Assessment of aphid lethal paralysis virus as an apparent population growth-limiting factor in grain aphids in the presence of other natural enemies

afrique du sud braconidae campo champ coccinellidae coleoptera depredadores diptera fields hippodamia hippodamia variegata hymenoptera insect pests insecte nuisible insecte utile parasitoides parasitoids pest insects pests of plants plagas de plantas plant pests predators predatory insects ravageur des plantes rhopalosiphum padi scathophagidae sitobion avenae south africa syrphidae triticum aestivum useful insects