Climate influences on the annual distribution of Haematobia irritans (Diptera:Muscidae) infestation in a dairy farm in Aguascalientes, Mexico

Abstract

A DAIRY FARM WITH 510 HOLSTEIN COWS IN MILK PRODUCTION, IN WHICH INSECTICIDE WAS NOT APPLIED THROUGHOUT THE STUDY, WAS VISITED WEEKLY FROM MARCH 1999 TO MARCH 2001, SELECTING ON EACH OCCASION TEN PERCENT OF THE DAIRY COWS FOR ADULT HORN FLY COUNTS ON DIRECT OBSERVATION. WEEKLY AVERAGE FLY NUMBERS PER COW WERE CALCULATED SO AS TO IDENTIFY PERIODS CORRESPONDING TO THE FIRST POPULATION INCREMENT, FLUCTUATION, SECOND INCREMENT AND DECREMENT. PEARSON'S CORRELATION ANALYSIS WAS CALCULATED (P < 0.01) BETWEEN CLIMATIC FACTORS AND TEMPERATURE, RELATIVE HUMIDITY AND RAINFALL, AS WELL AS FLY COUNTS FOR EACH OF THE POPULATION PERIODS. THE HIGHEST NUMBER OF FLIES PER COW WAS OBSERVED NEAR THE POPULATION PEAKS, IN SUMMER - FALL, BUT THIS WAS NEVER GREATER THAN 120 FLIES PER COW. ADULT FLIES WERE NOT OBSERVED FROM JANUARY TO MARCH. HIGH CORRELATION INDICES, 0.80 AND 0.85, WERE FOUND IN THE FIRST TEMPERATURE INCREASE, AND 0.68 AND 0.71 FOR RELATIVE HUMIDITY, IN EACH YEAR STUDIED. IN THE DECREASE, HIGH CORRELATION INDICES, 0.79 AND 0.80, FOR TEMPERATURE, WERE FOUND. THERE WAS NOT A SIGNIFICANT CORRELATION WITH RAINFALL. THE ANNUAL DISTRIBUTION OF H. IRRITANS INFESTATION WAS MOST INFLUENCED BY TEMPERATURE, LIMITING OR PROMOTING THE POPULATION PERIODS IDENTIFIED.