Diversity and Seasonal Changes of Scale Insects and Associated Biota on Citrus Trees in Coastal and Lower Eastern Counties, Kenya

Abstract

Citrus farming is a major source of revenue for large and small-scale farmers in Kenya. Despite its importance, citrus production is confronted with threats associated with pests and diseases. Together, pest infestations and disease infections cause a reduction in the quality of marketable produce, resulting to a high produce losses. Management of diseases and pests is thus vital in increasing citrus yield. In the recent past, the management of pests and diseases has solely depended on synthetic pesticides application. This does not only increase the cost of production but also associated with high health and environmental risks. The use of integrated pest management (IPM) has thus been recommended as a more sustainable alternative in the control of diseases and pests. However, knowledge of the pests and associated biota biodiversity is important in the development of any sustainable pest management strategy. A study to determine the diversity of scale insects pests and their associated biota was conducted in four counties: Kilifi and Kwale counties in the Coastal region and in Machakos and Makueni counties in the Lower Eastern counties in July/August (dry season) and in October/November (wet season), 2019. These are main citrus producing ares in the country. The study was aimed at filling the invertebrate diversity knowledge gap in the sample sites. The convenience sampling method was used to select 328 fruit orchards in the four counties. A total of 82 fruit orchards per county that were not more than 5 km on both sides of county main roads were sampled. The farms' selection was based on the availability of 10 citrus plants per farm, the height of the tree (2-3 m), and each farm's distance from the main road. A random sampling method was used to select three citrus plants per orchard, from which samples of scale insects, natural enemies, and ants were collected. The specimens were collected, properly stored, and later transported to the laboratory at the National Museums of Kenya for the identification process. 22 scale insect species were recorded belonging to four families; Diaspididae (hard scales), Coccidae (soft scales), Pseudococcidae (true mealybugs), and Monophlebidae (giant mealybugs). The Diaspididae and Coccidae were the most diverse scale insect families in both Coastal and Lower Eastern regions. In the study, four species of scale insects were recorded in Kenya for the first time; the armored scales; Parlatoria ziziphi (Lucas), Parlatoria pergandii (Comstock), Aonidiella comperei (McKenzie), and a soft scale; Pulvinaria polygonata (Cockerell). The scale insects were closely associated with the predators (coccinellids and lacewings) and attendant ants. Fourteen ladybird beetles and one lacewing species were associated with the scale insects from the sampled sites. Nine ant species in 3 subfamilies were found associating with the scale insects, facilitating pest resurgence. Seasons and regions were found to affect the abundance of scale insect pests and their associated biota in both regions. Some scale insects, attendant ants and predators species showed some varying trends between seasons and regions due to high temperatures and humidity which affected pest development. The information obtained in the study will be useful in the development of efficient control strategies against the scale insect pests improving citrus production in Kenya. The diversity of scale insect pests identified in this study will be useful in plant quarantine facilities to monitor and prevent accidental introduction of exotic-scale insect species.