Distribution and Seasonal Occurrence of major insect pests of cotton in Uganda

Abstract

Both surveys and field experiments were conducted to study the distribution and seasonal fluctuation of major cotton pests in Uganda. The surveys were carried out in 13 cotton growing districts including; Wakiso, Mpigi, Mukono (Central region), Kamuli, Jinja (Eastern region), Amuria, Amolator, Pallisa, Serere (North-eastern region), Kasese, Nakasongola, Masindi and Kiryandongo (Western region), with laboratory rearing and the field experiment conducted at the national semi arid resources research institute (NaSARRI).Twenty cotton fields were selected from each district in four sub counties, 5 from each sub county giving a total of 260 fields for the study in 2013 and 2014 respectively. Each selected field was visited 3 times in each cropping season i.e. once at vegetative stage, once at Squaring stage and once at boll growth. For 2014 season. Cotton variety BPA2002, was sown on 16th, June, 2014 in plots, measuring 40 x 60 m2 at 4 seeds/hole and soil depth of 2.5 cm. Plant to plant and row to row distances were kept at 30 cm and 75 cm, respectively. Recommended agronomic practices with no pesticide application were applied throughout the cotton season. Densities of insect pests were recorded on ten days interval on randomly selected leaves from top, middle and bottom of the 30 plants selected. The insects were recorded from 2nd week of July till 4th week of November. On each sampling date, bollworm larval densities, Aphid counts, mite counts were evaluated on 20 randomly selected cotton plants per field in both 2013 and 2014 seasons respectively. Boll worm larvae collected were placed in plastic containers, reared in the laboratory until adult emergence, counted and added to the sweep net catches. For aphids and mite records were taken from upper, middle and lower leaves of randomly selected twenty plants (Shah et al., 2015). Adult boll worm moths, stainers and white flies were also collected using a sweepnet, where each field was divided diagonally and in the early morning and late evening insects were collected by sweeping through the field, the catches collected, separated by species, starved to death and then placed in alcohol for further morphological identification. Data was analyzed by ANOVA using general linear model procedures at 5% level of significance. Meteorological parameters like temperature and relative humidity during the study period were recorded. Correlation analysis was made to study the relationship between weather parameters and incidence of major insect pests of cotton by following standard statistical methods For the survey, high aphid occurrences were observed in Kasese, Serere, Wakiso and Mpigi districts respectively, Stainers (Mukono ,Serere, Pallisa and Kasese districts),Mites showed higher occurrences in all the districts surveyed with highest counts of bollworms observed in Kasese and Pallisa districts and for the seasonal fluctuation study, mites (Tetranychus urticae), peaked (38.4 individuals per plant), in the first week of September, Aphids (38 individuals per plant) in the last week of August, White flies (35 individuals per plant) in the last week of August, Jassids (17.5 individuals per plant) in the second week of October, and stainers peaked (10.5 individuals per plant) in the last week of September. In conclusion the districts surveyed appeared to be hot spots for a particular pest and farmers should now employ integrated pest management in order to reduce the pest pressure in their regions. This should be employed with proper timing of when a particular pest becomes a threat to the cotton crop based on the seasonal fluctuation data obtained