Background: This study determined the nutrient requirements of Eldana saccharina Walker (Lepidoptera: Pyralidae), a serious sugarcane pest in South Africa, to develop a more efficient artificial diet for mass-rearing purposes for sterile moth production. Diets tested consisted of a minimum specification (MS) diet representing a diet formulated according to the minimum specification of a summary of published diets, which yielded satisfactory results; an ideal amino acid profile (IAAP) diet, where amino acid composition was based on the profile of amino acids in the 2nd (IAAP2) and 5th /6th (IAAP5/6) instar larvae; and lastly two diets based on the nutrient composition of the natural diet of the insects, papyrus (PAP) and sugarcane (SC). Six treatments with 50 replications were randomly allotted to 300 25 mL plastic screw-top vials. The diet (15 mL) was dispensed into each vial and inoculated with two freshly hatched larvae. Larvae, pupae, and moths were harvested at 28 days after inoculation. Overall survivability, pupal weight, sex ratio, and rate of development was determined and compared with the diet currently in use at the South African Sugarcane Research Institute (CON). Physical characteristics of the diets such as the pH and the water-holding capacity of the diets were also determined.
Results: The natural diets (PAP and SC) were not viable as they did not yield any results. Survivability was significantly higher (78%) for the MS diet whilst IAAP2 and IAAP5/6 yielded the second highest survivability (74%) compared to CON (68%). There were no differences in male pupal weights between all treatment diets, as was the case for female pupae. Within dietary treatments, female pupae were heavier than male pupae for all treatment diets. CON (1.0: 1.6) produced significantly less male than female pupae with MS (1.0: 1.2), IAAP2 (1.0: 1.0) and IAAP5/6 (1.0: 1.1) all producing equal amounts of male and female pupae. The MS diet (16%) yielded fourfold the number of moths after 28 days compared to CON (4%) and IAAP2 (4%) diets. IAAP5/6 yielded no moths after 28 days. The life stages thus developed fastest in the MS diet. The pH of all treatment diets remained stable for the entire duration of the trial. No biological contamination was observed through all diets. Differences in water-holding capacity were observed between most diets with PAP and SC losing the most moisture whilst the MS and IAAP2 diets retained the most moisture.
Conclusion: The MS diet most closely represented the nutrient requirements of E. saccharina, leading to its faster development on this formulation, which could be readily applied for large-scale production of this lepidopteran pest as an aid in the mass rearing of sterile males as part of the integrated pest management plan. © 2020 Society of Chemical Industry.
Keywords: integrated pest management; nutrient requirements; sterile insect techniques; sugar cane stalk borer.
© 2020 Society of Chemical Industry.