Two-fold application of Bacillus cereus followed by Heterorhabditis indica to manage Holotrichia consanguinea adversely effects nematode reproduction.

Holotrichia consanguinea is a destructive pest of sugarcane in India. Out of urgent need to control the grubs, indiscriminate application of Bacillus cereus followed by Heterorhabditis indica is practiced. Based on the compatibility studies between the two bioagents, we found that B. cereus-treated grubs succumbed faster to H. indica infection suggesting synergism. Infection with H. indica even at the minimum dose of 250 IJ/grub decreased the survival to 3.7 ± 1.33 days, compared to 9.2 ± 1.93 days in untreated grubs. The Kaplan-Meier estimates depicted reduced survival time gap between treated and untreated grubs for all probability levels with an increase in nematode dose. Following mortality, the cadavers supported 65.2 % higher multiplication of Photorhabdus luminescens over B. cereus till day three, which gradually reversed to 67.5 % in favour of B. cereus by day eight. The suppression of P. luminescens by B. cereus had negative implication on the growth and development of H. indica as it coincided with significant decline in the production of hermaphrodites, females and the final recovery of the infective juveniles after 3, 6 and 8 days of insect death, respectively. Recommending combined application of the two bioagents can have a negative implication on the long-term persistence of H. indica.