Resumo

MALDONADO-SIMAN, Ema et al. Horn fly (Haematobia irritans) incidence on cows sprayed with creosote-bush (Larrea tridentata (DC.) Coville) leaf extract. Agrociencia [online]. 2018, vol.52, n.3, pp.323-331. ISSN 2521-9766.

Horn fly (Haematobia irritans) is a widespread external parasite of grazing cattle; and integration of alternative biological control of this pest could help reduce the risk of resistance to chemical control. The objective of this experiment was to determine skin reaction to horn fly load on grazing dairy cattle sprayed with a 20 % creosote bush (Larrea tridentata (DC.) Coville) leaf extracts solution. To evaluate skin reaction a 10-month heifer with six paired circles marked on her skin was used, five sprays at five-day interval were applied; response variables were any harmful effect on skin and hair. To evaluate horn fly load effects there were two treatments: spraying or not of a 20 % creosote bush leaf extract, with six and seven cows for the no-spray and sprayed treatments, respectively. Five sprays at eight-day interval were applied, horn fly load was determined nine times; t tests were done for each time. Hair tips in sprayed circles turned green without harmful effects. Leaf extract sprayed cows showed from 9.5 to 68 % reduction (p0.05) in horn fly load compared to no-spray cows; however, not all the times horn fly count was registered, no-spray cows showed higher horn fly load than leaf extract sprayed cows. Spraying a 20 % creosote bush leaf extract showed some biological control of horn fly load with no skin harmful effects on grazing dairy cattle.

Palavras-chave : horn fly; Larrera tridentata; grazing cows; dairy production.

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