The urticating apparatus in the larva of the Lappet Moth, Streblote panda Hübner, 1820 (Lepidoptera: Lasiocampidae)

2012·3.6 MB·English

by  Michel Joël Faucheux

Bonn zoological Bulletin 61(1): 129-134 July 2012
The urticating apparatus in the larva of the Lappet Moth,
Streblotepanda Hubner, 1820
(Lepidoptera: Lasiocampidae)
Michel Joel Faucheux
Laboratoire d'Endocrinologie desInsectes Sociaux, Faculte des Sciences et des Techniques,
2 rue de la Houssiniere, B. P. 92208 F-44322 Nantes Cedex 3, France.
Abstract.Amorphologicalstudyofthe urticatingapparatusinthelastlarval instarofStreblotepanda Hubner, 1820(Lep-
idoptera: Lasiocampidae)wasundertakenusingascanningelectronmicroscope. Itiscomposedoftwomeso-andmetatho-
racic crevices, accompaniedby urticating hairs, which open whenthe caterpillar is threatened. The urticatinghairs taper
at both ends and are mostly smooth but ringed on their distal part, which also features about 400 pores allowing the ur-
ticating liquid to be released.
Key words. Lasiocampidae, Streblotepanda, scanning electron microscopy, urticating hairs.
INTRODUCTION MATERIALS AND METHODS
The Lappet Moth Streblotepanda Hubner, 1820 (Lasio- Larvae ofStreblotepanda were captured at the Atlantic
campidae: Lasiocampinae) is distributed in Spain and coast ofMorocco at Essaouira in August 2005 and Oua-
NorthAfrica. In Morocco, it is a common species on the lidia in November 2008 on the foliage ofRetama monos-
plains and lower mountains ofthe Atlantic coast, the re- perma (Linne) Boissieu (Fabaceae). Their larval develop-
gion of Souss (Southwestern Morocco) and the Western ment comprises 5-8 instars (Calvo & Molina 2005). On-
and Central HighAtlas (Rungs 1981) where adults are ac- ly the last instar larvae have been collected and studied.
tive in January, June-July and October. Streblotepanda For observation with scanning electron microscopy
is an eremic species that prefers littoral, sandy and open (SEM), the mesonotum andmetanotumweredissectedand
&
scrub areas (Calvo Molina 2008). The caterpillars are isolated, dehydrated inabsolute ethanol, mounted on spec-
highly polyphagous, feeding on the leaves of different imen holders and coatedwith a thin layerofgold andpal-
plants fromabroad spectrum ofplant families such as Fa- ladium in a Jeol JFC-1100 sputter coater. Preparations
gaceae, Euphorbiaceae, Myrtaceae, Fabaceae, Rosaceae, were examined in a Jeol JSM-6400 SEM at 7 kV.
Salicaceae, Sapindaceae, Rutaceae and Tamaricaceae
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(Freina Witt 1987). InWesternAndalusia, it infests sev-
eral perennial plants of ornamental and economic inter- RESULTS
est such as the Blueberry (Vaccinium sp., Ericaceae; Cal-
vo & Molina, 2004). It has been considered a local pest The urticating retractable apparatus is composed oftwo
for lime and grapefruit and its larvae may also have an sets ofhairs locatedon the dorsal surface ofthe mesotho-
unwanted effect in nurseries when they feed on young racic andmetathoracic segments (Fig. 1). In each segment,
growing plants (Molina 1998). more than a thousand ofthese hairs are inserted in the in-
The caterpillar ofS. panda is known for its urticating ternal walls ofan integumentary fold composing a deep,
properties. The urticating apparatus has not been studied crescent-shaped crevice. At rest, the latteris retracted and
in detail so far; Calvo & Molina (2008) simply mention reveals externally only a transverse line whose edges are
thaturticating retractable organs develop beginning from lined with a few hairs. When active, the pocket opens, re-
the second instar and appear as mere cuticle differentia- vealing and spreading all the hairs it contains (Fig. 1). A
tions in the first instar. In the present study, details ofthe singletype ofurticatinghairhas been observed. It is spear-
mm
morphological structures responsible for the urticating shaped, 0.65 1.10 long (Fig. 5), with a slender base
properties are provided for the first time. (Fig. 6) and pointed distally (Fig. 7). It is delicately stri-
Received: 20.11.2011 Corresponding editor: D. Stiining
Accepted: 10.04.2012
130 Michel Joel Faucheux
Fig. 1. Larva ofStreblotepanda, last instar. Left: at rest, right: disturbed, showing the two urticating crevices.
ated longitudinally from the base onwards over 14/15 of ofthe segment (Figs. 13, 14). The white scales, which
its length (Fig. 7). The distalpart (1/15 ) comprises an area have the form of a strongly elongated tennis racket
with annular ligaments (Figs. 7, 8), tapering to the point- (some visible in fig. 3), are covered with longitudinal
ed andperforated tip (Figs. 9, 10). The estimated number ribs made up ofoverlapping elements resembling roof
ofpores per hair is about 400; their diameter reaches 0.3 tiles (Fig. 15). This structure is analogous to that of
um. The hairs are inserted in raised cupolae, from which scales found on butterflies' wings.
mm
they may be detached (Fig. 11). Five-six nonporous sensilla chaetica, 0.90-1.15
long, are found on the pair ofwhite D1 verrucae in the
Different types ofintegumentary structures are associat- anteriorarea ofthe meso- and metathorax(Figs. 16, 17).
mm
ed with the urticating apparatus: Other sensilla chaetica, 0.50 long, are found among
the urticating hairs (Fig. 18).
- Some thirty white scales, 0.30-0.35 mm long, are lined Sensilla filiformia, 1.5-2.0 mm long, are found in lat-
up along the posterior edge of each urticating pocket eral tufts on the meso- and metathorax (Fig. 16).
(Fig. 12), whereas dark scales are spread over the rest
Bonn zoological Bulletin 61 (1): 129-134 ©ZFMK
The urticating apparatus in the larva ofthe Lappet Moth, Streblotepanda Hiibner, 1820 131
Figs 2—11. Urticating apparatus ofS. panda. 2. Urticating crevice on the mesothorax, showing urticating hairs (arrow). 3. Setal
tubercle (T), urticating hairs (arrow) and scales (S). 4. Group ofurticating hairs. 5-11. Urticating hairs. 5. Entire hair (arrow). 6.
Base ofhair. 7. Tips ofhairs. 8. Tip ofhair with ringed and perforated area. 9. Detail ofthe perforated area. 10. Detail ofdistal
pores. 11. Cupolae ofurticating hairs.
Bonn zoological Bulletin 61 (1): 129-134 ©ZFMK
132 Michel Joel Faucheux
Figs 12-18. Scales, tubercles, sensilla and urticating hairs ofS. panda. 12. Scales (arrow) among urticating hairs. 13. Isolated
scales. 14. Filiform scales. 15. Detail ofscales. 16. Dorsal surface ofthe metathoracic segment showing two setal tubercles (T),
urticating hairs (arrows) and filiform sensilla (F). 17. Setal tubercle with sensilla chaetica (arrows). 18. Sensillum chaeticum (ar-
row) among the urticating hairs.
DISCUSSION (Thaumetopoeinae), these mirrors are located on abdom-
inal segments I—VIII whereas in the 3 instar ofthe same
Structure. The large number ofurticating hairs is char- species, they appear on different segments (Sellier et al.
acteristic ofurticating apparatuses (Bourgogne 1951). Un- 1975). This difference in location of defense-related se-
like ordinary long hairs, the urticatinghairs oflepidopter- tae among instars is rather unusual, given that in most
an larvae are typically not arranged at random and do not groups, as in S. panda, the position is constant through-
nd
cover the caterpillars' bodies in a uniform manner. They out the larval development. Afterthey appearinthe2 in-
&
are arrangedin verydensegroups onwell defined surfaces star (according to Calvo Molina 2008), they remain on
known as 'mirrors' that are integumentary folds (Sellier the same thoracic segments, a situation known frommany
et al. 1975) or other specific surface areas. The first lar- other species ofLasiocampidae (e.g., in the genera Den-
val instars lack urticating hairs. In the 5 larval instar of drolimus and Gastropacha). Other lasiocampid moths,
the 'brown-tail moth'Euproctis chrysorrhoea (Linnaeus) such asMacrothylacia rubi,Lasiocampa quercus and oth-
(Lymantriinae), the 'pine processionmoth' Thaumetopoea ers, are known to possess urticating hairs on the abdom-
pityocampa (Denis & Schiffermuller), and the 'oak pro- inal segments (Carter & Hargreaves 1988).
cession moth' Thaumetopoea processionea (Linnaeus)
Bonn zoological Bulletin 61(1): 129-134 ©ZFMK
The urticating apparatus in the larva ofthe Lappet Moth, Streblotepanda Hiibner, 1820 133
A single type ofurticating hairs is known in S. panda. chanical element (penetration ofthe skin and breaking of
This is also the case in most other species ofdifferent fam- the hairs caused by scratching) and a chemical element
ilies (Gilmer 1923, 1925; Faucheux 2007). However, there (discharge of a toxic substance derived from dermal
are also species that have several different types ofhairs, glands) account for the pathological symptoms. The ac-
e.g. three types in Latoia thamia Rungs (Limacodidae) tion ofthe urticating hairs is ascribable, at least in part,
(Faucheux 2000). Among the different forms ofurticat- to the secretion ofhistamine that takes place on the skin
ing hairs, the most frequent in lepidopteran caterpillars is as a result ofthe penetration ofthe poison contained in
a harpoon-shaped hair with pointed spikes directed to- the hairs (Leclercq 1977).
wards its distal end and arranged in three or four longi- In S. panda, urticating hairs are released in large num-
tudinal rows, e.g. as in T.pityocampa, T.processionea, E. bers when the caterpillar is handled. In contact with the
chrysotrhoea (Sellier et al. 1975), Lithosia quadra Lin- skin, they stick to it by means oftheir distal circular lig-
naeus (Faucheux 2007), and in one type ofL. thamia (Fau- aments, but the urticating effect seems to be low. The nu-
cheux 2000). These hairs, though hollow, are not perfo- merous pores at the distal ends ofthe hairs indicate that
rated at any extremity and therefore are unable to inject a liquid isbeing released, but direct evidence is still miss-
thetoxic substance (Sellieretal. 1975). Instead, they must ing. Previous studies do not mention strong irritations or
be broken, forexample in the skin, in orderto release their even dermatitis caused by the caterpillars of the lappet
urticating substance (Ducombs et al. 1979). moth.
In anothertype ofhair, the nucleus ofthe poison-gland
cells is located at the base ofthe hair and the cells devel- Protective function. The aposematic red and dark brown
op inside the hair. During contact, the urticating substance ofthe two urticating crevices strongly contrast with the
is released as the acute, sharp end ofthe hair breaks. This overall grey colour of the larva. Unlike other urticating
type has been described in the "urticating thorns" ofLa- caterpillars, those ofS. panda undoubtedly use their ur-
toia (= Parasa) hilarata Staud. (Mills 1925) and in the ticating apparatus mainly as a means ofwarning against
"poison apparatus" ofLatoia (=Parasa) latistriga Walk- theirpredators. To myknowledge, no study has tested the
er (Gilmer 1925). Gilmer (1923) distinguishes two types efficacy ofthis defence mechanism against natural ene-
ofpoisonous apparatuses ofwhich the one he considers mies. In the environment in which I observed the Moroc-
more primitive consists ofsimple hairs that are shorterand can caterpillars (colonies ofRetama sp.), they come in fre-
stifferthan others; each hairis connected through its prox- quent contact with likely predators such as the common
imal endto apoison glandand opens in a distal pore (e.g., chameleon, Chamaeleo chamaeleon Linnaeus and the
Orgyia leucostigma (J. E. Smith)). The structure ofthe ur- stripelesstreefrog,Hyla meridionalis Boettger, which may
ticating hairs ofS. panda may therefore be close to this hesitate to prey on the caterpillars. Similarly, children and
primitive type, as the irritating substance flows through adults are unwilling to touch a caterpillar that manifests
the numerous pores located on the distal end ofthe hair. its anxiety by opening and closing its hair slits.
Function ofthe mirrors. The mechanism foropening and Acknowledgements. It is a pleasure to acknowledge Nicolas
closingthe 'mirrors' (orcrevices) that contain the urticat- Stephant and Stephane Grolleau (Centre ofSEM, University of
ing hairs was described for T. pityocampa by Demolin Nantes, France), and Catherine Cercle for their technical assis-
(1963). In this species, the implantation zone ofthe hairs tanceas well asVittorio Ballardini forhelp withthetranslation.
is delimited by a semi-rigid frame made up ofchitinous
rods andsmall pads forming hinges. This arrangementcan
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