Phytosanitary irradiation (PI) has been successfully used to disinfest fresh commodities and facilitate international agricultural trade. Critical aspects that may reduce PI efficacy must be considered to ensure the consistency and effectiveness of approved treatment schedules. One factor that can potentially reduce PI efficacy is irradiation under low oxygen conditions. This factor is particularly important because storage and packaging of horticultural commodities under low oxygen levels constitute practices widely used to preserve their quality and extend their shelf life. Hence, international organizations and regulatory agencies have considered the uncertainties regarding the efficacy of PI doses for insects infesting fresh commodities stored under low oxygen levels as a rationale for restricting PI application under modified atmosphere. Our research examines the extent to which low oxygen treatments can reduce the efficacy of phytosanitary irradiation for tephritids naturally infesting fruits. The effects of normoxia (21% O2), hypoxia (~5% O2), and severe hypoxia (< 0.5% O2) on radiation sensitivity of third instars of Anastrepha fraterculus (sensu lato), A. ludens (Loew), Bactrocera dorsalis (Hendel), and Ceratitis capitata (Wiedemann) were evaluated and compared at several gamma radiation doses. Our findings suggest that, compared to normoxia, hypoxic and severe-hypoxic conditioning before and during irradiation can increase adult emergence and contribute to advancement of larval development of tephritid fruit flies only at low radiation doses that are not used as phytosanitary treatments. With phytosanitary irradiation doses approved internationally for several tephritids, low oxygen treatments applied before and during irradiation did not increase the emergence rates of any fruit fly species evaluated, and all treated insects died as coarctate larvae. Thus, the findings of our research support a re-evaluation of restrictions related to phytosanitary irradiation application under modified atmospheres targeting tephritid fruit flies.

The interaction between the entomopathogenic fungus Beauveria bassiana (Balsamo) and the parasitoid Coptera haywardi (Oglobin), as potential biological control agents for Anastrepha obliqua (Macquart) fruit flies, was evaluated under laboratory and semi-protected field cage conditions. The effects of the parasitoids and fungus were individually and jointly assessed in Plexiglas cages. Application of B. bassiana dry conidia to soil produced 40% mortality in A. obliqua adults. However, mortality was lower (21.2%) on evaluation under field cage conditions. According to the multiple decrement life table analysis, the probability of death of A. obliqua was 88% when C. haywardi parasitoids and B. bassiana conidia were used in conjunction, 89% when only C. haywardi parasitoids were released and 23% when only B. bassiana conidia were applied. These results demonstrate that no synergistic, additive or antagonistic interaction took place with the simultaneous use of these natural enemies, since the presence of B. bassiana had no effect on the C. haywardi parasitism. These results indicate that the parasitoid is a better natural enemy for the control of A. obliqua, and show that, although the two biological control agents can be used simultaneously, their joint application will not produce increased control.

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The capacity of a parasitoid to discriminate hosts can favor the survival of its progeny as well as improve its efficacy as a biocontrol agent when it is used with another natural enemy, as this may result in greater control of the pest. Our aim was to characterize the discrimination ability of Coptera haywardi (Oglobin) (Hymenoptera: Diapriidae) females with respect to puparia of Anastrepha obliqua (Macquart) (Diptera: Tephritidae) treated with the fungus Beauveria bassiana (Balsamo) Vuillemin (Hypocreales: Cordycipitaceae), under three conditions: (1) no choice, separately exposing A. obliqua puparia, treated at 0, 24, 48, or 72 h prior to exposure, to the parasitoid and without application of the fungus (absolute control); (2) with the possibility of choosing between untreated and treated puparia with the same times after fungus application; and (3) multiple choice, where parasitoids could select among puparia treated at different times. Observations were made to determine the discrimination behavior of the wasps as well as the number of ovipositions by each female parasitoid; 14 observations were made. Coptera haywardi exhibited different levels of discrimination depending on the test. In the no‐choice test, discrimination was not observed; in the two‐choice test, females significantly discriminated the puparia treated at 0, 24, and 72 h prior to exposure; and in the multiple‐choice test, females preferred the untreated puparia – behavior that was corroborated in the direct observations. Oviposition time ranged from 9 to 86 min and differences in average time among treatments were not significant. We conclude that the discrimination ability of C. haywardi allows the simultaneous use of B. bassiana, as females prefer healthy, untreated puparia without interfering with the fungus.