Analysis of an alternative method for the study of bromeliad-associated fauna in plants with different foliar organization

The efficiency of an alternative method of collection (by suction of water) for the study of Culicidae and Chironomidae (Diptera), Scirtidae (Coleoptera) and Coenagrionidae (Odonata) in bromeliads with different foliar architecture in a restinga at Florianópolis, SC, Brazil, was studied. The alternative method was less efficient to collect Culicidae and Chironomidae (Wilcoxon test p < 0.05) and was more efficient to Scirtidae and Coenagrionidae (Wilcoxon test p > 0.05) from Aechmea lindenii. This method was less efficient to collect insects of all groups from Vriesea friburgensis (Wilcoxon test p < 0.05). The alternative method was efficient to estimate the diversity of these insects in both species of bromeliads. The higher mobility of immature forms of beetles and dragonflies, and the availability of only one tank in Aechmea lindenii, contrasting to several tanks in Vriesea friburgensis that help the suction of these immature, probably influenced the results, which indicated that the suction method should not replace the dismantling in the study of Culicidae and Chironomidae. This method can be useful to get immature forms of Scirtidae and Coenagrionidae in one-tank bromeliads.


INTRODUCTION
Tanks constituted by bromeliads are the most frequent phytotelmata (Frank 1983).The insect fauna on these breeding places is diversified and mostly related to plant size and shape, exposition to light, and quantity of organic material in the tanks (Araújo et al. 2007).Water may be accumulated in a central tank or distributed among several small tanks, formed by leaves (Frank and Lounibos 2008).Müller and Marcondes (2006) noticed differences among the Culicidae faunas in two bromeliad species, which are differentiated by foliar architecture.
Studies on bromeliad-associated fauna have pro-2006), information on epidemiological role of plants as breeding places for mosquitoes (Varejã 2005), and have led to the description of new s (Pinho et al. 2005) mony).Each plant tank was sucked with a siphon bottle (1,000 ml) and blowed in the tank to mix the material by adding more pure water to the plants and repeating the suction.All the material was poured out in a translucent white plastic tray, in parcels small enough to see the immature forms.The insects were collected with a plastic disposable pipette.This methodology has been referred by Lozovei and Silva (1999) as an "alternative method" for the collection of immature forms of mosquitoes from bromeliads.After the suction, the whole plant was cut, put in a plastic bag, and transported to the Laboratory of Medical Entomology of the Department of Microbiology and Parasitology, Federal University of Santa Catarina, to check if additional animals were caught.
The mean quantity of individuals obtained by the alternative method (by suction) was compared to the mean quantity obtained in the bromeliads (by suction + dismantling the plant) by non-parametric Wilcoxon Test, using BioStat 3.0, (Service 1995) to check the efficiency of this method.Differences among the calculated Shannon-Wiener diversity indices were tested using t test according to Hutcheson ( p < 0.05) (Zar 1996).Insects from each type of plant were separately analyzed, due to differences among their foliar architectures.

RESULTS AND DISCUSSION
Chironomidae constituted the most abundant group, while Culicidae was the richest one.All insect species occurring in bromeliads, excepting Wyeomyia pallidoventer, were sampled by the alternative method (Table I).
For A. lindenii, the alternative method was significantly less efficient than the sucking plus dismantling method for the collection of Culicidae and Chironomi-test p < 0.05).The diversity in all insect groups was efficiently estimated by the alternative method ( p > 0.05) (Table II).
Immature forms of Culicidae and Chironomidae are truly aquatic, while those of Odonata and Scirtidae are semi-aquatic (Greeney 2001).The last two groups are more mobile in the bromeliad, walking among foliar axilles and possibly explaining the ease to collect immature of Scirtidae and Coenagrionidae by suction of A. lindenii, which has only one cavity.Since V. friburgensis has many water-containing axilles, there are more hiding places for these insects.
Some immature forms of Culicidae and Chironomidae, which are smaller and less mobile, can be hidden in the bottom of the axils, causing a low efficiency in the collection by suction of water and immature forms.Present results on the collection of Culicidae contrast with those of Lozovei and Silva (1999), which, not specifying the studied bromeliads, concluded that the alternative method could replace the traditional one.
The traditional method of collection of fauna in bromeliads, in which it is totally dismantled, may be considered as a census, because all insects are surveyed.The alternative method intends to get a sample as representative as possible of the fauna, without destroying the plant.
Although the alternative method was efficient to estimate the diversity of the four studied families, it was efficient to estimate just the abundance of Scirtidae and Coenagrionidae from bromeliads with only one cavity (Aechmea lindenii).So, the choice of the method for the study of the insect fauna in bromeliad tanks should consider insect group, foliar architecture, aim of the study, and amount of plants in the study area.Thus, the alternative method of collection represents a viable option in situations where the flora cannot be removed from the study area.

TABLE II Mean ± S.D. and Shannon-Wiener index (H) of immature forms of insects collected from Aechmea lindenii and Vriesea friburgensis in a restinga area at Florianópolis, SC, Brazil.
*Significantly different.