Distribution and Abundance of Pine Needle Aphids (Eulachnus rileyi Williams) and Their Potential Natural Enemies on Pine Tree Species (Pinus patula and Pinus elliottii) at Sao Hill Forest Plantation, Tanzania

Abstract

A study was conducted at SHFP, Tanzania to assess the distribution and abundance of PNA and their potential natural enemies. Systematic sampling was used to select every 5th tree along the row of the particular compartment. Five shoots were randomly cut from lower, middle and upper crown parts of each selected tree for laboratory analysis. Data analysis was performed using R and Excel, with normality and homogeneity of variance checked using Shapiro-Wilk and Levene’s tests, respectively. Results revealed that PNA was un-equally distributed throughout the divisions, trees species and age classes at SHFP. The abundance of adult aphids per twig was 7.6 and 12.9 for Division II and III, respectively and was significantly different. Similarly, the mean abundance of eggs and nymphs per twig were 5.5 and 12.2 in Division II and 9.2 and 21.1 in Division III, respectively. Nymphs were more abundant than eggs and adults, while eggs were the least abundant across all examined pine species and age classes. The abundance of adult aphid was 19.6 and 7.0 for P. elliottii and P. patula, respectively and was significantly different. For P. patula, the abundance of adult aphid per twig was 7.3, 8.5 and 5.1 for young, middle and old age classes respectively. In P. elliottii stands, the abundance of adult aphid population per twig was 23.2 and 17.9 for middle and old age classes respectively. The middle part of the tree crown had the highest aphid abundance for both tree species and age classes. Three main natural enemies were identified: Coccinellid beetles (Coleoptera: Coccinellidae), Spiders (Arachnida) and Stink bugs (Pentatomidae), but their numbers were low. The correlation between the abundance of PNA and natural enemies was weakly positive (Rho = 0.0859) but statistically significant (p = 0.035). Tending operations i.e. thinning, weeding, pruning, and regular insect survey and monitoring programs, are recommended to mitigate favorable conditions for aphid growth. Additionally, the SHFP management team should reconsider the introduction and release of Tetraphleps raoi or other predators as biological control agents over large area to increase the current stock of the natural enemies as there were no introduce natural enemies found in the plantation