GIS based Infestation Biogeography of Palm Weevils, Pachymerus cardo in the Niger Delta, Nigeria

Abstract

Data on Oil Palm Kernel Borer Pachymerus cardo were compiled from several sites in the Niger Delta at different Euclidean distances ranging from 11-127 kilometers. The monthly infestation rates and location similarity in infestation were examined with univariate non-spatial statistics and geographic information geostatistical tools. The results of the within month abundance of the weevils showed an average and peak infestation rate of (452:800)  in May with a slow increase through the months of June(497:921) to peak values in August (616:1272). This dropped to 578:1206 and 525:924 in September and October respectively. No significant differences within-month mean scores for all the months (p < 0.05) by both the student t and Hsu pair comparisons were observed. Significant differences from univariate non-spatial statistics were however observed in site infestation distribution (p < 0.05) between  Obiozimini, Omerelu,  Ebubu, Omoku, Egbeda and the following sites namely Abuloma, Obowo, Mbieri, Isiala Ngwa, Kaiama, Old  Bakana and between Egbeda and Obiozomini. A scaling of the sites using geostatistics techniques of kriging and inverse distance weighting indicated that geographic association among sites was independent of nearness or distance decay. A spatial autocorrelation analysis at a z-score of 2.98 and 95% confidence rejected the null hypothesis of the cause for the observed distribution to be random. The clustered nature of the weevil pest is attributed to the stable habitat and wide spread of the oil palm which is thriving within the same environmental variables of rainfall and humidity among the sites from where the weevils were collected.

Key words. Oil Palm, Weevil, Pachymerus cardo, GIS, Autocorrelation