Population dynamics of pine woolly aphid, <i>Pineus pini</i> (Gmelin) (Hemiptera: Adelgidae), in Kenya
Abstract The population dynamics of Pineus pini (Gmel.) was examined in two locations in the Kenya Highlands where the mean annual precipitation ranges from 620 to 1400 mm. Variations in population densities were related to rainfall. Generally, there was a marked decrease in population during the three months of heavy rainfall in March to May and a significant increase during dry weather from August to October. This was followed by a slight decrease in the rate of population build-up, until the long rains in April again resulted in another population collapse. Nine species of predatory insects were identified, and population fluctuations of the most common of these, Exochomus spp., was studied. Predators seemed to remove about 12% of the aphid population. Other mortality factors included heat and crawler dispersion. The greatest mortality occurred early in the life-cycle and was mainly due to eggs and crawlers being washed off the host-tree by rain.
¤ Open Access
Effect of variety and planting date of rice on population of natural enemies of brown planthopper, Nilaparvata lugens (Stal)
The present study on the effect of variety and planting date of rice on population of natural enemies of brown planthopper, Nilaparvata lugens (Stal) showed that during August, the mean population of spiders was statistically on par on CSR 30 and PR 114. The population differed with dates and was significantly (p=0.05) higher (9.0/10 hills) in D2 during 2011 only. There was no significant difference in the population of spiders on two varieties and dates of transplanting during September 2011 only. However, significantly higher population of spiders was recorded in variety PR 114 (21.65/10 hills) and D2 (20.52/10 hills) than on CSR 30 (13.67/10 hills) and D1 (14.80/10 hills) during September, 2012. The mean population of spiders did not differ significantly with the dates during October, 2011 and 2012. However, it was significantly higher on variety PR 114 (27.65/10 hills) than on CSR 30 during both the crop seasons. Mirid bugs did not appear in the month of August, 2011 and 2012 whereas during September 2011, the variety CSR 30 and D1 registered significantly higher population than other variety and date. However, a reverse trend was observed with varieties and dates during 2012. The mean population of coccinelid, carabid and staphylinid beetles remained very low on both the varieties in the month of August during 2011 and 2012. However, the population of these predators was influenced significantly by the varieties and dates during 2012. The population of nymphal-adult parasitoids also remained very low during both years and was not influenced by varieties and dates.