Herbivory on bracken (Pteridium spp.) by Bolax palliata Burmeister (Coleoptera: Scarabaeidae), a poliphagous beetle of the Venezuelan Andes

Herbivoría en el helecho macho (Pteridium spp.) por Bolax palliata Burmeister (Coleoptera: Scarabaeidae), un escarabajo polífago de los Andes venezolanos

SCIENTIFIC NOTE

Herbivory on bracken (Pteridium spp.) by Bolax palliata Burmeister (Coleoptera: Scarabaeidae), a poliphagous beetle of the Venezuelan Andes

Herbivoría en el helecho macho (Pteridium spp.) por Bolax palliata Burmeister (Coleoptera: Scarabaeidae), un escarabajo polífago de los Andes venezolanos

Jorge L. Avila Núñez^I; L. Daniel Otero^II; Marlene Naya^I; Maria P. Calcagno-Pisarelli^I

^IGrupo de Química Ecológica, Depto. Química. Facultad de Ciencias, Univ. de Los Andes, Mérida 5101, Venezuela; [e-mail]

^IILab. Ecología de Insectos, Depto. Biología. Facultad de Ciencias, Univ. de Los Andes, Mérida 5101, Venezuela

ABSTRACT

Herbivore attack by Bolax palliata Burmeister is reported on two sympatric bracken species: Pteridium caudatum (L.) Maxon and P. arachnoideum (Kaulf.). Laboratory and field observations revealed a preference for the last of the two species. Available phytochemical information suggests it could be based on differences in concentration of condensed tannins.

Key words: Feeding preference, Neotropical Rutelinae, Geniatini, condensed tannin

RESUMEN

Se reporta la herbivoría de Bolax palliata Burmeister sobre dos especies simpátricas del helecho macho: Pteridium caudatum (L.) Maxon and P. arachnoideum (Kaulf.). Observaciones de laboratorio y campo mostraron preferencia por la última de estas especies. La información fitoquímica disponible sugiere que esta selección podría estar basada en diferencias en la concentración de taninos condensados.

Palabras Clave: Preferencia alimentaria, Rutelinae Neotropicales, Geniatini, tanino condensado

Insect herbivory on bracken has been a matter of special interest for several decades. Allegedly, its diverse secondary chemistry and other attributes explain its success as one of the world's most important weeds (Alonso-Amelot 2002). Different coleopteran herbivores have been documented in past accounts. Lawton (1976) reported frequent predation by Phylloperta horticola L. (Scarabaeidae: Rutelinae) in the British Isles. Kirk (1982) reported sixteen species in the Cerambycidae, Chrysomelidae, Curculionidae and Scolytidae out of a community of thirty insect species associated with bracken in New Guinea. Gilman & Cooper-Driver (1998) report Popilia japonica Newman (Scarabaeidae: Rutelinae) in Vermont, U.S.A. In the Neotropics, reports of Coleoptera or other insect herbivores are rather rare. Salinas & Ortega (1990) found Epitrix sp. (Chrysomelidae) and unidentified scarabaeids and curculionids on Pteridium aquilinium (L.) Kuhn., but did not confirm herbivory. Martins et al. (1995) reported damage on stems by curculionids and cerambycids on the same species.

This account is the first report of a massive attack by Bolax palliata Burmeister (Geniatini) on fronds of Pteridium arachnoideum (Kaufl), first observed by the first author on May 30^th, 2007, in Cerro La Bandera at 1900 m.a.s.l., near La Hechicera, North-West of the city of Mérida, Venezuela. The Geniatini includes 327 species inhabiting the Neotropics. Bolax comprises 42 known species occurring from Nicaragua to Northern Brazil (Jameson & Hawkins 2005) on different plant groups including Euphorbiaceae (Croton spp.), Mimosaceae (Inga spp.), Bombacaceae (Bombax spp.) and Lamiaceae (Hyptis spp.). Species have also been reported on cultivated fruit trees (Prunus sp., Malus sp.), on vineyards (Vitis spp.) and grasses (Jameson, pers. com.).

In Venezuela, B. palliata is considered an important pest of fruit trees, cultivated timber and natural forests (Briceño & Hernández 2004). Briceño (1989) reported intense skeletonization of Inga spp. trees in shaded coffee plantations, sometimes leading to complete defoliation.

Two species of bracken coexist at Cerro La Bandera: Pteridium caudatum (L.) Maxon and Pteridium arachnoideum (Kaulf.). The occurrence of large numbers of male and female B. palliata on the fronds of P. arachnoideum – aggregates of two to five individuals per frond, frequently in copula – as well as the evident signs of herbivory, suggested an obvious preference for this species over P. caudatum. Many pinnae in the fronds of P. arachnoideum showed conspicuous bites on the margins of the laminae (Fig. 1), which occasionally led to the loss of the frond's segment. Old damage showed the characteristic pattern of bites plus a dark brown necrosis of the remaining tissue. In order to confirm the use of Pteridium spp. as hosts by B. palliata, three subsequent sets of six male and six female beetles were confined in a glass cage and provided with one mature pinna of P. caudatum and one of P. arachnoideum. The presence-absence of beetles, or signs of herbivory on each of the bracken species were recorded after a period of 48h. In all trials, all individuals were recurrently found perching on P. arachnoideum by the end of the experiment and only the pinnae of this species had been consumed by the beetles. After copulating while on the fronds of P. arachnoideum, females dig shallow tunnels in the soil to oviposit. Larval development occurs underground.

In order to confirm herbivore preference for any of the two coexisting species of bracken in the field, two study lots, A (≈115 m²) and B (≈131 m²), were defined on the sole judgement that fronds of both species were growing in abundance. The study lots were visited on June 18^th and 20^th, 2007. In a nearly exhaustive assessment of the fronds of each species, we recorded presence/absence of B. palliata, and characteristic signs of herbivory. Of all fronds of both species, 90% had reached their fourth stage of development (following Alonso–Amelot et al. 1999) in both study lots. In study lot A, 177 of a total of 231 fronds (76.6 %) belonged to P. caudatum. Notwithstanding, only two fronds of this species (1.1%) as compared to 17 of the 54 fronds belonging to P. arachnoideum (31.5%) had B. palliata perching on them. Signs of herbivory were clearly greater in fronds of P. arachnoideum (90.7%) (P < 0.001, Chi-Square Test).

In study lot B, P. arachnoideum was dominant over P. caudatum. A number of 89 fronds (55.3%) against 72 (44.7%) were examined for signs of herbivory by B. palliata. We found no beetles at the time of our visit, but our assessment of past herbivory showed a similar overall pattern to that of lot A. Fifty fronds of P. arachnoideum (56.2%) had been feed upon, whilst only seven fronds of P. caudatum (9.7%) showed signs of Bolax herbivory (P < 0.001, Chi-Square Test).

A recent comparative analysis of the chemistry of the two bracken species (Alonso-Amelot et al. 2004) revealed important differences in content of condensed tannins in the fronds. Concentration in P. arachnoideum is nearly three times that of P. caudatum, suggesting a possible phytochemical base for the preference of B. palliata for the first of the two species. Interestingly, one more plant species in the locality was serving as a host to B. palliata adults. We observed intense feeding on a young Inga sp. tree neighboring our study site. The aforementioned record by Briceño (1989) and this confirming observation lends additional support to our hypothesis, since some Inga species are known for their high contents in condensed tannins (Koptur 1985, Galindo et al. 1989, Myster 2002), a group of compounds commonly known as defensive, due to their alleged antinutritional properties (Balick et al. 1978, Tempel 1981, Forkner et al. 2004).

Acknowledgments

Miguel Alonso-Amelot made helpful suggestions for the discussion. Mary Liz Jameson provided information on natural history and taxonomy. B. palliata was identified with the aid of Luis José Joly and Antonio D'Ascençao. Voucher specimens were deposited at the Museo del Instituto de Zoología Agrícola of Universidad Central de Venezuela (MIZA-UCV) and at the Insect Collection of the Laboratorio de Ecología de Insectos of Universidad de Los Andes, in Mérida. We also thank the financial support of CDCHT of Universidad de Los Andes of Mérida, Venezuela, Grant Nº C-1370-06-03-B.

Received 14/II/08. Accepted 11/IX/08.

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Publication Dates

• Publication in this collection
  16 Jan 2009
• Date of issue
  Dec 2008

History

• Accepted
  11 Sept 2008
• Received
  14 Feb 2008