Abstract
Background The cotton aphid, Aphis gossypii Glov. (Hemiptera: Aphididae), is a major insect pest on a wide range of plants that causes high damage and transmits plant viruses. This study was carried out to evaluate an indigenous isolate, Beauveria bassiana (Bb), and extracts of 5 plant species: Psiadia penninervia, Pulicaria crispa, Euryops arabicus, Salvia officinalis, and Ochradenus baccatus against A. gossypii, as individual and combined treatments to estimate their compatibility under laboratory conditions. Also, the antifungal activity of these plant extracts against B. bassiana was evaluated. Results LC50 value was 8.64 x 10(4) spores/ml of Bb against A. gossypii, while LC50 values of the tested 5 plant extracts on A. gossypii were 103.64, 879.92, 747.90, 783.28, and 262.42 mu g/ml for P. penninervia, P. crispa, E. arabicus, S. officinalis, and O. baccatus, respectively. Both P. penninervia and O. baccatus extracts had the highest antifungal activities against Bb and were significantly different from the other 3 plant extracts. After 24 h of treatment with the combination of Bb and each extract, no effect for these combinations on A. gossypii mortality was recorded. Meanwhile, 5 days after treatment, the combined treatments between Bb and each plant extract achieved a significant increase in mortality than that of the single treatment with Bb or plant extract, except for P. penninervia extract, which did not achieve a significant mortality increase when combined with B. bassiana than that of its single treatment. Conclusion P. penninervia extract was not compatible with B. bassiana, but the other tested 4 plant extracts were compatible with B. bassiana. These 4 plant extracts could be used to control aphids in combinations with B. bassiana. Further laboratory and field investigations are needed to examine the effects of these plant extracts on other insect pests or associated beneficial insects.