Laboratory and field studies on the infection of stink bugs, nezara viridula, piezodorus guildinii, and euschistus heros (Hemiptera: pentatomidae) with metarhizium anisopliae and beauveria bassiana in brazil
Isolates of Metarhizium anisopliae (CNPSo-Ma12) and Beauveria bassiana (CNPSo-Bb56) were tested under field conditions as biological control agents of soybean stink bugs (Nezara viridula, Piezodorus guildinii, and Euschistus heros). Kaolin-based powder formulations of M. anisopliae or B. bassiana were applied to soybean plots at a rate of 1.5 x 10(13) conidia per ha. After treatment, field cages (0.25 m2) were placed in plots and stink bug adults were introduced into the cages. Mycosis for both P. guildinii and N. viridula was initially observed 7 days postapplication in the 1991 season and at 15 days postapplication in the 1992 season. For E. heros, mortality was detected on day 8 and on day 20 in 1991 and 1992, respectively. In 1991, infection levels of 48 and 41% were achieved at day 30 for P. guildinii and N. viridula, respectively, whereas the infection level in E. heros reached only 33%. In 1992, mortality caused by M. anisopliae on the three stink bug species was lower than that observed in 1991, with cumulative mycosis at day 30 being 15, 17, and 20% for P. guildinii, N. viridula, and E. heros, respectively. The 1991 season was humid and warm, whereas in the 1992 season there was an 8-day drought spell (<75% relative humidity (RH)) after application, suggesting that %RH was responsible for an earlier occurrence and a higher prevalence of both fungi on stink bug species in the 1991 trial. Despite the higher deposition of B. bassiana on the plants (17 colony forming units [CFU] per mm2 of leaflet) 1 day after application compared to M. anisopliae (5.1 CFU per mm2 of leaflet), B. bassiana was less efficient against stink bugs than M. anisopliae. Field results were confirmed through laboratory bioassays, in controlled conditions (T = 26 +/- 1.5 degreesC, 90% RH, and 8D:16L light regimen). The mean time to mortality by M. anisopliae was 4.3 +/- 0.2 days for P. guildinii, 4. 6 +/- 0.2 days for N. viridula, and 7.4 +/- 0.5 days for E. heros. E. heros was less susceptible and P. guildinii was the most susceptible species to M. anisopliae. Since these species usually occur as a complex in soybean in Brazil, these results represent important information toward the development of entomopathogenic fungi as microbial insecticides of these pests. Copyright 1998 Academic Press.
Sosa-Gmez
DR
Embrapa-National Soybean Research Center, Londrina, PR, 86001-970, Brazil.
Moscardi
F