Insects Associated With Citronella In South-Eastern Ghana, With Particular Reference To ShootborersInsects Associated With Citronella In South-Eastern Ghana, With Particular Reference To Shoo

ABSTRACT Insects associated with citronella were surveyed in the south-eastern part of Ghana for 11 months. Using two different sweep nets, intensive and extensive surveys showed that the foliage of citronella was associated with a diverse insect fauna comprising 10 orders and 102 families as follows: Hymenoptera (29), Diptera (32), Homoptera (8), Hemiptera (12), Coleoptera (10), Dictyoptera (2), Orthoptera (3), Lepidoptera (2), Dermaptera (1), and Neuroptera (3). The shoot of citronella was found to be damaged by dipterous shootflies (Fam: Chloropidae and Fam: Lonchaeidae) and lepidopterous stemborers (Fam: Pyralidae and Fam: Noctuidae). There was no significant difference (P > 0.05) between the mean percentage infestation by the shootflies (mean =1.18%) and that of the stemborers (mean = 0.59%). The chloropid shootflies were identified as Scoliophthalmns micantipennis Duda, Scoliophthalmus trapezoides Becker, Anatrichus pygmaeus Loew, Aprometopis flavofacies Becker, Elachiptera occipitalis Becker, and unidentified species. The lonchaeid shootfly was Silbapectita McAlpine. The pyralid and noctuid stemborers were Eldana saccharina Walker and Sesamia sp, respectively. Whereas S. micantipennis, A. flavofacies were found to cause primary damage by attacking fresh stems, S. trapezoides caused both primary and secondary damage by attacking fresh as well as already infested stems. The status of the other chloropids and the lonchaeid was not clear, since they were always found in association with other insects in already infested tillers. The lepidopterous stemborers were also found to cause primary damage. The larvae of the stemborers attacked the lower part of the tiller and tunnelled a length of 75.40 ± 12.79 mm while the shootflies tunnelled 32.60 ± 3.90 mm. The larvae live inside the tillers and so can possibly be controlled by systemic inseticides. Preliminary field investigation showed that the worker caste of unidentified termites attacked the roots and stems of citronella, and this invariably led to complete death of the plant. This was more prevalent in farms older than one year; for example, 85.7% of the termite infested farms were older than one year. Farmers should therefore not cultivate one farmland for too long. Further investigations showed negligible symptoms of feeding activities of insect foliage pests. For example, less than 0.005%, 0.002% and 0.009%, showed necrosis, curling and defoliation respectively, from insect attack in any farm. Investigation of the seasonal variation of shootborer infestation of citronella showed two possible peaks: one between February and March, and another around October for both the lepidopterous stemborers and chloropid shootflies. The synchronisation in the build up of the damage by both groups of shootborers shows that they can be controlled simultaneously. Percentage 'deadheart' caused by lepidopterous stemborers had a weak linear relationship with rainfall: y = 0.0017x + 0.6298. That by the dipterous shootflies also had a weak linear relationship with climatic factors as follows:- rainfall: y = -0.0024x + 1.3413; evaporation: y = -0.8958x + 2.2639; temperature: y = -0.5826x + 17.15; and relative humidity: y = 0.1292x - 9.8968; where y = percentage deadheart' and x = climatic factor. Comparision of sampling, using only visual 'deadheart' symptom and random dissection, showed that using only 'deadheart' symptom underestimated the infestation of shootborers by 31.8%. Shootborer infestation should therefore be determined from random dissection of tillers. The pupa of female S. micantipennis measured 3.32 + ,08mm in length (n=30) and pupal period averaged 6.72 + 0.39 days (n = 22). The male pupa measured 3.16+_.07 mm long (n = 30) and the mean pupal period was 7.24 + 0.05 days (n = 17). The adults of both sexes lived for about the same period: 8.59 + 0.77 days (n = 29) for the female and 9.41 + 0.60 days (n = 24) for the male. The adults exhibited sexual dimorphism with respect to their total body lengths, the male being shorter (1.90 ± 0.02mm; n = 30) than the female (2.98 + 0.03mm; n = 31)