Investigations on the allometric growth of Aradus species (Heteroptera, Aradidae)

Transcription

1 ANNALES HISTORICO-NATURALES MUSEI NATIONALIS HUNGARICI Tomus 77. Budapest, 1985 p Investigations on the allometric growth of Aradus species (Heteroptera, Aradidae) by T. VÁSÁRHELYI, Budapest Abstract Allometric growth of head length, head width, pronotal width, body length and length of the antennái joints of the Aradus species were investigated with help of bivariate analysis. Of these, relative length of antennái joints 2-4 can be primarily used for distinguishing the developmental stadia and identifying larval specimens. With 10 figures. As insect larvae in general, Aradid larvae have not been much investigated. Morphometric characters were studied so as to complete the series of attributes used in identification of the developmental stadia as well as of the species of the genus Aradus. Different larval instars have been treated or keyed by JORDAN (1932) and TAMANINI (1956 who as i n other taxa of Heteroptera e.g. SLATER (1951), SOUTHWOOD & SCUDDER (1956), SOUTH- WOOD (1956) used as primary characters the development of thoracal segments, wing pads, and Tamanini also extended his treatment to the head, apical abdominal segments and relative length of antennái joints 2 and 4. (Antennái joints of his three species grow according to similar patterns, these two joints showing the greatest and similar changes.) Descriptions of larval development useable for the purposes of this study have been given by HEISS (1979: Aradus lauri NOUALHIER, 1893), TAMANINI (1956: A. betulinus FALLÉN, 1829, A. corticaïis LINNÉ, 1758, A.pictus BAERENSPRUNG, 1859) and VÁSÁRHELYI (1978: A. ribauti WAGNER, 1955; 1979: Oeciacus hirundinis JENYNS, 1839; 1982: Aradus krueperi REUTER, 1882). The larvae of other Aradid subfamilies and especially of apterous species are hardly known. The present paper attempts to investigate allometric growth of body parts, the measurements of which are often given in descriptions but the suitability of which has not been tested, and to give an overall picture of the growth of antennái joints during postembironal development. Material and methods The data, other than published by the authors mentioned above, were taken from dry specimens deposited in the Zoological Museum, Helsinki, in the National Museum in Prague and in the Hungarian Natural History Museum, Budapest. As similar trends of antennái growth were observed in various species of Heteroptera Oeciacus hirundinis (Cimicidae) was also taken into consideration for comparative purposes. As many as possible (but never more than 20) specimens were measured and the significance of the averages were tested with Student's test. Since not the rules of growth, but simply the applicability of certain measurements or ratios were investigated though ousted in many studies by multivariate methods b i v a r i a t e a n a l y s i s w a s u s e d. Growth rate and initial growth index were calculated by the regression method from the logarithm of the values. Allometric trends are shown on graphs with linear scale, where data are given in mm. The ratio body length / head width Body length is subject to considerable change during each developmental stadium and it varies according to the state o f nourishment ( F Ö R S T E R 1953). I n Aradidae the effect o f the latter is strengthened by the well sclerotized sclerites and the developed dorsoventral musculature which are partly responsible for their flattened body. Nevertheless, measurements of 10 larvae o f the same instar provided averages significant i n all cases at a 0.01 probability level. 10 Természettudományi Múzeum Évkönyve 1985

2 Table 1. Growth ratio (r) and initial growth index (b) of allometric growth of body length, head length, pronotal width and length of antennái joints 2, 3 and 4, respectively compared to head width in 4 Aradus species. bimaculatus r b cinnamomeus r b corticalis r b ribauti r b body length head length pronotal width antennái joint 2 antennái joint 3 antenna! joint Postembrional change of body length of four species {Aradus bimaculatus REUTER, 1872; A. cinnamomeus, A. corticalis and A. ribauti) compared to that of head width is shown on Fig. 1, showing considerable similarity (see also the data of Table 1). Data of adults of further 30 Aradus species (all three subgenera represented) are also figured by filled circles. The trends of the two coincide, thus, according to Matsuda (1962) the trend of postembrional growth in body length head width ratio is determined at generic level, consequently it may not play any great rôle in identification. On the other hand, both parameres could equally be used in allometric investigations. The ratio head length / head width The length of the head is similarly plotted against the width of the head for the same species with the same result as in the previous case (Fig. 2). The two measurements change isometrically (Table 1) if growth ratios are calculated from the L 2 -adult data, however, in A. cinnamomeus, where L 1 larvae were also available, in this instar the clypeus is extremely short in connection with the undeveloped sucking apparatus thus the growth ratio seems to be high. When calculated from the second instar only, r = 0.99, b = Here again the equal suitability of both head length and head width as reference measurement was obtained. Since the width of the head is easily measured and with relative accuracy in Aradidae, it is suggested to use this measurement for comparison of growth of other body parts. The ratio pronotal width / head width Pro-, meso- and metanotum of the first instar larva are on the whole equally developed. In later instars the pronotum develops more rapidly in comparison with the others, and it is especially expressed in its width since the lateral margin in this genus is flattened and widened. The same consideration applies to the allometric growth of the pronotal width and head width as in the previous cases (Fig. 3, Table 1). Worthy of mention are the four species at the rigth side of the diagram. Three belong to the subgenus Miraradus containing species with alate pronotum, but the fourth is Aradus (Aradus) bergrothianus KIRITSHENKO, A further species of the subgenus Miraradus (oervendetes VÁSÁRHELYI, 1980) is not separated (width of pronotum 2.6 mm, width of head 0.85 mm). In spite of certain tendencies, even the subgenera do not separate in this way.

3 Allometric growth of antennái joints Since (he shape of the antenna and the relative length of the antennái joints are inavitably frequently used in identification of adult Aradidae, attempts were made to prove the suitability of the allometric growth of the antennái joints in identifying fifth instar larvae and also in distinguishing the different developmental stadia of Aradus species. The ratio of the joints to each other, to the total length of the antenna (Figs. 4-7, Table 2) and to head width (Table 1) were investigated. Figs. 4-6 constructed as the previous ones show obvious differences in growth trends (the moderately changing joint 1 was not figured). The length of antennái joints 2, 3 and 4, respectively, was plotted against head width in two species both

4 1.5 to g 0.5 Figs 4-6. Allometric growth of length of antennái joint 2 (4), joint 3 (5) and joint 4 (6), compared to head width (ordinate) in two species belonging to the betulae-group (x A. krueperi, + = A. ribauti). Imaginai values of further 8 species of the species group are marked with empty, other Aradus species with filled circles

5 Table 2. Antennái formula in different developmental stadia of 8 Aradus species and of Oeciacus hirundinis u L L t L L í Adult betulinus 13:22:19: cinnamomeus 20:20:20: corticalis corticalis krueperi : lauri pictus : : ribauti 11:21:19: : : safavi : : hirundis 7 :22:26: : : : 'Alto Adige, Italy (TAMANINI 1956) 2 Vihti, Finland belonging to the betulae-group of the subgenus Aradus. The adult values of 8 other species of this species group are marked by empty circles while the further Aradus species by filled circles. Even the graphic evaluation suggests the homogeneity within the species-group mentioned above and the heterogeneity of growth ratio or initial growth index or both within the genus. Encouraged by these, antennái formula, i. e. the ratio of antennái joints expressed as percentage of the total length of the antenna was used as one of the fundamental characters (VÁSÁRHELYI 1985) in a key constructed for the fifth instar larvae. The antennái formula is essentially a standardization of the data given by different authors in different scales for the relative length of the antenna! joints 1 to 4. Postembrional change of the antennái formula of several Aradus species was investigated (for examples see Table 2), of which three and that of a Cimicid species is graphically demonstrated (Figs. 7-10). In each case, in the first instar joint 4 was the longest amounting to almost half of the antenna. Joint 1 is generally the shortest and its relative length does net change strikingly in the subsequent stages. Either joint 2 or 3 grows more slowly, sometimes isometrically, and the other has a higher growth ratio to reach the imaginai proportions in most cases. A negative allometric growth characterizes joint 4 in each case. Less clearly but the same can be seen from comparison with head width (Table 1). Postembrional change in the antennái formula as well as the allometric growth of the antennái joints of the species investigated, when compared with e. g. width of head, provide valuable data in distinguishing the developmental stadia in elder larvae rather than in the first two instars. Here the thoracal structures also show valuable characters, however, they may not be useful in identifying the larval instars of the apterous Aradidae, many of which, contrary to the pertinent literature, do not have wing pads and exhibit yet unexplained features.

6 Figs Graphic demonstration of postembrional change of antennái formula in three Aradid and a Cimicid species (joints 2 and 4 are dotted). 7 = Aradus (Quilnus) safavi, 8 = A. (A.) ribauti, 9 A. (A.J cinnamomeus, 10 = Oeciacus hirundinis References FÖRSTER, H. (1953): Über die Ernährungsweise von Aradus depressus F. (Heteroptera: Aradidae). Beitr. Ent. 3(4): HEISS, E. (1979) : Über Aradidae von den Kanarischen Inseln und Marokko (Insecta: Heteroptera). Ber. naturw.-med. Ver. Innsbruck 66: JORDAN, K. H. C. (1932): Beitrag zur Kenntnis der Eier und Larven von Aradiden. Zool. Jahrb. Syst. 63: MATSUDA, R. (1962): Studies of relative growth in Gerridae. VI. Comparison of two species of Trepobates Univ. Kansas Sei. Bull. 43(4): SLATER, J. A. (1951): A key to the nymphs of Midwestern Lygaeidae (Hemiptera: Heteroptera). Bull. Brooklyn ent. Soc. 46:

7 SOUTHWOOD, T. R. E. (1956) : A key to determine the instar of an Heteropterous larva. Entomologist 89: SOUTHWOOD, T. R. E. & SCUDDER, G. C. E. (1956) : The bionomics and immature stages of the thistle lace bugs (Tingis ampliata H-S. and T. cardui L., Hem. Tingidae). Trans. Soc. Br. Ent. 12: TAMANINI, L. (1956): Osservazioni biologiche e morfologiche sugli Aradus betulinus Fall., A. corticalis L., A. pistus Bär. Rev. Mus. Stor. Nat. Venezia Tridentina 33(1-3): VASÁRHELYI, T. (1978): Contributions to the knowledge of the species Aradus ribauti Wagner, Folia ent. hung. 31(1): VÁSÁRHELYI, T. (1979): Adatok a fecskepoloska (Oeciacus hirundinis Jenyns, 1839) ismeretéhez (Heteroptera: Cimicidae). Folia ent. hung. 32(1): VÁSÁRHELYI, T. (1982): On the larval development of Aradus krueperi Reuter (Heteroptera: Aradidae). Folia ent. hung. 43(1): VÁSÁRHELYI, T. (1985) : Key to the fifth instar larvae of flat bugs of the Carpathian Basin (Heteroptera : Aradidae). Acta zool. hung. 31 (4): Author's address: DR. TAMÁS VÁSÁRHELYI Zoological Department Hungarian Natural History Museum Budapest, Baross utca 13 H-1088

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