Impact of flower rewards on phytophagous insects: importance of pollen and nectar for the development of the pollen beetle (Brassicogethes aeneus)

Entomophilous plants reward pollinators with provision of nutrient-rich foods such as pollen and nectar. These rewards contain compounds that are essential to insect development and can be used by pollinators as well as herbivorous insects. The pollen beetle ( Brassicogethes aeneus , syn. Meligethes aeneus ) whose larvae develop in oilseed rape flowers ( Brassica napus ) is known to feed on pollen. Previous studies already showed the importance of pollen on the development of this insect but it seems that other resource, such as nectar, could also be used. The purpose of this study was to assess the respective roles of pollen and nectar on pollen beetle development. We tested their role with behavioural and developmental experiments using flowers where the presence and absence of nectar and pollen varied. Larvae, irrespective of their instar, fed both on anthers and nectar. Nectar did not influence larval development or adult survival while pollen influenced development by increasing both larval and adult weight. However, pollen did not affect larval or adult survival nor development time. These results indicate that pollen beetle larvae are adapted to deal with various diets and can complete their development without pollen or nectar.