An Improved Bioassay Method for Entomopathogenic Fungi of Sugarcane Pests and Its Evaluation in Studies of Virulence in Subcultures

Abstract

An improved bioassay method was developed for evaluating entomopathogenic fungi (EPF) using pests and fungi from sugarcane crop system. Third instar larvae of white grub Holotrichia serrata F. (Coleoptera: Scarabaeidae) and shoot borer Chilo infuscatellus Snellen (Lepidoptera: Crambidae) surface-contaminated with suspensions (10 8 spores/ml) of Beauveria brongniartii (Sacc.) Petch and Beauveria bassiana (Balsamo-Criv.) Vuill., respectively were subjected to starvation and feeding regimes. Holotrichia serrata grubs maintained in starvation regime showed lower overall mortality and higher LT 50 values than those kept in feeding regime in one test; the trend was, however, opposite in the second test. On the other hand, C. infuscatellus larvae in starvation regime produced higher mortality and lower LT 50 values than those in feeding regime in both tests. Further, spore output per C. infuscatellus larval cadaver was equal in both regimes. In degeneration studies, spore output of Metarhizium anisopliae Metch. maintained on nutrient broth for 15 continuous subcultures showed overlapping differences and a decreasing trend after the first six subcultures. In virulence studies with M. anisopliae from eight subcultures against diet-reared C. infuscatellus, third instar larvae treated with the fungus and maintained under starvation regime showed two peaks of LC 50 and LT 50 values. In comparative studies with field-collected C. infuscatellus, third instar larvae treated with 10 8 spores/ml of the fungus from 15 subcultures and fed with sugarcane shoots showed indistinct peaks in per cent mortality which reached significantly lowest value in the 15th subculture. The advantages of the modified bioassay method in virulence tests and the importance of degeneration studies for candidate EPF such as B. brongniartii are discussed.

Metarhizium majus and Metarhizium robertsii show enhanced activity against the coleopteran pests Holotricha serrata and Oryctes rhinoceros

“…Thamari Chelvi et al (2011) M. anisopliae against H. serrata and obtained a mean mortality of 81% with liquid formulation containing 1x10 8 conidia/ml and 76-78% mortality was obtained with powder formulations containing 4x10 8 spores/g in 15 days. Srikanth et al (2011) also used conidial suspension @ and obtained LC 50 of 9.28x10 7 conidia/ ml in 7 days. Powder formulations of M. anisopliae species were used against lepidopteran or coleopteran larvae primarily employed the method of surface contamination with conidial suspension followed by provisioning of food such as roots or shoots in containers (Easwaramoorthy et al 2004;Srikanth et al 2006;Manisegaran et al, 2011) and application of M. anisopliae @ 4×10 9 conida/ml gaveg 92% control of white grub population at 30 days.…”

“…There are several studies conducted to prove the efficacy of Metarhizium against many insect pests, they are mostly based on M. anisopliae. Against Holotrichia serrata strains of M. anisopliae have been shown to cause infection and formulations have been used in sugarcane fields to bring down the white grub population (Srikanth et al, 2011;Shanmugam et al, 2014;Sathayaraj and Karthick 2008;Thamarai Chelvi et al, 2011;Pradya and Mohit, 2014). M. anisopliae have been tested for control scarab species of several coleopteran beetles (Hurpin and Robert, 1972).…”

A 100 years of biological control of sugarcane pests in India: review and perspective.

“…Compatibility of pesticides with three species of EPF was examined and strategies for the integration of the two tools were suggested [341]. An improved bioassay method for evaluating EPF of sugarcane pests by maintaining treated larvae under starvation was standardized, and the method was further evaluated in studies of EPF virulence in subcultures [342].…”

Virulence of Beauveria brongniartii and B. bassiana against Schizonycha affinis white grubs and adults (Coleoptera: Scarabaeidae)

“…; Srikanth et al. ). The discovery of fungal epizootics on H. sommeri and S. affinis provided evidence that natural enemies were available to periodically regulate these pest populations.…”

“…This work followed observations made by Hatting (2008) on an epizootic caused by an unknown Beauveria species on H. sommeri in the same region. Beauveria brongniartii is one of the most important, virulent and widely distributed pathogens of the Melolonthinae (Rombach et al 1994;Townsend et al 1995;Cravanzola et al 1997;Piatti et al 1998;Vestergaard et al 2002;Keller et al 2003;Easwaramoorthy et al 2004;Srikanth et al 2011). The discovery of fungal epizootics on H. sommeri and S. affinis provided evidence that natural enemies were available to periodically regulate these pest populations.…”