Rhabditis spp., in the Espírito Santo, State of Brazil and evaluation of biological control

Abstract The objectives of this study were to describe occurrences of Rhabditis spp. causing parasitic otitis in dairy cattle of Gir breed in the state of Espírito Santo, southeastern Brazil, and to evaluate the biological control of this nematode using the nematophagous fungi Duddingtonia flagrans (AC001) and Monacrosporium thaumasium (NF34). After nematode detection and collection, three groups were formed: two groups that were treated, respectively, with the fungal isolates; and a control group, without fungus. The treatments were as follows: (a) Petri dishes containing the culture medium 2% water agar (WA) + 250 nematodes + AC001; (b) Petri dishes containing 2% WA + 250 nematodes + NF34; and (c) Petri dishes containing only 2% WA + 250 nematodes. After seven days at 27 °C the treatments with fungi were able to capture and destroy the nematodes, with percentages of 82.0% (AC001) and 39.0% (NF34) in relation to the control group. The results demonstrate the occurrence of Rhabditis spp. after animals physical examination and that there was efficacy of the in vitro predatory activity of both fungal isolates. Thus, these results are important because they can assist in future in vivo control of this nematode in cattle.

摘要
本研究旨在描述巴西东南部圣埃斯皮里图州（Espírito Santo）吉尔牛（Gir breed）乳牛群中引发寄生性外耳炎的杆线虫属（Rhabditis spp.）的发生情况，并评估食线虫真菌鞭毛顶囊孢霉（Duddingtonia flagrans，AC001）与厚垣孢单顶孢霉（Monacrosporium thaumasium，NF34）对该线虫的生物防治效果。
在检测并采集到目标线虫后，实验共分为三组：两组分别使用上述两种真菌菌株进行处理，剩余一组为不添加真菌的空白对照组。具体处理方案如下：(a) 含2%水琼脂（WA）培养基、250条线虫+AC001菌株的培养皿；(b) 含2% WA培养基、250条线虫+NF34菌株的培养皿；(c) 仅含2% WA培养基、250条线虫的培养皿。
于27℃条件下培养7天后，添加真菌的处理组可成功捕获并杀灭线虫，相较于对照组，AC001与NF34的线虫杀灭率分别为82.0%与39.0%。
研究结果表明，经动物体格检查确证存在杆线虫属（Rhabditis spp.）感染，且两种真菌菌株均表现出良好的体外捕食活性。综上，本研究结果具有重要意义，可为后续开展该线虫在牛体内的生物防治提供参考依据。