The Egg and Larval Stages of Nallachius Krooni Minter (Insecta : Neuroptera : Dilaridae)
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Current Research in Neuropterology. Proceedings of the Fourth International Symposium on Neuropterology . BagnBres-de-Luchon, France, 1991. Canard, M., Aspiick, H. & Mansell, M.W. (Eds). Toulouse, France, 1992. Pp. 261 - 269. The egg and larval stages of Nallachius krooni Minter (Insecta : Neuroptera : Dilaridae) Leslie R. MINTER University of the North, Sovenga, South Africa ABSTRACT The egg and the three larval instars of Nallachius krooni Minter were studied using a Scanning Electron Microscope and are described in detail. A number of morphological diffe- rences between the instars are noted. Digitifom sensilla on the maxillae and labial palps are recorded for the first time in Neuroptera. Key words : Neuroptera, Dilaridae, eggs, larvae, morphology, sensilla. INTRODUCTION Preimaginal stages of three dilarid species are at present known, viz : Nalla- chius americanus McLachlan (GURNEY1947; MACLEOD& SPIEGLER1961), Dilar turcicus Hagen (GHILAROV1962), D. pumilus Navds (MONSERRAT1988). Dr V.N. MAKARKINhas examined the larvae of D. septennionalis Navlis and has indicated (pers. comm.) that they bear a close resemblance to those of D. turcicus. Larvae of the Dilarinae have been found in soil whereas those of the Nallachiinae were collected under the bark of dead trees. Po~ov(1973) and GEPP (1984) review current knowledge of the immature stages of the Dilaridae. Nallachius krooni Minter has been recorded from Malawi, Namibia and seve- ral localities in the northern Transvaal, South Africa. Imagos have been collected between 2nd December and 7th April, from light traps in wooded savanna or dry riverine forest, where there is an abundance of dead wood. Adults were found in bostrychid tunnels in dead wood by W.A. LAMBORN(MINTER 1986). L.R. Minter MATERIALS AND METHODS Three female and 19 male imagos were captured on 7-8 February 1991 at a light trap near several fallen, dead trees in dense, dry mixed woodland on the farm Farmers Folly, Waterpoort District, northern Transvaal. The females were confined to glass vials containing dead twigs, and one laid eggs. Upon hatching, the larvae were separated from one another and placed in small flat-bottomed glass vials. They were fed daily on worker termites that had been immobilised by crushing their heads and legs with forceps. A disc of thin cardboard was placed on top of the termites to prevent them from moving while the larvae were feeding. Eggs and larvae were fixed in 2 % glutaraldehyde, dehydrated and coated for electronmicroscopy using standard procedures, and scanned using a S450 Hitachi Scanning Electron Microscope B. Larval nomenclature follows CRAMITON (1921) and ~~THYCOMBE(1925). DESCRIPTION One female laid twelve cylindrical, white eggs overnight in cracks and beneath the loose bark of a dead twig. The eggs were laid on their sides, singly or in groups of up to four and adhered slightly to the substrate. The dimensions (mm) of 10 eggs are : length 0.54 (range 0.50 - 0.57), width 0.19 (range 0.17 - 0.20). The ends of the egg are rounded and the anterior pole bears a mushroom-shaped micropylar prominence consisting of a central stalk covered by a cap. The sides of the cap pass downwards until they reach the chorion. About 14 micropyles are situated around the lower edge of the cap but are hidden from view unless the edge of the cap is raised slightly (Fig. 9). The chorion is covered by short projections in the form of papillae or longer curved ridges ; at the anterior pole they form polygonal clusters (Fig. 8) but elsewhere show no pattern of distribu- tion. The first-instar larvae hatched after 14 days via an irregular tear in the cho- rion at the anterior pole. No eggbreaker was found attached to the empty eggshell. First-instar larva Active campodeiform (Fig. 1). Measurements (mm) : base of head capsule to tips of maxillae 0.3 15 (n= 2) ; width of head capsule 0.12 (n=4) ; total length 1.5 (n=3). After hatching, the larvae fed for six days and then became immo- bile ; ecdysis occurred eight days after hatching (n= 11). The second instar emer- ged from the prothoracic region of the old cuticle which separated into two pieces at this point. Head light brown ; almost square, tapering slightly posteriorly, flattened dor- soventrally ; surface smooth, without scales or sculpturing. Subcuticular eyespots visible six days after hatching, but cuticular lenses absent. Setation as illustrated (Figs 2 & 3) ; trichobothria absent. Antennae 3-segmented. Pedicel divided into a short basal portion separated from a longer apical portion by parallel annular Nallachius krooni egg and larvae ridges of thinner cuticle that are interrupted on the medial surface (Fig. 10) ; in an area of thinner, sculptured cuticle lateral to the base of the flagellum, it bears a short, stout peg-like seta (Fig. 11). Flagellum noticeably thinner than the pedicel and half its length ; it bears several short and one long apical seta. Mandibles and maxillae as illustrated (Figs 2 & 3) ; the mandible bears a medial row of teeth at its apex (Fig. 12) ; the maxilla bears a single lateral digitiform sensillum near its apex and an apical group of peg-like sensilla (Fig. 12). Labium : mentum not clearly differentiated from the stipes (Fig. 3) ; prementum as illustrated. Labial palps 3-segmented. The apex of the terminal segment is truncated and bears a group of sensilla in an area of thin sculptured cuticle ; these include a long, thick seta, several short, peg-like setae and a low, dome-shaped sensillum. Cervix short ; can be extended or retracted into the prothorax. Thorax white, without markings ; prothorax as heavily sclerotised as the head capsule ; meso- and metathorax consist of large plates of thick cuticle bearing se- tae or groups of setae, separated by areas of thin cuticle (Fig. 1). The thin cuticle is highly folded, the folds running parallel to the edges of the thicker plates. Legs robust, the prothoracic pair more so than the others. The coxa arises from a ven- tro-lateral projection of the respective thoracic segment ; the trochanter is small, curved and overlaps the femur ventrally ; tibia and tarsus partly fused, divided ventrally by a groove (Fig. 1) ; pretarsus consists of a pair of tarsal claws, the in- ner longer than the outer and a clavate empodium, hinged halfway along its length (Fig. 13). Abdomen white ; 10-segmented ; the plates of cuticle surrounding the setae smaller than those of the meso- and metathorax, with larger areas of thin, folded cuticle between them ; terminal segment bifid, ending in two eversible processes that are attached to the substrate during locomotion. Second-instar larva Active campodeiform. Measurements (mm) : base of head capsule to tips of maxillae 0.48 (n= 1) ; width of head capsule 0.172 (n=3) ; total length 2.56 (n= 3). These larvae fed for 5-8 days and then became immobile, undergoing the second ecdysis 9-13 days (n=7) after the first. It differs in structure from the first-instar larva in the following ways : head capsule tapers more sharply to the base (Fig. 4) ; pedicel has two short basal divi- sions ; maxilla lacks lateral digitiform sensillum ; mentum and stipes clearly diffe- rentiated ; second palpomere has a short basal portion formed in a similar way to those of the pedicel ; third palpomere has three digitiform sensilla on its dorso- lateral surface (Fig. 5) ; cervix subdivided into lobes ; abdomen proportionately broader. Third-instar larva Active campodeiform. Measurements (mm) : base of head capsule to tips of maxillae 0.64 (n= 4) ; width of head capsule 0.24 (n =4) ; total length 5.42 L.R. Minter Figs 1-3. Nallachiu. krooni, fust-instar larva. 1. Newly hatched larva (setation not shown) ; 2. Head capsule, dorsal ; 3. Ditto, ventral. Nallacbius krooni egg and larvae Figs 4-7. NaNachius krooni, second- & third-instar larvae. 4. Head capsule of second instar, dorsal ; 5. Ditto, ventral ; 6. Head capsule of third instar, dorsal ; 7. Ditto, ventral. Scale 50 micrometers. L.R. Minter (n=4). These larvae fed for up to nine days and then died without attempting spin a cocoon or to pupate. FI8-11. hralhchiru hni.8. Egg ; 9. Ditto, mEcropylar prominence ; 10. Right scape and padice1 (p) of Fmt-instar larva ; 11. Left pedicel (p) and llagellurn (0 of third-ins larva. Nallachius bniegg and lam It differs in structure from the mod-instar lama in the following ways : pe- dicel has 3-4 short ha1divisions (Fig. 6) ; second palpornere bas two short basal divisions (Pig. 7) ; third palpomete has four digitifom sensilla on its dorsolateral surface ; cervix further subdivided dorsally ; abdomen quite distended, causing movements to ke slower and more laboured. Fks 12 & 13. Nakhius &#ni. 12. Lateral surface of left maxilla of fmt-instat larva, sho- wing digitiforrn sensilium (d) ;serrations at apex of right mandible (m) are also shown ; 13. Vcntral aspect of pretanus of Lhc lefk forelimb of a third-instar larva. The eggs of N. hooni are similar in shape and size to those of other species in which they are known (Pomv 1973 ; Gm1990). There are a number of morphological differences tetween the larvae of the Ihtee instars. Therefore interspecific comparisons should only be made ktwm larvae of the same instar. The ha1divisions of the pedicel and second palpornere are not true segments ; their function may be to increase the flexibility of the ap- pendage laterally. The antennae and labial palps are therefore essentially 3-seg- mented in all instars. Digitifom sensilla on the labial palps of 13. turcicw were illustrated by GHILAROV(1962 :405), although he did not identify them as such. Similar stmc- mres occur on the terminal segments of the maxillary and labial palps of larval and adult Coleoptera and have also been recorded from larval kpidoptera ; in elaterid Imae their tips can be everted by haemocoelic pressure whereas in some adult ktles this is not possible (ZACH~RUK1985).