Effects of an inorganic insecticide (boric acid) against Blattella germanicai: Morphometric measurements and biochemical composition of ovaries

Pestiferous cockroach species are closely associated with humans and are important for economic and public health points of view. In Algeria, Blattella germanica L. (Dictyoptera: Blattellidae) is a serious pest in the urban environment. Conventional insecticides, such as the organophosphates, carbamates, and pyrethroids, have been used widely to control cockroach which have developed resistance to these compounds. Thus, interest has been focused on lesser-used compounds. Boric acid was used as an insecticide for many years, especially against cockroaches. In order to obtain more information on the mode of action of boric acid, which has not been satisfactorily established, a biometric and biochemical study of the ovaries was done following the toxicity assays after having evaluated the toxicity of the boric acid against B. germanica. Boric acid was injected at two doses, 77.62 and 194.8 mu g/insect, corresponding to LC sub(50) and LC sub(90), respectively. The effect of this compound on reproduction was evaluated during the first gonatotrophic cycle (0, 2, 4 and 6 days) of the German cockroach, B. germanica. Different morphometric parameters on newly emerged female adults (number of oocytes, volume of basal oocytes, length and width of oocytes) were effectuated. The metabolite amounts, proteins and carbohydrates were determined. The results show that boric acid provokes an inhibition of the oogenesis, with a reduction of the oocyte number at day 2 only for the lower dose, and at days 2 and 4 for the higher dose. A reduction of the volume of basal oocytes was observed for all the tested doses. Vitellogenesis was clearly affected by this treatment. Biochemical analyses revealed a significant reduction of ovarian proteins and carbohydrates with the two tested doses.