Natural abundance of the larval ectoparasitoid Diglyphus isaea walker was estimated on three summer host plants [tomatoes (Solanum lycopersicum), Bell peppers (Capsicum annuum), eggplants (Solanum melongena)] in Ojilate region. The parasitoid recorded low abundance in April on all studied host plants. Then developed high populations in May and June, the population then decreased by the end of the successive season. The parasitoid D. isaea showed 2-3 peaks of abundance on all investigated host plants, the highest one recorded 36, 29, and 16 individuals/ 50 infested leaflets on tomatoes, eggplant, and bell pepper respectively. The highest monthly average numbers in June on tomatoes recorded 26.25±3.86, in May on eggplants recorded 20.25±6.50, and in June on bell pepper recorded (20.25±6.50 individuals/ 50 infested leaflets). Moreover the highest average monthly percentages of parasitism occurred in May recorded (45.71±27.66, 41.04±25.13 and 25.19±11.19) on tomatoes, eggplants and bell pepper respectively

In this paper we define the Weyl algebra by two ways, and we study some theorems related to this algebra. We also study it widely as a ring of differential operators.