Contribution of natural enemies and weather to the population buildup of Raoiella indica on coconut

Abstract

Population dynamic studies help understand how biotic and abiotic factors can affect pest populations and their natural enemies. The red palm mite, Raoiella indica Hirst (Acari: Tenuipalpidae), is an invasive species that severely damages coconut and banana trees and threatens several Arecaceae species in the Americas. In the present study, populations of R. indica were monthly monitored for 16 months in a coconut plantation in Boa Vista, Roraima, Brazil, to evaluate the contribution of natural enemies and climatic factors on population dynamics of this pest. Linear models were adjusted to determine how average air temperature, relative humidity, rainfall, and predators affect the abundance of R. indica over time. Rainfall and high air temperatures were the main factors reducing R. indica populations. During the drier months of the year, from September to March (average temperatures approximately 27.6 ºC), the densities of R. indica were highest, and severe damage, such as yellowing and leaf necrosis, was observed on the plants. The most abundant predator was Amblyseius largoensis (Muma) (Acari: Phytoseiidae). Its density was positively influenced by R. indica and negatively affected by rainfall and high temperatures. Furthermore, the population of A. largoensis was reduced in drier periods and grew slower than R. indica after this period; thus, studies evaluating the release of this predator at the beginning of the rainy season are necessary to assess its effectiveness in regulating R. indica. This is the first report of insect predatory insects, namely Stethorus sp. (Coleoptera: Coccinellidae) and Thysanoptera: Phlaeothripidae, regulating R. indica in Brazil.