Canola bee pollen is an effective artificial diet additive for improving larval development of predatory coccinellids: a lesson from Harmonia axyridis.

Abstract

Pollen is a common plant-derived food source for predatory ladybird beetles under field conditions, while the potential for pollen to improve the quality of artificial diets remains largely unexplored. In this study, we developed three pollen diets by incorporating varying proportions of canola bee pollen (7.5%, 15.0%, and 22.5% with proportioned water) into a conventional diet. The feeding efficiency of Harmonia axyridis, an omnivorous predator, was evaluated and compared on three pollen diets, a conventional non-pollen diet and pea aphids. The larvae fed a medium or high pollen diet exhibited significantly higher survival in the fourth instar, pupa and adult stages than those fed a non-pollen diet. These larvae also developed into significantly heavier adults, and their survival rates in adulthood were comparable to those fed pea aphids. Specifically, we revealed the underlying mechanisms through which a high pollen diet enhances pupal development. Consumption of high pollen diet versus non-pollen diet resulted in a significant decrease in pupal glycogen content but an increase in adult lipid content. Both diet treatments induced similar changes in carbohydrate and glycogen content compared to the aphid diet while exhibiting different alterations in pupal protein content and adult lipid content. Furthermore, the transcriptome analysis revealed that the nutrient metabolism, immune response, and cuticle development pathways were predominantly enriched among the differentially expressed genes (DEGs). Canola bee pollen offers diverse advantages in terms of rearing H. axyridis larvae with an artificial diet, which will advance the development of effective diets for predaceous coccinellids. This article is protected by copyright. All rights reserved.