Ultrastructure and optical features of compound eyes in Odontothrips loti (Thysanoptera: Thripidae).

Thrips (Thysanoptera) are minute insects of ecological and economic importance, yet their visual systems remain poorly documented. Here, we present a comprehensive morphological and optical analysis of the compound eyes of Odontothrips loti, an important alfalfa pest, using scanning and transmission electron microscopy. The compound eyes of adult O. loti conform to the apposition type and contain 56-63 ommatidia per eye. Sexual dimorphism is evident, with females exhibiting larger facets than males. Each ommatidium comprises a cornea, a eucone-type crystalline cone, seven retinula cells, two primary pigment cells, and an undetermined number of secondary pigment cells. Quantitative measurements show relatively wide interommatidial (Δφ) and rhabdom acceptance angles (Δρrh), low F-numbers (F), and elevated eye parameter (P) values, which are optical characteristics frequently associated with strong size constraints in miniature insects. These findings reveal a compact visual system shaped by the morphological limitations imposed by miniaturization and contribute to a broader understanding of visual diversity in Thysanoptera.