Gall development and fine structure of the nutritive cells of Myopites blotii (Diptera, Tephritidae) on Inula salicina

Abstract

The tephritid fly Myopites blotii attacks the flower head of Inula salicina at the outset of anthesis. Their larvae tunnel through tubular florets, achenes, and vertically through the swollen, densely vascularized floral receptacle. The goal of the mining larvae is the large vascular bundles at the base of the bracts. The tunneling larvae cut a number of vascular bundles irrigating the florets and the resulting cavity is always open to the outside. Cell walls and cell remnants are continuously agglomerated by the larvae along the entrance channel, forming a black layer. Small patches of nutritive cells appear near severed vascular bundles that end in the larval cavity. The nutritive cells are activated to a high level of RNA and proteosynthesis. The cells have a dense cytoplasm and a large lobed nucleus with a large nucleolus. The long, flexuous plastids form a perinuclear crown. Numerous mitochondria and peroxisomes attest to intense respiration in these cells. The nutritive cells provide proteins and nucleoproteins to the larvae that also feed directly on the vascular bundles ending in the larval cavities. The more sedentary, nearly mature larvae concentrate their feeding activity toward the bottom of the larval cavity where a nutritive layer differentiates. A sclerenchyma layer forms that isolates the larval cavity from the vascular bundles of the floral receptacle. Key words: gall, nutritive tissue, floral receptacle, Tephritidae, Inuleae, Asteraceae.