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Journal of Applied Sciences & Environmental Management, Vol. 9, No. 1, 2005, pp. 19-23 Characterization and Preferred Oviposition sites of Atherigona
orientalis (Schiner) on Nigerian Pepper Fruits
1OGBALU, O K; 2EMELIKE, N J T; 3AMACHREE, E I; 3UCHE, F; 4THOMAS, C N 1Department
of Applied and Environmental Biology, RiversStateUniversity of Science and Technology,
Nkpolu, Port
Harcourt Code Number: ja05004 ABSTRACT: The pepper fruitfly, Atherigona orientalis (Schin.) has been considered and accepted as a potentially serious and important pest of pepper fruits in Nigeria. Females of A. orientalis oviposited on fruits of pepper (Capsicum species) both in the laboratory and in the field. Oviposition commenced about 2 weeks after fruiting and increased with rainfall. Six pepper cultivars were used for this study and parts of pepper fruits utilized as oviposition sites were calyx, grooves, blossom ends and receptacles in most of the cultivars. Records of the number of eggs isolated from the aforementioned portions of the fruits were made. Oviposition response of A. orientalis females was different on the four parts of pepper fruits. Statistical analysis showed significant differences on the number of eggs deposited on the calyx, grooves, blossom ends and receptacle of the six pepper cultivars. On sites that were preferred for oviposition, most of the eggs were collected from the calyx (40-75%) followed by the grooves. Significantly lower numbers were collected from the blossom ends or receptacles depending on cultivars. @JASEM
MATERIALS AND METHODS Seeds of six cultivars of pepper were separately sown in 50cm rows in wooden trays (60 x 45 x 10cm) in the greenhouse. The seedlings were transplanted to the field five weeks later at a spacing of 60 cm within and 90 cm between rows. Each plot consisted of five plants of a particular variety and was separated from other plots by a 1-metre gap. Each of the six varieties of pepper (Nsukka yellow, Atarugu, Tatashi, Sweet pepper, Birds eye chilli and Local medium red) was replicated five times in a randomized complete block design. 15g of N.P.K. (15:15:15), compound fertilizer were applied to each plant as a side dressing two weeks after transplanting. At two weeks after fruiting, from each of the experimental plots, 15 fruits were randomly plucked from the plants in the three inner rows (i.e. one fruit per plant for each of the five plants per row. Sampling was carried out at fortnightly intervals for four months. In the laboratory, the fruits were examined for eggs using the M7 stereomicroscope. Records of eggs isolated from different parts of pepper fruits were made. RESULTS AND DISCUSSION The oviposition response was different on four parts of pepper fruits (namely calyx, grooves, blossom ends and receptacle) of the six pepper varieties. The calyx proved the most preferred oviposition sites. On the calyx, Nsukka yellow had 5468 (55.06%) eggs followed by Atarugu with 3709 (37.35%) (Tables 1 and 2). No eggs were recorded on Birds eye chilli and the Local medium red varieties at this region. The trend was the same for the number of eggs on the grooves except that the Local medium red variety had more eggs than the Sweet pepper. The blossom ends of Nsukka yellow, Tatashi, Birds eye chilli and the Local medium red varieties attracted no eggs. On the number of eggs from the receptacle, the trend was the same as the number of eggs found at the calyx for all the varieties. The blossom ends of some pepper varieties attracted A. orientalis females hence up to 72.47 number of eggs were deposited on Atarugu variety that have reasonable indentation at the blossom ends (Table 2). Pointedness is usually most pronounced in Nsukka yellow, Birds eye chilli and the Local medium red (Ogoni pepper) varieties and the blossom ends of Atarugu, Tatashi and Sweet peppers vary in their degrees of indentations (Table 2). Statistical analysis showed significant differences in the number of eggs deposited on the calyx, grooves, blossom ends and receptacle (Table 3). Significant differences existed between the number of eggs deposited on the calyx of Nsukka yellow, Atarugu, Tatashi and Sweet pepper. The number of eggs on the grooves of Nsukka yellow, Atarugu, Tatashi and Birds eye chilli varieties significantly differed from each other at both 1% and 5% level (DMRT). No significant difference existed between the number of eggs deposited in the grooves of Sweet pepper and Local medium red varieties. The eggs deposited at the blossom ends of Atarugu variety was significantly different from those deposited at the blossom ends of Sweet pepper and both significantly differed from those of Nsukka yellow, Tatashi, Birds eye chilli and Local medium red varieties. For the receptacles, even though there was no significant difference between the Birds eye chilli and Local medium red but both significantly differed from the rest of the varieties at both 1% and 5% levels. Furthermore, testing for significant difference in oviposition sites (Table 4), the number of eggs deposited by A. orientalis females on the various parts of pepper fruits significantly differed from each other in most of the varieties. No eggs were recorded on any parts of the fruits of the Birds eye chilli variety. There was no significant difference between the number of eggs deposited on the calyx, blossom ends and receptacle of this variety. However in the Local medium red variety there was significant difference in the number of eggs laid in the grooves and other sites. In the Atarugu variety the number of eggs deposited on the various sites significantly differed from one another. The trend in Nsukka yellow followed the same pattern as in the Tatashi variety with significant difference existing in the number of eggs deposited at various sites. Also the trend was the same in both the Sweet pepper and Atarugu varieties. Means in the same column and followed by different letters are significantly different from each other (DMRT, P< 0.05). *No eggs were recorded on Birds eye chilli variety. Figure in the column not followed by the same letters are not significantly different at 1% and 5% (DMRT). The ovipositional difference in the six varieties of pepper implies that certain morphological attributes inherent in some of them must have contributed to their preference/non-preference. This agrees with earlier contributions that plant characters are responsible for the behaviour of most phytophagous insects during orientation for food, shelter and oviposition (Kumar, 1984). The eggs of A. orientalis were meticulously their inserted under the calyx during oviposition by the females showing a very organized egg-laying habit and pattern. Pepper varieties with raised or open calyx were with more eggs. Both the Nsukka yellow and Atarugu varieties have raised calyx (Ogbalu, 1989). The females also utilized grooves (even when cracked) as ovipositiion sites and therefore pepper fruits with cracks attracted more eggs (Ogbalu, 1986). Eggs were also found at the blossom ends (that had reasonable depths to sustain eggs) and a few on the receptacles of some varieties. Varieties such as the Birds eye chilli and Local medium red have acquired tight and closed calyx and both lack depth in their blossom ends (they have sharp and pointed blossom ends). Morphological factors such as size, colour, shape, nature of calyx (whether raised and /or open), presence/absence of grooves and fleshiness of the mesocarp (which provides immediate food for the emerging first instar larvae) must have contributed for the choice of a particular variety by the females during oviposition. It is therefore likely that small size, absence of grooves, colour (red), closed calyx, thin epicarp and non-fleshiness of the mesocarp of the Birds eye chilli variety are factors which contributed to the non-preference of this variety for oviposition (Ogbalu, 1989). On the other hand in Nsukka yellow, the presence of grooves, its raised calyx, colour (yellow), the fleshiness of mesocarp and its strong aroma must have contributed to its susceptibility to oviposition. The grooves on the fruits of Nsukka yellow have reasonable depth also the body of the fruits are heavily wrinkled to accommodate more eggs than the Atarugu and sweet pepper varieties. Generally the choice for oviposition sites determines and serves as immediate feeding sites for the emerging first instar larvae. The overall surface morphology and characterisics of pepper fruits influence their choice as oviposition sites, hence A. orientalis females show preference to varieties which pepper fruits have raised /open calyx and grooves over varieties that lack these characteristics. Another characteristic that influences the choice for oviposition site or substrate in insects generally is their response to colour of vegetation, the entire crop or fruits. The response to colour plays an important part in food location and selection. In pepper, inspite of the differences in colour, shape and texture of fruits, also even with the manipulation of both visual, aroma or odour cues, the selection of pepper fruit as oviposition substrate and different parts of it as ovipositon sites by A. orientalis females was uniform and purposeful. All pepper varieties that possess the same morphological attributes (raised/open calyx, grooves (wrinkled/ridged) and blossom ends (with indentation), etc-attracted eggs depending on the number of oviposition sites. Such oviposition sites provided immediate feeding sites for the emerging larvae as they bore their way into the fleshy mesocarp of the fruits (Ogbalu and Okwakpam, 1996). Disturbed females must have discharged eggs deposited on the receptacle accidentally and deposition of eggs within the blossom ends occurs only during heavy infestation. High expression of pointedness in the blossom end morphology of Nsukka yellow, Birds eye chilli and Local medium red varieties must have hindered deposition of eggs at this site (blossom end). Varieties such as sweet pepper and Atarugu that have reasonable indentation at their blossom ends attracted eggs under heavy infestation. It is believed that the absence or non -expression of pointedness in these varieties contributed to their susceptibility and utilization as oviposition sites. However the expressivity and inheritance of pointedness in pepper varieties deter the A. orientalis females from depositing eggs at the blossom ends and should be incorporated in breeding programmes where crosses can be made with varieties that have expression of pointedness. Also although varieties that have expression of excessive grooves/wrinkles attract A. orientalis females for oviposition under heavy infestation, these wrinkled surfaces (grooves), which feed on the eggs and larvae of A. orientalis. The provision of such morphological surfaces becomes advantageous in biological control as the spiders spin their webs within the grooves and ridges trapping eggs and larvae and feeding on them. Eggs deposited under calyces had been found hollowed out by spiders. In tomatoes (Lycopersicon esculentum Mill). Barten et al., (1994) were of the opinion that the expressivities of pointed-ness are usually most pronounced in young immature fruit and gradually disappear as fruit matures. In the Nigerian peppers, the expressivities of pointed-ness or indentation of the blossom end is varietal and not age-dependent. With the identification of oviposition sites of the pest on pepper, this study will be of great use for the control of the pest and also to plant breeders in the development of resistant varieties incorporating pointed-ness of blossom ends, flat, tight and fixed calyces (as in Birds eye chilli) in pepper crosses which will deter A. orientalis females from ovipositing on pepper fruits. ACKNOWLEDGMENTS REFERENCES
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