*3.2. Bioassay*

Only the isolates of *B. bassiana*, *M. anisopliae and H. subulata* caused mortality against the larvae of *C. suppressalis*. A comparison of LC50 and LT50 values indicated the significant differences among the isolates. The most virulent, isolate BBLN1 (1 × 10<sup>4</sup> conidia/mL), had the least LC50 value, followed by BBAL1 (2.1 × 10<sup>4</sup> conidia/mL), BBRR1

(2.2 × 10<sup>4</sup> conidia/mL), BBLN2 (5.4 × 10<sup>4</sup> conidia/mL), BBAL3 (5.6 × 10<sup>4</sup> conidia/mL) and MASA (7.1 × 10<sup>4</sup> conidia/mL), while HSBL (1.6 × 10<sup>6</sup> conidia/mL), HSAL (7.9 × 10<sup>5</sup> conidia/mL) and BBLD5 (4.4 × 10<sup>5</sup> conidia/mL) showed the comparatively high LC50 values (Table 2). Moreover, the least LT50 values were obtained to be 2.71, 3.15, 3.45, 3.66 and 3.69 days for the larvae treated by BBRR1, BBLN1, BBAL1, BBAL4 and MASA, respectively (Table 3). These results revealed that BBRR1, BBLN1 and BBAL1 isolates of *B. bassiana* had higher efficacy than the other isolates on *C. suppressalis* larvae with a lesser concentration of conidia with a shorter time (days) to kill 50% of the larval population. Jandricic et al. [53] reported the higher virulence of *B. bassiana* isolates against the *Myzus persicae* Sulzer, *Aphis gossypii* Glover and *Aulacorthum solani* Kaltenbach (Hemiptera: Aphididae) compared to *M. anisopliae* isolates. Ramzi and Zibaee [12] showed that the two commercial isolates of *B. bassiana* and *B. bassiana* (BB1 and BB2) had the higher virulence against *C. suppressalis* larvae compared to *A. lecanii*, *I. fumosoroseus and M. anisopliae*. In addition, the higher virulence of the different isolates of *B. bassiana* and *M. anisopliae* has been observed on the boll weevil *Anthonomus grandis* Boheman (Coleoptera: Curculionidae) [29]. In our study, the least virulence of HSAL and HSBL as the two isolates of *H. subulata* were obtained compared to *B. bassiana* and *M. anisopliae* isolates, which may be correlated with low germination and sporulation rates in addition to the low activities of the extracellular enzymes of these isolates (see below) [54]. Finally, the isolates of *A. lecanii* and *A. muscarious* showed no mortality against *C. suppressalis* larvae. This case may be attributed to host–pathogen interaction between these isolates and the larvae of *C. suppressalis,* such as efficient attachment of conidia to the integument, negative impacts of integument composition with penetration tube of the fungi and immune responses of the larvae toward conidia. All these phenomena deserve detailed experiments to precisely elucidate the case.


**Table 2.** LC50 values (conidia/mL) of the entomopathogenic fungi collected from rice fields against the fourth instar larvae of *Chilo suppressalis*.

Note: calculations were carried out by POLO-Plus software.


**Table 3.** LT50 values (days) of the entomopathogenic fungi collected from rice fields against the fourth instar larvae of *Chilo suppressalis*.

Note: calculations were carried out by POLO-Plus software.
