Wood-boring beetles associated with Acacia xanthophloea in Nairobi and Machakos Counties, Kenya.

Ruth Kahuthia-Gathu,Duncan Kirubi Thungu,Rachael Kimani,Lucy Wangu

doi:10.1371/journal.pone.0188773

Abstract

Naivasha thorn tree, Acacia xanthophloea, is grown for foliage, timber, shade and rehabilitation of soils in areas with high water tables in Kenya. Its production is threatened by insect pests, which cause major losses. Very little is documented on wood-boring beetles which cause considerable economic damage to lumber used in a variety of applications, and little is known about their natural enemies in Kenya. We conducted the study to evaluate the occurrence of wood-boring beetles on A. xanthophloea in two different regions of Kenya. Infested wood samples of A. xanthophloea with fresh exit holes were collected from three sites in Kenyatta University (KU), Nairobi and Mitaboni in Machakos, Kenya. The samples were placed in clear plastic buckets and kept at ambient temperatures 23±2°C, 65±10% relative humidity and 12L: 12D in a laboratory where they were observed daily for adult emergence. Adult beetles were collected every three days for identification and data recording. The experiment was replicated four times and data collected twice a week for 6 months. Data on abundance was subjected to analysis of variance using SAS software. A total of 5,850 and 4,691 beetles were collected where 2,187 and 3,097 were Bostrichidae, accounting for 37% and 66% in KU and Mitaboni, respectively. A total of 12 bostrichid species was identified, including Sinoxylon ruficorne, S. doliolum, Xylion adustus, Xyloperthodes nitidipennis, Xyloperthella picea, Xylopsocus castanoptera, Lyctus brunneus, Heterbostrychus brunneus, Xylopsocus sp., and Dinoderus gabonicus. The most abundant species in KU was Xylion adustus with 1,915 beetles accounting for 88.4%, and Sinoxylon ruficorne in Mitaboni with 1,050 beetles accounting for 33.9% of the total. Sinoxylon ruficorne was only recorded in Mitaboni while only 2 specimens of D. gabonicus were found in KU. The mean number of exit holes on A. xanthophloea differed significantly between sites, which corresponded approximately to the amount of economic damage caused by the beetles to the structural integrity of the lumber. In addition, a number of predators in the family Cerambycidae, Cleridae, Histeridae and parasitoids from Braconidae, Ichneumonidae, and Chalcididae were recovered, suggesting a need to conduct further studies to document these species' diversity, parasitism rates and efficacy for possible biological control.

Highlights

Acacia xanthophloea belongs to the pod bearing plant family Fabaceae, subfamily Mimosoideae and is commonly known as sulphur bark, Naivasha thorn or fever tree in English, Mgunga in Swahili, and Murera in the Kikuyu dialect of Kenya
The survey was conducted in May 2016 from Kenyatta University (KU) and Mitaboni in Nairobi and Machakos Counties, respectively
Over 5,850 and 4,691 wood-boring beetles were recovered from May 2016 –Feb 2017 from samples of A. xanthophloea collected in May 2016 at KU and Mitaboni, respectively and kept in the laboratory

Summary

Introduction

Acacia xanthophloea belongs to the pod bearing plant family Fabaceae, subfamily Mimosoideae and is commonly known as sulphur bark, Naivasha thorn or fever tree in English, Mgunga in Swahili, and Murera in the Kikuyu dialect of Kenya. Acacia xanthophloea is native to Botswana, Kenya, Malawi, Mozambique, Somalia, South Africa, Swaziland, Tanzania, Zambia, and Zimbabwe [1]. It grows in semi-evergreen bushland and woodland in areas with a high groundwater table near swamps, riverine forests or at lakesides and often forms dense stands in seasonally flooded areas where young branches and leaves are eaten by elephants, leaves and pods by giraffes and velvet monkeys [2]. Several species are grown where foliage and pods provide food for livestock during drought [3, 4]. Many insects in the family, Bostrichidae, are notorious for locating and infesting freshly cut wood [1, 10]. Bostrichid beetles prefer to infest dry wood with relatively low moisture content between 8 and 30% [12,13]

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