Efeito da utilização de óleo de nim (Azadirachta indica) por via dérmica e da moxidectina por via subcutânea na prevenção de infestações artificiais por Dermatobia hominis (Linnaeus Jr., 1781) (Diptera: Cuterebridae) em bovinos

Abstract

Dermatobia hominis, the human botfly, has obligatory parasitic larval forms of the subcutaneous tissue of domestic animals, wildlife and man, causing nodule myiasis. Its importance for the cattle industry is related to the economic damages caused by those larvae. The conventional chemical control has facing some problems such as the accelerated development of resistance and residues in animal products. The objective of this study was to evaluate the prevention of botfly myiasis through the use of phytotherapic neen and of the moxidectin observing the capacity of interference in the evolution of parasite biology. For later infestation, third instar larvae were collected and kept in BOD at temperature of 27 ± 1°C and 10% R.U for pupation. After 24 to 31 days, emerged adults were placed in cages with Musca domestica and Chrysomya albiceps, used as a vector for oviposition of D. hominis. The vector carrying eggs were captured and placed in BOD. After 4 to 6 days, first instar larvae were maintained in BOD at 19° C, until host infestation. In the experimental lineation was used 12 male cattle free of D. hominis natural infestation. The animals were previously placed in screened stalls in the W.O. NEITZ Research Station at UFRRJ, receiving concentrated feed, grass, and water. The cattle was distributed into three groups with four animals and submitted to the treatments, being a control animal (treated with water pouredon), two animals treated with commercial products A and B of neem oil (Azadirachta indica, 2000 ppm of the active principle Azadirachtin) applied as a pour-on (50 ml for animal), and one animal treated with moxidectin 10% long action injected subcutaneously (1ml/100 kg) in the back of the ear. Each animal was infested with 30 first instar larvae (L1) on days 03, 07, 14, and 21 after treatment. The outbreak of L1 was stimulated by thermal source and larvae were transferred with a fine brush to a shaved region along the bovine back. The infestations were mapped for monitoring every two days to evaluation of efficacy and residual effect of treatments in accordance with the larval survival at different periods of infestation. With the purpose of verify possible collateral effects, were accomplished clinical and laboratorial examinations of the animals, before and 15 days after the treatments. Regarding efficacy, the neem products applied as pour-on had statistical not significant effectiveness for inhibition of larvae development. On the other hand, injectable moxidectin 10% showed 100% efficacy until day 14 and although larvae penetration was not precluded, larvae development was inhibited, but from day 21, did not inhibit the development of the penetrated larvae. The third instar larvae that developed after the treatments were collected and kept in BOD for observation of some biological parameters. It was observed that larvae from all treatments showed regular pupation, emergence of morphologically normal flies and the presence of viable postures.