Sex-specific perching: Monitoring of artificial plants reveals dynamic female-biased perching behavior in the black soldier fly, Hermetia illucens (Diptera: Stratiomyidae)

Abstract

Artificial perches are implemented by many companies that mass-rear the black soldier fly, Hermetia illucens, to create a more natural breeding environment or provide additional surface area for flies to rest. However, basic information related to perching behavior is lacking. This experiment tested the effect of adding perches to breeding cages on fitness and behavior. Perches were constructed from artificial leaves affixed to wooden dowels inserted into foam blocks, placed in the center of cage floors. The four treatment-levels had an added surface area of 0.00-, 0.04-, 0.26-, and 0.34-m2. Each 0.93-m3 cage was supplied with 90 male and 90 female flies, and female thoraxes marked with acrylic paint. Beyond the tested range, a linear model suggests that 1.00-m2 additional surface area can accommodate a 1.46-fold increase in flies without negative fitness impacts. Time-series analysis revealed; (a) females utilized perches 1.42-times more often than males across two trials; (b) especially in the morning where the difference could be as high as 2.56-times more than males; (c) this decreased to 0.20-1.57 times more females than males by 1600 h, and (d) this cyclical pattern repeated each day throughout the week with decreasing female-bias, starting from 2.41-times more females on Day 1 to 0.88-1.98-times more females than males on Day 6. These dynamics are likely due to the presence of male flies engaging in aerial contests near lamps providing light needed for mating, especially during early hours and early adulthood, aligning with prior knowledge of black soldier fly mating behavior.