Efeito de fungos entomopatogênicos em Periplaneta americana
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2011-12-09
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Universidade Federal de Goiás
Resumo
Periplaneta americana is a synanthropic cockroach that carries pathogens, contaminates food
and the environment, and causes severe health problems, such as recurrent episodes of asthma
and other allergies, especially in children. Actually, the control of this pest is difficult due to
acquired multiple resistance to chemical insecticides and the ineffectiveness of these products in
oothecae. Entomopathogenic fungi are used for biological control against insects of medical and
veterinary importance. However, there is little information about the effectiveness and the
potential of entomopathogenic fungi to combat P. americana. In present study the pathogenicity
of 11 fungal strains belonging to seven different genera was evaluated in nymphs of P.
americana. Fungi that caused mortality > 90% in nymphs in the first test, were assayed in
oothecae of P. americana. For the test with adults the fungus that caused higher mortality in
nymphs and oothecae was selected. Conidia were formulated in oil-in-water (Graxol® 10%) at
108 conidia/ml. Nymphs, oothecae and adults were then treated topically with 0.5 µl, 2.5 µl
and 50 µl of the formulate, at a final dose of 5 x 104 conidia/nymph, 2,5 x 105 conidia/oothecae
and 5x103, 104, 5x104, 105 or 5x105 conidia/adult, respectively, and incubated in a humid
chamber at 25 ± 1ºC and 12 h photophase. The mortality of nymphs and adults was checked
daily for 25 days and the growth of fungi on the surface of the cadavers evaluated for up to 15
days. The development of the inoculated fungus on the ootheca was assessed daily during 45
days and subsequent hatching of nymphs monitored for another 15 days. Control nymphs, adults
and oothecae were treated with the emulsion without conidia. Adults and nymphs whether
treated as adults and nymphs or nymphs hatched from treated oothecae, were fed with dry cat
food (0.5 g) (Whiskas®) and water through moistened cotton (0.1 ml) arranged in small
containers. First dead nymphs were observed two days after treatment with Beauveria bassiana
IP 361, Metarhizium robertsii IP 34, M. anisopliae sensu lato IP 46, B. bassiana IP 3, M.
frigidum ARSEF 4561 and Purpureocillium lilacinum IP 320. Beauveria bassiana IP 361, M.
robertsii and M. anisopliae caused mortality in more than 80% of the tested nymphs. The other
fungi tested caused less than 20% mortality in nymphs. In adults mortality depended on the dose
and did not differ between the sexes. The inoculated fungus began to grow distinctly on the
cadavers three days after incubation of dead nymphs and adults in a humid chamber. Testing
activity of IP 34 and IP 46 in oothecae, mycelium grew on the surface of the treated ootheca 11
days after incubation and new conidia were formed at ≥ 20 days. In 31% of oothecae treated
with IP 46 and 23% treated with IP 34, oothecae had shrunk and no nymphs had hatched. In
all controls and oothecae treated with conidia, nymphs began to hatch 33 days after
incubation. All hatched nymphs survived for the following 25 days. M. anisopliae, M.
robertsii and B. bassiana IP 361 were pathogenic to nymphs and have potential for
biological control of P. americana.
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HUBNER-CAMPOS, Rayssa Fátima. Efeito de fungos entomopatogênicos em Periplaneta americana. 2011. 59 f. Dissertação (Mestrado em Medicina Tropical e Saúde Publica) - Universidade Federal de Goiás, Goiânia, 2011.