A laboratory study on survival and infectivity of entomopathogenic nematodes formulated in gum katira-based biogel compositions

Insufficient analysis of carriers and their interaction with biocontrol agents can lead to ineffective formulations. Therefore, it is important to thoroughly study the compatibility and interactions between carriers and biocontrol agents for high-quality biological formulations. The present study aimed to evaluate the effect of four different formulation compositions containing gum katira biogel, vermiculite, and diatomaceous earth on the survival and infectivity of infective juveniles (IJs) of two entomopathogenic nematodes (EPNs) species namely, Steinernema abbasi and Heterorhabditis indica at 25 and 35 °C. The physicochemical analysis of the prepared formulations revealed their slightly acidic nature with pH ranging from 5.65 to 6.10. Rheological studies validated the solid-like behavior of the developed formulations. The highest survival of S. abbasi IJs was observed in the case of gum katira biogel-vermiculite blended composition at both 25 °C (94.2%) and 35 °C (88.4%) after 90 days of storage. Interestingly, gum katira biogel alone sustained maximum survival percentage (63.5%) of H. indica as compared to control (41.5%) after 90 days at 25 °C. The formulation compositions failed to retain alive H. indica IJs at 35 °C even after seven days of storage. Moreover, the gum katira singly or in combination with vermiculite resulted in superior infectivity against Galleria mellonella (4th instar larvae) as compared to the other treatments in case of both the nematode species. The presence of diatomaceous earth in all the compositions irrespective of moisture and EPN species showed a negative impact on the survival and infectivity of IJs after 90 days of storage. Gum katira biogel alone or in combination with vermiculite was favorable to sustaining the survivability and infectivity of test EPN IJs at ambient storage temperatures. These formulants can further be used to develop biocontrol EPN formulations for organic farming and integrated pest management programs.