Zenonia zeno Trimen, 1864,
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: 7-11
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|Zenonia zeno Trimen, 1864|
This is a common and widespread species described from South Africa ( Trimen 1864) and found north to Ethiopia and west to Nigeria ( Evans 1937 a). In Kenya, it is common in upland areas; I have many observations from around Nairobi, and have seen it east to Thika and west to Kakamega, and on Mt Kenya above Chogoria. Van Someren (1939) reported it as abundant in the Chyulu Hills, but Sevastopulo (1974) does not record it from the Shimba Hills. In Tanzania it is found a long forest edges and streams through most of the country excluding coastal areas.
Van Someren (1939) refers to it in the Chyulu Hills as “very abundant in the grass lands and in the forests where certain grasses were growing and on which the larva feed”. Van Someren (1974) lists the food plants as grasses including cultivated sorghum ( Sorghum bicolor ) and maize ( Zea mays ). Sevastopulo (1975) gives grasses for Z. crasta Evans (see under Zenonia above) in his list of the food plants of East African Macrolepidoptera, but since he didn’t rear this species (Sevastopulo unpublished), no one else has reported food plants for Z. crasta , and it is immediately preceded by Z. zeno in his list without an entry, it seems likely that he intended Z. zeno . Later he adds records for Z. zeno of sorghum and maize ( Sevastopulo 1981), probably based on Van Someren (1974). MJWC has found this species something of a generalist grass feeder, and reared it from caterpillars collected on Cenchrus trachyphyllus (= Pennisetum trachyphyllum ), Cynodon nlemfuensis , Megathyrsus maximus (= Panicum maximum ), Panicum deustum , P. m o n t i c o l a, Setaria megaphylla (= S. plicatilis ), Zea mays (maize) and at least two other unidentified grasses. S.C. Collins has also reared it from maize in Nairobi, Kenya ( ABRI). TCEC found it on a bamboo, Arundinaria alpina , in Mufindi, Tanzania.
Ova are laid usually singly on the leaves of the food plants, and the newly hatched caterpillars eat all the shell except the base. They are dome-shaped with a narrow flange around the base. The base of one associated with a first instar caterpillar that was successfully reared measured 1.2mm in diameter with the flange and 1.1mm without it.
On the large, broad leaves of Setaria megaphylla , all stages of the caterpillar make a roll at the apex of the leaf and feed basally to this (87 /36, 88/ 80). The medium sized leaves of Panicum deustum are treated similarly, but the fifth instar caterpillar, because of its weight, causes the distal section of the leaf with the shelter to droop (90 / 102). On maize leaves, the shelter is also at the tip, but the shelter is rolled upwards, rather than downwards (88 / 121). The leaves of P. monticola are short and broad, and the mature caterpillar uses an entire leaf to make its shelter, holding the edges together with a few strands of silk (87 / 30). In contrast, the thin leaves of Cynodon nlemfuensis suit the small caterpillars which can roll the edges upwards up to make a narrow tube before or at the leaf apex, and feeding is basal to the shelter (88 /107, 88/111, 89/ 54). However, fourth and fifth instar caterpillars may need to draw two or more leaves together to gain adequate shelter.
There are five instars—I have reared this species from the first instar three times. The first three instars have black shiny heads, widest near the base; body green with a darker dorsal line defined by a pale sub-dorsal line on each side. The heads measure 0.6 x 0.6 (n= 3), 0.8 x 0.9 (n= 5), 1.2 x 1.3mm (n= 7) wide x high. In instar 4, the head is normally shiny black in males, although in one example the epicranium showed a trace of a pale band. In contrast, females are more or less extensively marked with pale brown ( Figure 7View FIGURE 7). Instar 4 heads measure 1.7 x 2.0mm wide x high, those of the female slightly larger (1.8 x 2.1mm vs. 1.7 x 1.9mm); body dull, dark green; pale broad subdorsal line; narrow pale dorsolateral and lateral lines, the latter running through the spiracles, which are pale; T 1 and all legs concolorous (ref. 88 / 80).
The final instar measures up to 36mm, and has a rather distinctive head ( Figure 8View FIGURE 8), which measures 2.1 x 2.8mm (n= 12) wide x high, the female being slightly larger (2.1 x 3.0mm compared to 2.1 x 2.7mm). The following description is based mostly on a caterpillar collected on Panicum monticola in Ololua Forest, beside Karen, Nairobi (ref. 87 / 30). Head translucent, whitish; pale brown or slightly green translucent stripes along epicranial suture and adfrontal sutures, down each side of face, and a broad stripe running from the vertex laterally to behind the stemmata ( Figure 8View FIGURE 8); stemmata black; mouthparts brown. T 1 dorsal plate not obvious. Body translucent, whitish with a yellow tint dorsally, especially on the creases on the posterior margin of each segment; fine white reticulate network in dorsal half of body, except dorsal line which is broad, mostly clear with just a few translucent dots; white slightly diffuse subdorsal line; narrow white dorsolateral line sharper due to slight concentration of darker dots adjacent; spiracles white, inconspicuous; body less white in ventral half from just below spiracles; dorsal, subdorsal and dorsolateral lines extend onto anal plate which has an obvious fringe of white setae. In the mature caterpillar rectangular white wax glands develop on the ventral part of segment A 7 –A 8, that on A 7 longer along the line of the body, while that on A 8 is longer transversely (88 / 108 C). This distinctive final instar caterpillar supports the separation of Zenonia from the other grass feeding genera of Baorini , but the pupa suggests its affinity to the genera that follow. Instars 2 to 5 take 6 (n= 2), 8 (range 6–11, n= 6), 9 (6–17, n= 9) and 14 (11–20, n= 11) days respectively.
Pupae collected from Cenchrus trachyphyllus at Nairobi (90 / 80), and on similar unidentified grass at Thika, were formed under a leaf, approximately at the point of flexion so that the leaf provided some overhead protection. The shelter was minimal—the edges had been pulled slightly together and held with silk before and after the pupa, but from below the pupa was fully exposed.
The pupa ( Figure 9View FIGURE 9) is similar to those of Pelopidas spp. and Borbo spp. and typical of many grass feeding skippers. The pupa (87 / 30) measured 27mm long by 5mm wide, and the elongate but blunt frontal spike was 2–3mm wide at the base; the cuticle is transparent, so that the developing colouration can be seen through it (Figure 9.2); ground colour dull whitish green; four narrow yellow-white dorsal and subdorsal lines run from near the front of the thorax to just short of the cremaster, about 1 mm apart. The proboscis extends beyond the wing cases, but stops short of the cremaster by about 2mm. The frontal spike may be slightly upturned (89 / 76). Pupation takes 15 (13–18, n= 14) days, and so the whole life cycle might take about 2 months.
This species is attacked by an euplectrine, which I have reared from parasitized small to medium sized caterpillars or from pupae associated with similar caterpillar corpses in leaf shelters on Cynodon nlemfuensis (87 / 107 H), Panicum deustum (90 / 95) and Megathyrsus maximus (or similar grass) (91 / 16) around Nairobi and at Thika. Second or third instar caterpillars were associated with 1–3 parasitoid pupae. Metisella quadrisignatus (Butler) ( Heteropterinae ), and probably other grass feeding Baorini , are also parasitized by a euplectrine, probably the same species, and as the young host caterpillars are all green with black heads, observations need careful interpretation.
Figure 6.3 shows an adult that has been caught by a crab spider. Although a variety of predators must feed on adult Hesperiidae , it is rarely that one sees an actual predation event. I have observed crab spiders as occasional predators of Hesperiidae in South America ( Cock 2003, 2012) and Africa, so probably they are a significant mortality factor for adult butterflies.
Although the earlier instars of this species are similar to those of other grass-feeding Hesperiinae and Heteropterinae in Africa, the mature caterpillar is distinctive. The pupa resembles those of Pelopidas and Borbo .
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