Ação do nematóide entomopatogênico Heterorhabditis indica LPP1 (Poinar, kranukar & David, 1992) (Rhabditida: Heterorhabditidae) sobre a biologia reprodutiva de fêmeas ingurgitadas de Boophilus microplus (Canestrini, 1887) (Acari: Ixodidae)

Abstract

The cattle tick Boophilus microplus (Canestrini, 1887) (Acari: Ixodidae) is an ectoparasite associated with various diseases that can reduce animals’ production on even cause their death. The main control method is application of carrapaticides, which can lead to resistant tick populations. Entomopathogenic nematodes have been indicated as excellent candidates for biological control of insect, and recent studies have shown their efficacy against ticks. The objective of this study was to assess the effects of the LPP1 isolate (from Monte Negro, Rondônia, Brazil) of the species Heterorhabditis indica (Poinar, Karanukar & David, 1992) on the reproductive biology of ingurgitated B. microplus females. Different nematode concentrations were tested, with 75, 150, 300, 600, 1200, 2400 and 4800 infective juveniles dispersed in distilled water per female. Each group of 30 females was separated into six Petri dishes containing sand, each with five females, for a total of eight groups including the control. The Petri dishes were then kept in a climate controlled chamber at 27 ± 1° C and UR>80%, for 48 hours. After the exposure time, the females that were still alive were placed individually in plastic cups and observed daily until the last one died. The start and end of laying was observed for females that laid eggs, and the date of death and post mortem aspect were noted for all females. The other parameters recorded were initial weight, pre-laying period, laying period, survival period, egg mass weight, change in weight and final weight of the female ticks, egg incubation period (EPI), larval hatching rate (% HR), egg production index (EIP), nutritional index (NI), and control percentage (%C). There were no differences observed in the initial weight and pre-laying period between the control group and all the treatments. There was a difference in the final weight of the control group and treated groups, but none among the treatments. In relation to female weight and nutritional index, there was a difference between the control group and treated groups, which increased as the concentration of infective juveniles went up. There was an evident reduction in the treated groups both in laying period and survival period. The egg mass and the hatching percentage were smaller in the treated groups. The egg production index was similar in the control group and the treated group with the lowest concentration, and different for the other concentrations. All the treatments with nematodes showed efficacy greater than 95% in controlling the ticks.