Abstract
Several psiculture stations that deal with fingerlings or ornamental fishes rearing have presented some problems with larvae preying, post-larvae and fingerlings by Odonata Order insect nymphs. Thus, the aim of this work was to survey the Odonata species present in fish-raising tanks in two towns of the Midwest region of Minas Gerais, and also to evaluate the effect of Bacillus thuringiensis var. Barjac israelensis on Pantala flavescens nymphs (Fabricius, 1798) (Odonata: Libellulidae). Fortnightly collections were performed over a three month period. The adult insects were captured with entomological nets and the nymphs with fine mesh sieves, coupled to wooden handles. The captured nymphs were taken to the laboratory where they were individualized in 2L plastic foam boxes and sealed in its upper extremity with tulle. Soon after the adults emergence, they were killed, packed into envelopes and sent to be identified. The laboratory experiments were conducted in an acclimatized room at 25 ± 2°C, RH of 70 ± 10% and 12-hour photophase. Second instar P. flavescens nymphs were packed individually into plastic foam boxes containing 500mL of chlorine free water each one. When they were in the third, fifth and seventh instars, they were treated with B. thuringiensis var. israelensis through the microbial product Vectobac® in granulate formulation. The product was directly applied to the rearing container water at the concentration denoted for the control of culicidae larvae, two superior concentrations, two inferior and also another one, where the product was not applied. The evaluations were done at 24, 48 and 72 hours after the product application, recording the dead insects number in each treatment. In both experiments, the nymphs were fed with Culicidae larvae and new-born fishes of the species Poecilia cf. vivipara Schneider, 1801. The following species were identified: Ischnura fluvialis Selys, 1876; Aphylla theodorina (Navas, 1933); Brachymesia furcata (Hagen, 1861); Erythrodiplax fusca (Rambur, 1842); Miathyria marcella (Selys, 1857); Micrathyria almeidai Santos, 1945; Micrathyria hesperis Ris, 1911; Orthemis discolor (Burmeister, 1839); Perithemis mooma Kirby, 1889 and P. flavescens. There were no significant microbial product effects on the studied species
Highlights
Second instar P. flavescens nymphs were packed individually into plastic foam boxes containing 500mL of chlorine free water each one. When they were in the third, fifth and seventh instars, they were treated with B. thuringiensis var. israelensis through the microbial product Vectobac® in granulate formulation
The product was directly applied to the rearing container water at the concentration denoted for the control of culicidae larvae, two superior concentrations, two inferior and another one, where the product was not applied
The nymphs were fed with Culicidae larvae and new-born fishes of the species Poecilia cf. vivipara Schneider, 1801
Summary
Os experimentos foram conduzidos na Universidade Estadual de Minas Gerais - Uemg, Campus da Fundação Educacional de Divinópolis, em sala climatizada à 25 ± 2°C, UR de 70 ± 10% e fotofase de 12 horas e em 2 estações de piscicultura, no município de Divinópolis e Itaúna. As ninfas capturadas foram acondicionadas em recipientes plásticos de 2 litros contendo água do próprio tanque e levadas para a sala climatizada, na qual foram individualizadas em caixas de isopor de 12cm de altura x 12cm de largura x 18cm de comprimento, contendo cada uma 500mL de água oriunda dos tanques onde foram capturadas. Ninfas de segundo ínstar foram individualmente acondicionadas em caixas de isopor nas mesmas proporções citadas anteriormente, contendo cada uma 500mL de água dos tanques. As concentrações utilizadas foram calculadas em função do volume de água dos recipientes, sendo essas: concentração indicada para o controle de larvas de culicídeos (1200mg), duas concentrações superiores (1600mg e 2000mg) e duas inferiores a essa (400mg e 800mg), além da testemunha, na qual não se aplicou o produto. Nos ínstares onde se aplicou o produto, as ninfas foram alimentadas somente com os peixes, sendo que nos demais adicionou-se larvas de Culicidae. O delineamento experimental foi inteiramente casualizado, com 6 tratamentos (5 concentrações do produto microbiano mais a testemunha) e 20 repetições, cada uma constando de uma caixa de isopor contendo uma única ninfa do inseto, conforme citado anteriormente
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