Acleros mackenii instabilis Mabille, 1890

Cock, Matthew J. W. & Congdon, Colin E., 2013, Observations on the Biology of Afrotropical Hesperiidae (Lepidoptera). Part 5. Hesperiinae incertae sedis: Dicotyledon Feeders, Zootaxa 3724 (1), pp. 1-85 : 26-30

Acleros mackenii instabilis Mabille, 1890

Evans (1937) recognised six different forms of Acleros mackenii Trimen, 1868 (type locality Durban, South Africa) from throughout sub-Saharan Africa, some geographic and some seasonal. The dry season form from East Africa he referred to f. olaus Plötz, 1884 (type locality Loanga, [ Burkina Faso]) which has upper surface markings in both sexes and the hind wing under surface with pale markings, and the wet season form as f. instabilis (type locality Zanzibar) with the male upper surface unmarked, and the hind wing under surface dark. Ackery et al. (1995) suggest that olaus may be a distinct West African species. Larsen (2005) summarises the unpublished views of L.A. Berger that there are three species involved, which Larsen treats as subspecies: olaus from West Africa, instabilis from central to East Africa and the nominate mackenii from southern Africa. Pending further study, we follow this treatment here. However, we are not convinced that dry season and wet season forms explains the variation seen in Kenya, and further careful collecting, rearing and study are needed to clarify the causes of variation.

It is widespread in forested situations more or less throughout Kenya, including the Chyulu Hills where it can be very common ‘frequenting the undergrowth of Acanthaceae’ ( Van Someren 1939) and Shimba Hills where it is uncommon ( Sevastopulo 1974). Generally, this is one of the common forest species everywhere in Kenya.

Adult behaviour

The males ( Figure 29.1 ) defend territories. Walking along the tracks of Ngong Forest, Nairobi, often every sunlit patch beside the track will have one or two males perched on vegetation at 1–2.5 m above the ground. These males will rise to attack other butterflies, and indulge in fast swirling combat with other males, before returning to one of a few select perch sites. In flight often only the white tip of the abdomen can be seen.

MJWC has also noted that on hot days, both sexes (but perhaps the female more than the male) will perch on low vegetation (<0.3 m) or the ground in shady portions of the forest ( Figure 29.2 ). Both sexes come readily to flowers such as Justicia flava . Gifford (1965) states that it is ‘gregarious at night’.

Food plants

In Kenya, MJWC’s experience suggests the normal food plants are Fabaceae vines ( Larsen 1991), particularly species of Vigna . In the Shimba Hills (by the bridge on the Marere Waterworks track), the food plant was a Vigna sp. with tripetiolate leaves, which sprawled over low vegetation on sandy soil (90/50); at Kisii it was a similar vine with yellow flowers. In Ngong Forest, in spite of repeated searches, MJWC found only one egg ( Figure 30 ) and a shelter (similar to those described below), which were on V. schimperi (MJWC 101), a species with purple flowers. At Thika, MJWC found caterpillars on a similar, non-flowering vine (98/203). Murray (1959) also reported the food plant as “a small leguminous climber” in South Africa.

In contrast to MJWC’s experience, Van Someren (1974) lists ‘ Rhus coriacius ’ (Anacardiacae) and ‘ Acridocarpus longifolius (?)’ (Malphigiaceae), which are repeated by Sevastopulo (1975) as genera only. ‘ Rhus coriacius ’ is not a published name, but has been applied to R. coriaria , a southern European tree, whose dried fruits are used as a spice in the Middle East. There are six species of Rhus in Kenya ( Beentje 1994), but no obvious equivalent. Van Someren included the annotation ‘(?)’ after Acridocarpus longifolius , so was uncertain of the record or species name. Acridocarpus longifolius is a West African species, and the nearest equivalent in Kenya would be A. zanzibaricus , which is restricted to the coast ( Beentje 1994). These records are repeated by subsequent authors: Kielland (1990), Ackery et al. (1995); Henning et al. (1997 as R. coriarius and A. smeathmanii , the later a synonym of A. longifolius in Tropicos 2012), Larsen (2005), Woodhall (2005). Willis & Woodhall (2010) state that caterpillars ‘feed on species of Searsia (formerly Rhus )’, but this may simply reflect recent taxonomic changes in the southern Africa flora, rather than local knowledge of the food plants. Clark (in Dickson & Kroon 1978) illustrates the life history in detail, but the text of Dickson & Kroon (1978) does not mention the food plants; the illustrations include part of a food plant leaf, but this is not distinctive enough to suggest an identity. Larsen (1991) includes Rhus and Acridocarpus with an element of doubt. Heath et al. (2002) list the food plants as Combretum molle , Terminalia , Quisqualis , Bridelia micrantha , Acridocarpus longifolius , but do not include Rhus ; the first four do not seem to have been mentioned elsewhere, and given the overlap with the food plants of Parosmodes morantii (above), could represent a transcription error.

Given that neither Rhus nor Acridocarpus appear to have been directly confirmed by subsequent workers, it could be that Van Someren’s (1974) records are in error. However, given the possibility that there are more than one species grouped together under the name A. mackenii , it is possible that they use different food plants.

Ovum

The ovum MJWC located in Ngong Forest is (by elimination, comparison to that of Andronymus caesar ( Figure 42 ), and comparison with Clark’s (in Dickson & Kroon 1978) illustration) almost certainly that of Acleros mackenii ( Figure 30 ), but it failed to hatch. This and another ovum were found in the middle of the leaf under surface. The egg was 0.95 x 0.55mm wide at base x high; hemispherical; 19 ribs rising to about 2/3 height, above which additional finer ribs run closer to reticulated apex.

Leaf shelters

Shelters used by the n-2 and penultimate instar caterpillars are made by folding a flap under from the edge of the leaf without making any cuts. Feeding is distal to the shelter. The leaf shelters are formed on leaves well within the canopy, and are far from easy to find; it is necessary to trace likely looking shoots of the vine back through the vegetation through which it has grown. The final pupal shelter is prepared by the fifth instar caterpillar from a single leaf of the host plant. Firstly, the leaf is securely attached to the plant (or the rearing container) with silk to strengthen the petiole; then the caterpillar cuts through the mid-rib just short of the apex, and cuts an irregular arc from the apex to rejoin the mid-rib towards the base of the leaf ( Figure 31 ); the shelter then hangs from the bared mid-rib, and the pupa which is formed with the head to the distal end of the shelter is exposed between the two irregular flaps on each side.

Caterpillar

The penultimate instar caterpillar is dull green with a black head ( Figure 32 ). Head 1.36 x 1.44mm wide x high (n=3), widest near base; sides relatively straight, slightly indent at vertex; T1 concolorous; body dull green with extensive subdorsal and dorsolateral area whitish with translucent dull green speckles; there are just apparent traces of dorsolateral diagonal lines which will be much more developed in the final instar; pale tracheal lateral line; spiracles pale, inconspicuous, except that of A8 more conspicuous; all legs concolorous.

It is only in the final instar that the striking markings of the head become apparent ( Figure 33.2 ). The following description was made from caterpillar 90/50B when 18mm long ( Figure 33 ). Head relatively small, 2.12 x 2.17mm wide x high (n=2,3); rounded, widest in basal half, indent at vertex; epicranium face white, with narrow dark redbrown border along sutures and laterally; within this white area, a horizontal red-brown line at about one third from bottom (this line is dull green in a caterpillar collected at Thika 98/203); the upper part of the white area divided by an angled dull green line from near adfrontal, but stopping short of the dark red-brown border; adfrontals, clypeus and frons dull green; a diffuse dark spot on inner margin of adfrontal just below horizontal line; posterior part of head dull green with irregular white subdorsal, lateral and ventrolateral blotches; posterior margin darker. T1 dull green, dorsal plate concolorous. Body marked with a ‘herring bone’ effect due to dull green ground colour overlaid with whitish yellow, which in turn is speckled with the ground colour especially laterally, and gaps in the yellowwhite overlay make narrow lines of ground colour: a dorsal line; a series of diagonal lines running from the dorsal line to the level of the spiracles; the first running from the anterior margin of A1 to the posterior margin of A2, and the seventh from mid A7 to mid A8; the anterior six of these lines expand dorsolaterally to form a spot from which two small lines radiate, one posteriorly and one posterodorsally; spiracles pale, inconspicuous; all legs concolorous; anal plate pointed posteriorly, almost triangular, with strong white setae. Wax glands develop as a contiguous patch on the underside of A7–8, apart from a narrow ventral line as the caterpillar prepares for pupation. The fifth instar lasts 13–14 days.

Pupa

The pupa ( Figure 34 ) is cryptically coloured, which reflects the fact that it is substantially visible in the camouflaged shelter. No written description was prepared. There is a coating of wax particles inside the pupal shelter, but not on the pupa. The pupal stage lasted 14–16 days.

Natural enemies

MJWC collected a mummified penultimate instar caterpillar on Desmodium repandum in Kakamega Forest , 6 Jan 1989 (89/5) which in view of the associated feeding and shelter constructed was most probably this species or the next. An adult ichneumonid emerged 9 days later .

Figures

FIGURE 29. Adults of Acleros mackenii instabilis. 1, male sunbathing, Ngong Forest, Nairobi, 20 Nov 1988; 2, female showing underside, Kyuna Estate, Nairobi, 12 Nov 1989.

FIGURE 30. Ovum of Acleros mackenii instabilis, collected 11 Nov 1990 on Vigna schimperi, photographed 13 Nov 1990; did not eclose; 90/103.

FIGURE 31. Nearly complete pupal shelter of Acleros mackenii on Vigna sp., collected as caterpillars on Vigna sp. 15 Apr 1990, Shimba Hills, Kenya; diagrams prepared 3 May; pupated 4 May; Approximately 3.2 x life size. A, 90/50A, B, 90/50B.

FIGURE 32. Fourth instar caterpillar of Acleros mackenii instabilis collected on Vigna sp., Shimba Hills, Kenya, 15 Apr 1990; photographed 17 Apr, 12mm; moulted to final instar 23 Apr; 90/50A.

FIGURE 33. Final instar caterpillar of Acleros mackenii instabilis, collected as penultimate instar on Vigna sp., Shimba Hills, Kenya, 15 Apr 1990; moulted to final instar 22 Apr; photographed 25 Apr, 18mm; pupa 4 May.; 90/50B. 1, anterodorsolateral view; 2, detail of head.

FIGURE 34. Pupa Acleros mackenii instabilis collected as penultimate instar on Vigna sp., Shimba Hills, Kenya, 15 Apr 1990; pupa 4 May; photographed 7 May, 16mm; adult 18 May; 90/50B, anterodorsolateral.

FIGURE 42. Ovum of Andronymus caesar philander collected on unidentified sapling, Lower Meru Forest, 2 Apr 1990; photographed 4 Apr; 90/32.