The safety of Bacillus species as insect vector control agents.

One of the success stories of international co-operation in the control of infectious diseases has been the World Health Organization’s (WHO) Onchocerciasis Control Programme (OCP) in West Africa; the use of Bacillus thuringienszs (BT) toxins has been an important component of the programme (Rurges 1981; Anon. 1987; Guillet 1990; Webb 1992; Drobniewski 1993a). Onchocerciasis, or ‘river blindness’, is a chronic filarial disease caused by the parasitic nematode worm Onchocerca volvulus, and is transmitted by blackflies of the Simulium genus. The WHO estimates that over 90 million people are at risk from acquiring the disease, that there is an overall prevalence of 18 million people and that 1 000 000 cases of blindness have been caused by onchocerciasis (Anon. 1987; Guillet 1990; Webb 1992; Drobniewski 1993) . I t is a significant preventable cause of blindness and two disease control strategies have been pursued by the OCP since its inception in 1974: (1) the identification and treatment of those with onchocerciasis; and ( 2 ) aerial larviciding of rivers to control the vector, Simulium damnosum. The core of vector control has been weekly larviciding with the chemical pesticides temephos, pyraclofos, permethrin, carbosulfan and the bacterial biological control agent, Bacillus thuringiensis var. isruelensas H 14 (BTI). Bacillus thuringiensis (BT) produces crystalline parasporal inclusions during sporulation which are pathogenic to insect larvae, and to dipteran larvae in particular for the var. israelensis strain (Goldberg and Margalit 1977 ; Thomas and Ellar 1983; Ellar et al. 1986; Anon. 1987; Hofte and