One hundred and four species of insects in 47 families and 9 orders identified from a set of 15,930 insects in the early- and 7,427 insects in the late-sown roselle plots were collected. Collection from the green-type (13,376) exceeded that from the red-type roselle by 3,391 insects. Eighty-one of the species were phytophagous (Table 1) and 20 species were beneficials (Table 2). Coleopterous (especially Chrysomelidae and Lagriidae) and hemipterous (especially Pyrrhocoridae) insects constituted a high proportion (69.
0 %) of the collections (Fig. 1). Five species (Monolepta thompsoni Allard, Nisotra sjostedti Jac., Lagria villosa F., Oxycarenus hyalinipennis Costa, and Dysdercus volkeri F.) were highly abundant; three species (Asbecesta cyanipennis Har., Carpophilus fumatus Boh., and Earias sp.
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) were abundant; while eleven species (Monolepta goldingi Bryant, Trichispa sericea Gn., Bemisia tabaci Gn., Aphis gossypii Glover, Empoasca sp., Acrida bicolor Thunb., Aidopus thalassinus Fab., Polistes spilophorus Schlett, Cheilomenes sulphurea Oliv.
, Exochomus. Flavipes Thunb., and Pheidole sp.
) were moderately abundant. Among the three categories of abundant species, M. thompsoni, and N. sjostedti were largely ubiquists (having 100 % occurrence) while the others, with frequency of occurrence ranging from > 50 % to < 100 %, were categorized constant species (Dajoz, 2000). Table 3 shows a rich diversity of insects associated with roselle at Makurdi going by Margalef’s and Shannon’s indicies, respectively; however, Buzas and Gibson’s evenness index shows low evenness of the species , i.e.
, the species were not equally abundant. Insect diversity and richness tended to be more on the green-calyx roselle than on the red-calyx, and more in the early- than in the late-sown crop. All parts of the plant, excluding the roots, were colonized by insects (Table 4). Defoliators were preponderantly adult coleopterous insects among which M.
thomsoni, N. sjsostedti, A. cyanipennis, and L. villosa were the dominant species.
They were most abundant at the vegetative growth stage. At reproductive growth stage, both adult and immature stages of insects fed on the crop, the dominant species being D. volkeri, O.
hyalinipennis and Earias sp. The number of insect species collected fluctuated during crop growth but it increased phenomenally attaining a peak at 11 and 13 weeks after planting the early- and the late-crop, respectively (Figs. 2 and 3). Figs.
4 and 5 show temporal spread of the species on roselle. While infestation by M. thompsoni and N. sjostedti straddled the entire growth period, that for A. transversa was limited to the seedling and vegetative stage. DISCUSSIONDaramola (1984) observed 30 species of insects in 15 families and 4 orders infesting roselle in farmers’ fields in southwestern Nigeria.
In their study at Ogbomoso, Olaniran et al. (2013) listed 5 insect pest species in 5 families, and 4 orders. At Samaru, Dike (1992) recorded 11 species in 9 families and 3 orders. A far greater species diversity and richness has been documented in this paper. It is the consequence of a longer duration of observation and collection. Nevertheless, many species reported elsewhere were not found at Makurdi.
These include: Alcidodes grassirostris Thom., Cheilomenes lunata F., Chrysolagria cuprina Thomas, C. nairobana Borch., Cryptocephalus obesus Suff., Diplognata gagates F., Lobotrachelus incalidus Boh., Lycus semiamplexus Murr.
, Nematocerus acerbus Fst., Podagrica uniformis Jac., Pseudagrilus sophorae F., Silidius bennensis Pic., Stictoleis maculata F., Syagrus calcaretus F. Coleoptera; Clavigralla gibbosa Spin.
, Deraeocoris martini Drylocoris sp., Dysdercus superstitiosus F., Locris maculata F., Lygaeus festivus Thunb., Mirperus torridus Wstw., Nagusta sp.
, Oxycarrenus gossypinus Dist., Rhinocoris bicolor F., (Hemiptera); Amascta flavicosta (Lepidoptera) M. thompsoni, N. sjosstedti, the frequently occurring and abundant coleopterous species whose infestation straddled crop growth period, are classifiable as major pests at Makurdi given the extensive leaf perforation noticed particularly at the seedling and vegetative stage and the consequential adverse impact on plant vigour, growth, and yield (Clementine et al.,2009; Ewete, 1978). In southwestern Nigeria Daramola (1984) identified Chrysolagria cuprina Thomas, C.
nairobana Borch, Podagrica uniforma Jac., and Syagrus calcaratus F. as the major seedling and foliage pests.
The dominant insects at the reproductive stage were D. volkeri, Earias sp. and O. hyalinipennis.. This finding is consistent with the reports by Daramola (1984), Ewete and Osisanya (1984), Abdel-Moniem et al.
(2011), and Ottai et al. (2004). Earias larvae perforate the fruit consuming its content and creating portal of entry for secondary invaders. Piercing and sucking of maturing seeds of roselle by both D. volkeri and O. hyalinipennis culminate in seed weight loss and poor germination (Odhiambo, 1957).
Of the 20 beneficial insects documented, 18 were predatory species; P. spilophorus and E. flavipes were the dominant predators in both the early- and late-sown crops. Abdel-Moniem and Abd El-Wahab (2006) had previously identified Polistes sp as a dominant predator in roselle plantings in Egypt.
The coccinelid beetles, C. sulphurea and C. vicina have been reported to prey upon aphids in southwestern Nigeria (Daramola, 1984). The impact of the predators and the only parasitoid found in this study (Iphiaulax sp.) was not determined.
However, the ratio of beneficial insect to pest species was very low. To enhance farm and farmer productivity in roselle cultivation, it is suggested that feasibility of economically controlling the key field pests using synthetic/plant-derived insecticides, varietal resistance and improved crop cultural management practices which conserve beneficials in roselle fields be evaluated.