Evaluation of different sponge types on the survival and infectivity of stored entomopathogenic nematodes

Abstract

Sponges are one of the cheapest and most suitable substrates used to formulate and/or store the infective juveniles (IJs) of entomopathogenic nematodes (EPNs). Our study investigated the survival and infectivity of the IJs on five different sponges compared to that in an aqueous suspension (control). The sponges were Oasis® floral, Nanosponge, Scotchbrite^TM, or Lysol® and natural sea sponge. EPN species tested were Heterorhabditis bacteriophora, Steinernema carpocapsae and S. feltiae. The recovery efficiency of the IJs from sponges was initially assessed. Subsequently, IJs were stored in the sponges and placed in plastic bags or Falcon tubes and incubated at 10° or 27 °C for 8 months or 11 weeks, respectively. IJ survival and infectivity were monitored monthly for the 10 °C and weekly for 27 °C in these sponge types. The IJs were recovered from the sponges, and their survival was based on observing their movement under a dissecting microscope, and infectivity was based on larval mortality in Galleria mellonella. Recovery efficiency of IJs was best for the Oasis floral sponge for all nematode species ranging between 83 and 91%. The survival and infectivity of stored IJs in all sponge types and control for both 10° and 27 °C gradually decreased over time. IJs stored in Scotchbrite, Lysol, and Nanosponge had the best survival and infectivity, whereas Oasis floral and natural sea sponges showed the poorest results. After 8 months at 10 °C in plastic bags, the survival ratio of all IJs in these three sponges (Scotchbrite, Lysol, and Nanosponge) was approximately 55%. IJs in Scotchbrite and Nanosponge were also able to survive and retain their infectivity at 27 °C for 3 months. IJs stored in Falcon tubes had survival that ranged from 26 to 53% at 27 °C and 55 to 77% at 10 °C. H. bacteriophora IJs lost their infectivity when stored at 27 °C after 10 weeks. However, S. carpocapsae and S. feltiae exhibited 85% infectivity when stored in Scotchbrite and 50% in Nanosponge, respectively. Overall, sponges made from polyurethane (Scotchbrite) followed by melamine (Nanosponge) and cellulose (Lysol) are recommended for long-term nematode storage and transportation of nematode samples. However, Oasis floral sponge may be preferred for short-term IJ formulation for field applications because of easier recovery of IJs.

Keywords: Biological control; Entomopathogenic nematodes; Formulation; Heterorhabditis; Steinernema; Storage.