Bionomics of Sabethes chloropterus Humboldt, a vector of sylvan yellow fever in Middle America.

Abstract

Summary A colony of S. chloropterus was established in 1-meter cubical cages. A trussed guinea pig or rhesus monkey served as the source of blood for the females, while a cotton ball soaked in sugar solution and hung from the top of the cage made available the necessary carbohydrates for both males and females. A well-ripened section of bamboo closed with a lid and with a 1-inch hole through its side was used as an oviposition receptacle. Larvae were reared in round enamel pans 10 inches in diameter in a yeast-infusion medium. S. chloropterus was found to be strictly diurnal in habits. Females seek a blood meal in greatest numbers during the early afternoon hours (1400–1500). Both males and females become engorged on sugar solution from 6 to 24 hours after emergence. No female has been observed feeding on blood before the fifth day after emergence and the peak of biting activity is not reached until the second or third week. Females prefer to bite high on the body having a special predilection for the nose and lips. S. chloropterus is a stenogamic species. Mating occurs while resting on a surface and is preceded by peculiar prenuptial activity on the part of the males. Copulation lasts from 4 seconds to 34 minutes, with an average time of 6 minutes. Mating has not been observed before the sixth day after emergence and the peak of mating activity is not reached before the second or third week of the female's life. Insemination does not necessarily occur before the first blood meal and does not appear to be essential for ovarian development. Females oviposit by hovering in front of the hole in the bamboo section and forcibly ejecting one or two eggs through the hole and into the water in the bamboo. The position of the sun in the sky rather than light intensity seems to be the determining factor in inducing oviposition. The greatest percentage of eggs are laid in early afternoon (hours 1200–1500). The species was found to be nonautogenous, that is to say, it must have a blood meal before egg-laying takes place. Oviposition usually begins on the third day after a blood meal and goes on through the thirteenth day. The average number of eggs per female after a single blood meal is 38.6 with a minimum of 2 and a maximum of 103. Each female may lay an average of 138 eggs during her life time. Females exercise a definite preference for ovipositing in a bamboo with closed top and a 1-inch hole through the side rather than in a bamboo with open top. The eggs of S. chloropterus are rhomboid in shape, the embryo develops in 3 to 4 days at room temperature and the eggs hatch soon after the larvae attain full development inside, being incapable of going into a prolonged diapause. The larvae are facultatively predaceous and cannibalistic but they do not frequently attack larvae of their own species, when in the same stage of development. They do not swallow the prey but suck the body contents through punctures in the cuticle. The mean period spent by larvae from hatching to pupation at 26°C, is 14.8 days with a maximum of 28 days and a minimum of 9 days. The mean developmental period of pupae at this temperature is determined to be 150 hours with a maximum of 160 hours and a minimum of 123 hours. The mean life span of females after the initial blood meal at mean temperatures of 26.1 to 26.8°C and a mean relative humidity of 92 to 97%, was found to be 38.9 days with a maximum of 140 days. It was also determined that 50 per cent of these females live between 5 and 6 weeks after taking their first blood meal and that 9 to 10 weeks elapsed before 90 per cent of these females died.