The Oviposition Site Selection and Photoperiod Regulation of Megalurothrips usitatus (Thysanoptera: Thripidae) in Different Cowpea Plant Parts.

Megalurothrips usitatus (Thysanoptera: Thripidae) is a key destructive pest of cowpea, resulting in considerable economic losses. Understanding M. usitatus's oviposition preference in various plant parts under distinct photoperiod treatments is important for its success in pest control. We placed mated females with cowpea stems, leaves and pods in rearing boxes. After 24 h, eggs were counted after basic fuchsin staining. Hatched nymphs were recorded over 7 days. Morphology and histology were examined by microscopy and scanning electron microscopy. A statistical comparison on the number of egg-laying and hatching nymphs was conducted in different cowpea parts under photoperiod (L:D = 18:6) and continuous darkness (L:D = 0:24). Under photoperiod (L:D = 18:6), oviposition preference ranked as follows: pods (61.7%) > leaves (29.4%) > stems (8.9%). Nymph numbers followed the same order (79.5%, 14.9%, and 5.5%, respectively). Eggs were laid beneath leaf epidermis, concentrated around leaf veins. Under continuous darkness, total nymphs (284) did not differ from photoperiod (L:D = 18:6) (308). The numbers of stem and pod-hatched nymphs were decreased, while the leaf-hatched nymphs increased significantly (46 to 106). In conclusion, M. usitatus prefers pods for oviposition. Darkness does not alter total reproductive output but increases oviposition and hatch rate in leaves, shifting egg spatial distribution among plant parts.