Biological Studies on Earias Insulana (BOISD.) and Earias Biplaga (WLK) (Lepidoptera: Noctuidae) as Pests of Okro (Abelmoschus Esculentus L. Moenoch) in Nsukka, Nigeria

Abstract

Earias species are serious pests of cotton and other malvaceous plants in the tropics. The biology of &. Snsu1q-m and g, biplam specifically as pests of okro in Nigeria, was investigated in the field and the laboratory from September 1984 - July 1985 at the University of Nigeria, Nsukka, From the laboratory studies, f ecwndity , incubation p e r i d , pre-oviposition period, mean durations of larval and pupal stages, adu1t"longevity as w e l l as the duration of l i f e cycles of the moths were established, Based on frequency distribution of head capsule widths of field-collected and laboratory-reared larvae, and direct count of shed head capsules of these internal feeding larvae, 5 imaginal stages were confirmed for the species. Okro proved to be a suitable alternativg host plant for these mothsytheir l i f e cycles at near natural atmospheric conditions in the laboratory being + + 21-75 - 1.37 days and 26.18 - 2.09 days for g. insulana and E, biplaqa respectively, Besides, larvae fed solely - on okro fruits (seeds) produced viable progeny. Fecundity of these moths + (whose larvae were raised on okro seeds) was very low (8 - 3.77 + and 9.3 - 3.51 eggs for insulana and g, biplaqa respect~vely). x i i In nature -E, .in sulana was most cmmon during the dry season while -Eo biplaqa occurred mostly during the rainy season, Pest ihcidence in the f i e i d , evidenced by larval puncturing of a d entry into okro f r u i t l e t s , commenced a t fruiting and lasted virtually till death of the host plants. Overall damage to unabortecl okro f r u i t s was 23.06% while abortion of f r u i t l e t s resulting from larval attacks amounted t o 10.83%, Consequently it is concluded that these two moth species are normally no serious pests of okro as they are of cotton. The heaviest larval damage of okro f r u i t s during this study occurred about the month of January which coincided with the dry season, while the l e a s t damage occurred about May during the rainy season. The l a t t e r situation fortdtously f i t s i n t o t h e cultural practices of okro farmers of Southern Nigeria, x i i i