Abstract
The entomopathogenic fungus L. lecanii has been developed as biopesticides and used widely for biological control of several insects in agricultural practice. Due to the lack of isolation/count methods for L. lecanii in soil, the persistence of this fungus in soil appears to have attracted no attention. A selective medium and count method for L. lecanii in soil based on cetyl trimethyl ammonium bromide (CTAB) was developed, and then the persistence and viability of this fungus in soil were investigated under field conditions between 2012 and 2014. The results showed that the rate of recovery for L. lecanii in soil on the selective CTAB medium was satisfactory. The minimum CFUs for L. lecanii on the selective medium (0.5 g/L CTAB) was about 102 conidia/g soil. The L. lecanii density in soil declined quickly in the first month after inoculation with fungal conidia, kept stable for 6 to 10 months, and then decreased gradually until undetectable. L. lecanii could persist for at least 14 months in the agricultural soil of northern China. The colony growth, conidia yield and germination rate on plates, as well as the median lethal concentration or times (LC50 or LT50) to aphids, mycelium growth in aphids and sporulation on aphids of L. lecanii did not change significantly during the persistence in soil. In general, the count method developed here was a very useful tool for monitoring the dynamics of natural or introduced L. lecanii populations in soil, and the data on the persistence of L. lecanii in soil reported here were helpful for biological control and environmental risk assessment.
Highlights
Entomopathogenic fungi (EPF) play a crucial role in the control of pest insect populations in nature [1,2], and have been considered as an important supplement or attractive alternative to chemical insecticides [3,4]
The colony forming units (CFU) values of M. anisopliae on Oatmeal agar (OA)-D were significant with regard to the other treatments and the rate of recovery on OA-cetyl trimethyl ammonium bromide (CTAB) ranged from 48.5%57.4%
A. niger, F. oxysporum and P. digitatum did not grow on OA-D or any OA-CTAB media, whereas A. alternate and V. dahlia were detectable on OA-CTAB4 with the rate of 9.9% and 30.1% respectively
Summary
Entomopathogenic fungi (EPF) play a crucial role in the control of pest insect populations in nature [1,2], and have been considered as an important supplement or attractive alternative to chemical insecticides [3,4]. Several species of EPF have been formulated, registered and used as mycoinsecticides in the world [5]. The mycoinsecticides often do not match the efficacy of cheaper chemical pesticides in the field application, which is the primary obstacle to their commercialization and large-scale application [6,7,8]. The inconsistent performance of biological control agents is often associated with an incomplete understanding of the ecological.
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