Metarhizium brunneum (Ascomycota; Hypocreales) Treatments Targeting Olive Fly in the Soil for Sustainable Crop Production

Abstract

Soil treatments with Metarhizium brunneum EAMa 01/58-Su strain conducted in both Northern and Southern Spain reduced the olive fly (Bactrocera oleae) population density emerging from the soil during spring up to 70% in treated plots compared with controls. A model to determine the influence of rainfall on the conidial wash into different soil types was developed, with most of the conidia retained at the first 5 cm, regardless of soil type, with relative percentages of conidia recovered ranging between 56 and 95%. Furthermore, the possible effect of UV-B exposure time on the pathogenicity of this strain against B. oleae adults coming from surviving preimaginals and carrying conidia from the soil at adult emergence was also evaluated. The UV-B irradiance has no significant effect on M. brunneum EAMa 01/58-Su pathogenicity with B. oleae adult mortalities of 93, 90, 79, and 77% after 0, 2, 4, and 6 of UV-B irradiance exposure, respectively. In a next step for the use of these M. brunneum EAMa 01/58-Sun soil treatments within a B. oleae IPM strategy, its possible effect of on the B. oleae cosmopolitan parasitoid Psyttalia concolor, its compatibility with the herbicide oxyfluorfen 24% commonly used in olive orchards and the possible presence of the fungus in the olive oil resulting from olives previously placed in contact with the fungus were investigated. Only the highest conidial concentration (1 × 108 conidia ml−) caused significant P. concolor adult mortality (22%) with enduing mycosis in 13% of the cadavers. There were no fungal propagules in olive oil samples resulting from olives previously contaminated by EAMa 01/58-Su conidia. Finally, the strain was demonstrated to be compatible with herbicide since the soil application of the fungus reduced the B. oleae population density up to 50% even when it was mixed with the herbicide in the same tank. The fungal inoculum reached basal levels 4 months after treatments (1.6 × 103 conidia g soil−1). These results reveal both the efficacy and environmental and food safety of this B. oleae control method, protecting olive groves and improving olive oil quality without negative effects on the natural enemy P. concolor.

Compatibility between the endoparasitoid Hyposoter didymator and the entomopathogenic fungus Metarhizium brunneum: a laboratory simulation for the simultaneous use to control Spodoptera littoralis

“…On the other hand, we calculated the LC 50 of H. didymator inoculated with the EAMa 01/58‐Su strain, which was of 1.85 × 10 6 conidia ml −1 . Although our results are consistent with those obtained for this strain and other parasitoids, it is shown that the susceptibility of H. didymator to EAMa 01/58‐Su is higher than those evidenced by different insect pests . This result is of great importance to develop a suitable strategy for biological control as it allows to compare the susceptibility of the parasitoid with other insects.…”

“…(Hymenoptera: Braconidae), were susceptible to B. bassiana and M. anisopliae . Similarly, our previous work with the same strain (EAMa 01/58‐Su) and the same concentration (10 8 conidia ml −1 ) that we used in the present article, showed that the fungus caused a mortality of 21% on adults of the cosmopolitan parasitoid Psyttalia concolor Szepliget (Hymenoptera: Braconidae) …”

“…Similar results were obtained by Yousef et al . when using the EAMa 01/58‐Su strain against P. concolor , with fungal outgrowth values depending on the experimental methods …”

“…Four concentrations of conidia in suspension were prepared in a sterile solution of 0.1% Tween 80 (10, 10, 10 7 and 10 8 conidia ml −1 ); the control was 0.1% Tween 80 without conidia. These concentrations were selected based on our previous studies . Newly‐emerged adult parasitoids were cold‐anesthetized and sprayed, in replicate groups of 10, with conidial suspensions (or 0.1% Tween 80 [control]) in a Potter tower (Burkard Manufacturing Co. Ltd, Rickmansworth, United Kingdom), which deposited 1.54 ± 0.06 mg cm −2 at 0.7 bars of pressure.…”

“…Indeed, our previous studies have reported the efficacy of several isolates of entomopathogenic fungi for control of S. littoralis , both by direct inoculation of larvae with the fungus and by feeding larvae with leaves from endophytically‐colonized plants . The M. brunneum isolate EAMa 01/58‐Su, in particular, has been shown to be virulent against S. littoralis and other economically important insect pests …”