Effect ofAmblyseiuscucumeris andAmblyseius barkerias biological control agents ofthrips tabacion glasshouse cucumbers

Abstract
Biological control of Thrips tabaci by the phytoseiid mites Amblyseius cucumeris and Amblyseius barkeri was investigated on glasshouse parthenocarpic cucumbers. The mite species were used in combination and singly. Successful thrips control was obtained with A. cucumeris alone, whereas control was not reliable with A. barkeri alone nor with the combination of A. cucumeris and A. barkeri. The establishment period was long for both phytoseiid species. At the beginning of the trial, when thrips were absent or very low in numbers, only A. cucumeris was found on the leaves. Mite populations did not increase until the number of thrips were ca. two and five per leaf for A. cucumeris and A. barkeri, respectively. A. cucumeris seemed to show a better numerical response to T. tabaci than A. barkeri. At the end of the trial (three months after the last introduction of mites) only A. barkeri was found in the combination plot, indicating that A. cucumeris is displaced by A. barkeri in situations of interspecific competition between the two species on glasshouse parthenocarpic cucumbers.