussion. Larsen (unpublished) planned to raise occidentalis to species level, based on differences in the male genitalia, the patterns of the hind wing, and the absence of intergrading in the area between the extreme east of Nigeria and the Sanaga River, even when the two forms occurred in close proximity at different altitudes as little as 1km apart.
My limited observations indicate that the caterpillars of ploetzi and occidentalis are very similar, but I found differences in the colouring of the pupae. However, without more material of both to assess individual variation in pupal colour, I conclude that it would be premature to suggest these cuticle colour differences are significant, given the amount of variation in pupal colour noted in some other species here. Certainly my observations are not incompatible with Larsen’s view, but with such limited biology observations to support this, I make no change to the current taxonomy.
description: Published as part of Cock, Matthew J. W., 2016, Observations on the biology of Afrotropical Hesperiidae (Lepidoptera) with particular reference to Kenya. Part 10. Pyrginae, Carcharodini, pp. 301-350 in Zootaxa 4173 (4) on pages 329-332, DOI: 10.11646/zootaxa.4173.4.1, http://zenodo.org/record/256597