Biological control of citrus rust mite Phyllocoptruta oleivora by three bacterial species

The citrus rust mite, Phyllocoptruta oleivora (Acari: Eriophyidae) is a major pest of citrus in most humid regions of the world due to the cost of control and damage caused to fruits. The adverse effects on non-target organisms, the environment and increasing resistance associated with chemical acaricides have increased the need for biological control alternatives. The purpose of this study was to evaluate the effect of three bacterial species Streptomyces thinghirensis strain HM3, Streptomyces tricolor strain HM10 and Bacillus subtilis E5 on mortality rate of P. oleivora under laboratory and field conditions. Additionally, we investigated their adverse consequences on the predatory mite, Amblyseius swirskii Athias-Henriot (Acari: Phytoseiidae). The greatest efficiency rate on P. oleivora was noted with S. thinghirensis strain HM3 sprays. Four days after treatment, mite mortality was 89.26 and 84.47% under lab and field conditions, respectively, followed by S. tricolor strain HM10, which showed miticidal activity against mobile stages of P. oleivora. Six days after treatment, mite mortality reached 84.90 and 83.66% under lab and field conditions, respectively. Furthermore, the death rates were noticeably lower (72.60% and 71.25%) using B. subtilis E5 under lab and field conditions, one week after treatment. The predatory mite, A. swirskii, displayed higher capacity for tolerance than P. oleivora to the three bacterial species. The corrected mortality percentages were 17.21, 15.30 and 13.10% under lab conditions and 15.89, 13.41 and 11.76% under field conditions after one week of exposure with S. thinghirensis HM3, S. tricolor HM10 and B. subtilis E5 respectively. S. thinghirensis and S. tricolor exhibited ovicidal activity against laid eggs of P. oleivora under laboratory conditions. Where suppressed hatching of 65.52, 63.26% of laid eggs of P. oleivora, respectively. While B. subtilis E had no impact on the eggs. Exploring the genome of S. thinghirensis HM3 revealed a potential biosynthetic gene cluster (BGC) related to the antibiotic actinomycin D production. This pathway contained more than 29 gene classified as regulators, transporters and functioning genes. Besides, possible 7 and 8 proteases and protease inhibitors were identified inside the genome of HM3 and HM10, respectively. This study presents a potential novel approach for biocontrol of citrus rust mite, P. oleivora, highlighting their applicability in P. oleivora population management.