Screening of tropical isolates of Metarhizium anisopliae (Hypocreales: Clavicipitaceae) for virulence to the sweet potato weevil, Cylas formicarius (Coleoptera: Brentidae)

Abstract

The sweet potato weevil (SPW), Cylas formicarius, is a serious pest of sweet potato in Australia and Papua New Guinea. Ten strains of Metarhizium sp. isolated from Australian soil samples were evaluated for their growth characteristics and screened for virulence to adult SPW under laboratory conditions. All isolates except QD62 (48.6%) had moderate to high germination (66 -97%), and all took 2 to 4 days to sporulate at 25 8C. The optimal temperature for radial growth for the majority of isolates was 30 8C, and there was a significant interaction between isolate and temperature (P , 0.05). Isolate QS155 showed the fastest radial growth at 30 8C. The internal transcribed spacer sequences showed slight variations among the isolates; however, all isolates were shown to be Metarhizium anisopliae. Isolates varied greatly in their virulence. At 10 days after inoculation (DAI) by immersion in a suspension of 1 £ 10 7 conidia/ml, 9 of the 10 isolates were virulent, causing 80-100% mortality of adult SPW. Only two isolates (QS001-6 and QS155) caused more than 50% mortality at 5 DAI. In dose-mortality bioassays, isolate QS155 had the lowest 20-day LC 50 and LC 90 values; however, there were no statistically significant differences in mortality among the three most promising isolates tested (QD66, QS001-6 and QS155). These results show that M. anisopliae isolate QS155 has potential as a microbial control agent for SPW, and that further evaluation under glasshouse and field conditions is warranted.

Phenotypic, molecular, and virulence characterization of entomopathogenic fungi, Beauveria bassiana (Balsam) Vuillemin, and Metarhizium anisopliae (Metschn.) Sorokin from soil samples of Ethiopia for the development of mycoinsecticide

“…Generally, the present study recognized superior germination percentage (99.67%) rated by isolate AAUKB-11 whereas the radial growth rate (3.43 mm day À1 ) and sporulation (4.60 Â 10 8 sporse/ml) attained with isolate AAUMFB-77. In entomopathogenic fungi, fast conidia germination, radial growth (Dotaona et al, 2015), and high sporulation rates (Mar et al, 2012) are pathogenicity determinates that positively correlated with fungal virulence. Therefore, screening of entomopathogenic fungi by germination, radial growth, and sporulation parameters could be paramount important to determining high virulent isolates.…”

Niche adaptations and plasticity within the fungal entomopathogenic genus >i<Metarhizium>/i< in Brazil

“…used against different hosts (e.g. Brunner-Mendoza et al, 2017;Dotaona et al, 2015;Oreste et al, 2012;Resquín-Romero et al, 2020), and in our study, such variation was also detected when fungal treatments were applied through the spray tower, and for the bait technique. Ondiaka et al (2008) reported intraspecies variability for M. anisopliae and Beauveria bassiana tested against adults of the sweet potato weevil Cylas puncticollis (concentration: 10 7 conidia mL -1 ), and stated that strain selection is needed for biological control.…”

Virulence Screen of Beauveria Bassiana Isolates for Australian Carpophilus (Coleoptera: Nitidulidae) Beetle Biocontrol

“…Standard inoculation procedures were employed for both the adult and larval assays to ensure that consistent spore loads were delivered to each insect and results were thus comparable to other EPF bioassays. The immersion treatment protocol used on adult Carpophilus beetles in this study gave rise to an average mortality rate that was considerably lower compared to similar EPF assays conducted on other adult Coleoptera: for example nine isolates of Metarhizium anisopliae on sweet potato weevil using the same inoculation method, carrier, time and dose-rate, had 100% mortality after 10 days in six of the nine isolates [28]. Similarly, mortality rates between 97.5%-100% for emerald ash borer adults treated with three B. bassiana and two M. anisopliae isolates under the same application regime, incubated for six days [29].…”