Effect of inoculation levels of 5-day old black soldier fly larvae (Hermetia illucens) on growth performance and substrate characteristics.

Abstract

Whereas Black Soldier Fly Larvae (BSFL) use the rearing substrate as feed, the substrate also doubles as its living environment. However this living environment is affected by substrate depth, larvae stocking densities, substrate moisture content, temperature and relative humidity. High stocking density negatively impacts weight gain of the larvae during their growth cycle due to increased waste accumulation and increased competition for feed amongst the larvae. The purpose of this study was therefore to determine an appropriate inoculation level of 5 Day Old Larvae (DOL) that gives optimal productivity performance of BSFL (Hermetia illucens) with brewers’ waste, wheat bran and shredded fruit waste mix as an organic substrate. The blended organic substrate was then inoculated with varying weights of 5-DOL as treatments. Each treatment consisted of 5.8, 4.8, 3.8, 2.8 and 1.8grams (g) of the larvae inoculated into 500 g of the substrate. The treatments were arranged in a 5 (inoculation level) × 3(days of data collection in the larval growth cycle) factorial arrangement, replicated 6 times in a Completely Randomized Design (CRD). The media and its inoculants was maintained at moisture content of 60%. Data was collected on morphometric growth parameters (length, girth and weight) and substrate characteristics (pH, colony forming units (cfu) and temperature) on days 0, 7 and 14. Although there was no significant difference (P˃0.05) in larval length at Day 0 and 7, on day 14 larval length varied (P<0.05) with 5-DOL inoculation level. Larval weight increased with decrease in 5-DOL inoculation level. Larval weight was highest (0.9 g) at inclusion level of 1.8 g and lowest (0.85 g) at inclusion levels of 5.8 and 3.8. The girth increased as the growth cycle progressed where the largest (0.70cm) was observed on day 14 while the smallest girth (0.20cm) was observed at day 0. Inoculation levels 5.8, 4.8 and 3.8 had similar girth means on the 14th day. However, the girth at inoculation level 1.8 g was different (P<0.05) from the inoculation intensities of 5.8 and 4.8 at same 14th day and it had the highest mean girth.Temperature values didn’t have a significant difference across all the treatments throughout the data collection period (P˃0.05). Bacterial population also showed a significant decline through the entire larval growth. The influence of both fungal and bacterial population on larval weight depended on the number of days at sampling. It was further revealed that there were interactions between fungal and bacterial population influenced by pH with its subsequent impact on weight gain. Inoculation levels of the 5-DOL interact with the number of days, age of larvae to influence weight and length of BSFL, microbial composition of the substrate and its pH.