Investigative studies into the interspecific hybridization of Boophilus annulatus and B. microplus and its feasibility as a sterile male control technique

Abstract

Interspecific crosses between Boophilus annulatus (Say) and B. microplus (Canestrini) produced viable progeny in which all males were sterile, and females were fertile. Backcrossing F(,1) females to purestrain R. annulatus and b. microplus males produced sterile males and fertile females. Production of sterile males continued through three generations (F(,1), Backcrosses I and II). Some fertility was observed in hybrid males in the fourth generation and hybrid male fertility equaled that of purestrain ticks by the seventh generation. Statistically significant differences were observed between hybrids and purestrain controls in engorgement periods, replete female weights, preoviposition periods, egg mass weights, and percent hatch. Sterility of hybrid males was segregated out of the population by continued backcrossing, suggesting that the sterility was caused by a chromosomal incompatibility. Daily observations of B. annulatus and B. microplus males confined on stanchioned bovines determined that the average premating period was 2.6 (range 0.06-4.5) and 3.3 (range 2.5-6.5) days, average longevity was 36.9 (range 10-64) and 42.0 (range 20.5-61.5) days, and the average number of females mated was 7.5 (range 2-12) and 10.8 (range 5-18), respectively. Female B. annulatus and B. microplus were confined without males; 71.6% and 76.9% fed to repletion, and of those engorging 91.1% and 72.7% oviposited, respectively. Only 0.01% of these eggs hatched and larvae were short lived. Hybrid larvae confined in small cages in field plots survived longer than purestrain larvae. When purestrain and hybrid ticks were confined together on bovine hosts they were observed to randomly select mates regardless of genotype. Purestrain and hybrid larvae and adults were confined in varying ratios and the number of egg masses with or without hatch increased as expected with equal mating in all but two ratios as indicated by Chi-square analyses. It was concluded that hybrids were as competitive as purestrain controls under the conditions tested.