Simple SummaryAmbrosia beetles may constitute a serious problem in natural and agroecosystems. The use of entomopathogenic fungi has been proposed for their biocontrol. However, beetles’ cryptic behavior requires particular bioassays to determine the true impact of fungi on adults and their progeny. In this study, we evaluated the effect of exposing adult females ofXyleborus affinisand their progeny toBeauveria basssianain artificial diet bioassays. We demonstrated that the fungi biological activity onX. affinisadults and their progeny was limited to high doses of conidia suspension, since insect drilling behavior removes infective units.AbstractThe ambrosia beetleXyleborus affinis, recently reported affecting avocado trees in Mexico, represents one of the most widespread insects worldwide. Previous reports have shown thatXyleborusgenera members are susceptible toBeauveria bassianaand other entomopathogenic fungus strains. However, their effect on borer beetles’ progeny has not been fully investigated. The aim of the present study was to determine the insecticidal activity ofB. bassianaonX. affinisadult females and their progeny in an artificial sawdust diet bioassay model. TheB. bassianastrains CHE-CNRCB 44, 171, 431, and 485 were individually tested on females at concentrations ranging from 2 × 106to 1 × 109conidia mL−1. After 10 d of incubation, diet was evaluated to count laid eggs, larvae, and adults. Insect conidia loss after exposure was determined by attached conidia to each insect after 12 h of exposure. The results showed that females’ mortality ranged between 3.4% and 50.3% in a concentration–response manner. Furthermore, we did not observe statistical differences among strains at the highest concentration. CHE-CNRCB 44 showed the highest mortality at the lowest concentration and reduced larvae and laid eggs at the highest concentration (p< 0.01). Strains CHE-CNRCB 44, 431, and 485 significantly decreased larvae, as compared with the untreated control. After 12 h, up to 70% of conidia was removed by the effect of the artificial diet. In conclusion,B. bassianahas the potential to controlX. affinisadult females and progeny.