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PROCEEDINGS OF THE 41st ANNUAL SESSIONS OF INSTITUTE OF BIOLOGY, SRI LANKA HELD ON 24TH SEPTEMBER 2021
Can pupal dimensions of Spodoptera frugiperda (Lepidoptera: Noctuidae) be considered
as predictors of sexual dimorphism prior to eclosion?
R.H. Kasige, N. Pallewatta, C.D. Dangalle
Department of Zoology and Environment Sciences, University of Colombo, Sri Lanka.
*cddangalle@zoology.cmb.ac.lk
Sexual dimorphism is a key feature mainly attributed to sexual selection and mating success.
It is considered with importance when initiating management strategies for insect pests as
the knowledge of gender-specific traits at the pupal and adult stages of pests have provided
reliable information to manage pests and forecast outbreaks. Being a deadliest polyphagous
pest of maize and other important crops, the morphology and morphometry of Fall
Armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) have shed light on
successful identification of sex for its effective controlling. Therefore, the present study
assessed variations in size and development duration of the pupal stage of S. frugiperda, to
determine sexual dimorphic characters that could reliably distinguish sex before eclosion.
Over six successive generations of laboratory reared 231 live pupae (141 females and 90
males) were observed for pupal stage duration (days), maximum pupal width (mm) and
maximum pupal length (mm) and were analyzed. According to available literature, the only
morphological feature to distinguish pupal males and females is that male pupae show a short
distance between the genitalia and anal slit which is comparatively longer in the female. Since
this only involves one parameter, other pupal dimensions were considered and thus, this
study reveals that the pupal stage duration of males is significantly different to that of the
females, and have a longer mean pupal duration (7.5 days) compared to the females (6.7
days). Early eclosion in females may increase early fecundity due to prematuration feeding.
Delayed eclosion, may temporarily avoid mortality risks for adult males. Further, the length
and width of male pupae were significantly larger than the length and width of the female
pupae. This can be attributed to higher migratory propensity and flight capability in males.
The study revealed that pupal dimensions and pupal stage duration can be used as predictors
of sexual dimorphism in Spodoptera frugiperda.
Keywords: Spodoptera frugiperda, pupal dimensions, sexual dimorphism, morphometrics