The conidial tolerance of Metarhizium anisopliae var.anisopliae isolate ARSEF 2575 to UV-B irradiation is greatly influenced by growth-environment alterations.In this review,we report high variability in conidial UV-B tolerance in response to altered culture conditions.Conidia produced on insect cadavers[Zophobas morio(Coleoptera)or Galleria mellonella(Lepidoptera)] had low tolerance to UV-B radiation;and conidia produced on potato dextrose agar supplemented with yeast extract(PDAY)had medium UV-B tolerance;whereas conidia produced on a minimal medium without any carbon source(MM),on MM with a non-preferred carbon source such as lactose(=MML),on PDAY plus 1 M NaCl or KCl,or PDBY with high alkalinity had the highest UV-B tolerances.All of the above conditions that induced high UV-B tolerance,however,also greatly reduced conidial production.Comparisons between stress tolerance and conidial production,particularly with conidia produced under osmotic and nutritive stress,point out that the benefits of producing very tolerant conidia have the enormous cost of low conidial production.Growth under visible light also greatly improved conidial UV-B tolerance,but light did not negatively influence conidial production.Therefore,culture on rich media under light is proposed as the most promising approach to producing conidia with improved UV-B tolerance for biological control of pest insects in agriculture. The conidial tolerance of Metarhizium anisopliae var. Anisopliae isolate ARSEF 2575 to UV-B irradiation is greatly influenced by growth-environment alterations. In this review, we report high variability in conidial UV-B tolerance in response to altered culture conditions. Conidia produced on insect cadavers [Zophobas morio (Coleoptera) or Galleria mellonella (Lepidoptera)] had low tolerance to UV-B radiation; and conidia produced on potato dextrose agar supplemented with yeast extract (PDAY) had medium UV-B tolerance; minimal medium without any carbon source (MM), on MM with a non-preferred carbon source such as lactose (= MML), on PDAY plus 1 M NaCl or KCl, or PDBY with high alkalinity had the highest UV-B tolerances.All of the above conditions that induced high UV-B tolerance, however, also greatly reduced conidial production. Comparisons between stress tolerance and conidial production, particularly with conidia produced under osmotic and nutritive stress, point out that the benefits of producing very tolerant conidia have the huge cost of low conidial production. Growth under visible light also greatly improved conidial UV-B tolerance, but light did not negatively influence conidial production. Beforefore, culture on rich media under light is proposed as the most promising approach to producing conidia with improved UV-B tolerance for biological control of pest insects in agriculture.