Metisella midas subsp. midas Butler 1894

Metisella midas midas Butler, 1894

This subspecies was described from Zomba, Malawi (Butler 1894), and its range extends from Malawi and Zimbabwe to Congo and East Africa. Evans (1937) described specimens from Nigeria and Cameroon as subspecies malda. This species is one of a group of four orange spotted Metisella spp. from Kenya. It can be distinguished from the other species by the presence of a basal spot in the cell of the hind wing upper side (Figure 1.1). It is associated with swampy areas and is widespread in Kenya in such areas. MJWC found a colony in the swampy ground adjacent to the stream at the bottom of his garden in Kyuna Estate, Nairobi at an altitude of 1750m. Here a few specimens could be found at any time of year, breeding on a swamp grass, Leersia hexandra.

Adult behaviour. The adults are active in sunshine, flying low over the swamp vegetation, settling on leaves and flowers. Sunbathing occurs occasionally with wings held three-quarters open (Figure 1.1), or as once observed with the wings held together, but with one forewing much lower than the other (Figure 1.2).

Food plants. MJWC found caterpillars only on Leersia hexandra, a fine-leaved grass common in swampy areas around Nairobi (Larsen 1991, Cock & Congdon 2012).

Ovum. The ovum (Figure 2.1) is small, white and hemispherical, 0.64mm in diameter (n=2) and 0.44mm high (n=1). Ova are laid on the food plant leaves, usually in slightly shady situations near the top of the swamp vegetation. They turn darker as they mature.

Leaf shelters. The smallest shelters are made with the apical portion of a leaf which is rolled upwards (or occasionally downwards), with feeding basal to the shelter. Larger caterpillars form a similar shelter from a middle section of the leaf (Figure 2.2) and caterpillars feed basally or distally to the shelter. The final instar caterpillars make a minimal shelter for pupation by flexing the leaf edges downwards and holding them by a couple of strands of silk at each end. This flimsy shelter does not protect the caterpillar which drops out readily, but the narrowness of the leaves and the fact that they seldom grow closely together means that there will be few opportunities for a caterpillar of this size to make a more substantial shelter (cf. Figure 2.5 to compare caterpillar with leaf).

Caterpillar. There are five instars. Instar 1 is green with a brown, shiny head, measuring 0.4 x 0.4mm wide x high (n=1). Instar 2 has a dark brown, shiny head, 0.55 x 0.6mm wide x high (n=3); pronotum black; body green with indistinct pale stripes.

The instar 3 caterpillar measures 7mm when newly moulted (89/80 A); head 0.8 x 0.9mm wide x high (n=6); brown, shiny, weakly rugose; diffuse paler band parallel to epicranial suture and adfrontal suture to stemmata; upper adfrontals diffusely pale; epicranial and adfrontal sutures dark; inconspicuous short brown setae. Another individual (90/6F) had the head uniformly brown. Pronotum dark; body green with pale stripes; anal plate with brown tint; short, pale brown setae on body, longer and darker on pronotum, A 7–9 and anal plate.

The head of the instar 4 caterpillar (Figure 2.4, 89/80 A) measures 1.05 x 1.3mm wide x high (n=4); light green-brown, with a brown stripe along epicranial and adfrontal sutures, and from vertex, over apex, anterolaterally to stemmata; posterior margin narrowly dark. In the case of individual 90/6F the brown stripes are darker and extend onto upper lateral part of adfrontals (Figure 2.3). T1 concolorous with body; body green with pale stripes; short pale setae.

The final instar caterpillar (Figure 2.4–6) is 20mm long; head 1.7 x 1.9mm wide x high (n=2), relatively small compared to body; the head of most individuals were dull green, slightly brighter on the face; moderately rugose; stemmata dark. In the case of individual 90/6F the head was dull matt green, with dark lines along the adfrontal sutures and from apex, anterolaterally to stemmata. T1 and pronotum concolorous with body. Body dull green; pale stripes from T1– A 9; dorsolateral line strongest, especially on T1–T3 and A 7– A 9; two pairs of dull greenish white subdorsal lines, united into one line on T1–T2; indistinct line just below dorsolateral line; lateral tracheal line visible through cuticle; spiracles pale, inconspicuous; all legs concolorous; short, pale setae on body; longer pale setae with a few darker ones on anal plate.

Pupa. The pupa (Figure 3) is formed in the final leaf shelter attached at the cremaster and supported by a single strand girdle of silk; because the shelter is so flimsy the pupa must rely on camouflage to avoid detection. Pupa 17– 18mm, including 2.1mm (n=2) frontal spike, 1.0mm wide at base (n=2); the cuticle is translucent, so pupal colouring reflects the contents (89/9 A); head, thorax and appendages bright matt green; abdomen whitish green, slightly shiny; a narrow, dark, dorsal line from tip of spike to tip of cremaster; narrow white dorsolateral line from anterior margin T2 to tip of cremaster, diverging smoothly to A 4– A 5 and converging just before final segment where it follows the edge of the segment; faint, intermittent, very narrow dark line below dorsolateral line from eye to tornus fore wing, with a conspicuous dark dot in line on T2; very indistinct white lateral line on abdomen; spiracles pale brown, inconspicuous. Pupation takes 14 days.

Natural enemies. At Kyuna Estate, Nairobi, the ova are attacked by an unidentified egg parasitoid. An ovum collected 20 Oct 1988 yielded a solitary parasitoid (88/97B). An ovum from which a parasitoid had emerged was found 14 Jan 1990 (90/3C); the emergence hole was 0.3mm diameter at the widest.

Caterpillars are parasitized by what appears to be two species of Elasmus (Eulophidae): one metallic green with pale legs and antennae, the other darker, with dark antennae and banded legs (referred to here as Elasmus sp. green and Elasmus sp. dark respectively) (Table 2).

Elasmus sp. Ref. Date of Host remains Parasitoid Date of Date adults Number of collection collected pupation emerged adults The number of Elasmus spp. larvae per paralysed host caterpillar varies from one to three probably linked to the size of the host caterpillar and the number of Elasmus sp. larvae which it can support to complete development. The Elasmus spp. larvae feed as small external grubs, absorbing nourishment through the host skin, before pupating as small naked shiny black (initially white) pupae in the host shelter. The adults emerge after a further 8– 10 days.

Caterpillars parasitized by a Meteorus sp. were collected 16 Mar 1989 (89/10 A, final instar), 14 Jan 1990 (90/ 3B, final instar) and 30 Jan 1990 (90/6F, collected as instar 3; Meteorus sp. larva emerged from final instar); a cocoon with no host remains was collected 14 Oct 1989 (89/80). The parasitoid larva emerges from the final instar caterpillar by boring a hole through the cuticle, usually on the underside of segment A 7. It spins a rough brown cocoon, slightly pointed at each end, measuring about 6 x 2mm, often in the host leaf shelter. The host remains often stay in the leaf shelter and may be responsive for several days after emergence of the Meteorus sp. larva. Emergence from the cocoon takes place after 12–13 days.