An Edible-to-insects Calcium Alginate Gel as a Carrier for Entomopathogenic Nematodes

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Abstract
A carrier for entomopathogenic nematodes based on an edible-to-insects calcium alginate gel was developed. The alginate system was produced by external setting through an interaction between an aqueous sodium alginate mixture and calcium ions under acidic conditions. Sodium hexa-metaphosphate was used to control gel formation. Yeast extract used in the gel as a phagostimulant for Spodoptera littoralis larvae improved the insect's relative consumption rate and digestibility. The nematodes in the gel effectively controlled the larvae in a 24-h leaf bioassay, although nematode survival in the gel was ~ 50%. Gels subjected to 31% relative humidity (RH) prior to larval feeding became desiccated and were inedible to insects. However, gels at 61% RH supported larval feeding, although the water loss from the gel due to evaporation from 200-400-mg gel cubes at this humidity exceeded 50%. The gel might be a useful delivery system for nematodes against insects infesting the plant canopy in greenhouses.