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

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.

Symbiotic ant traits produce differential host‐plant carbon and water dynamics in a multi‐species mutualism

“…First, C. sjostedti ‐removal trees produced much larger crowns than C. sjostedti ‐occupied trees but both groups have low starch concentrations, perhaps because trees prioritize resprouting on damaged branches over starch storage (Smith et al, 2018) after stem‐damaging ants are removed. Second, host trees might metabolize starch stores to produce resin to engulf the stem‐boring beetles (as do pines, Gaylord et al, 2007; Ferrenberg et al, 2014, and East African Acacia xanthophloea : Kahuthia‐Gathu et al, 2018) that C. sjostedti facilitates (Palmer et al, 2008), and the costs of repelling beetles may remain high even after the ant has been absent for years. Longitudinal studies of ant–plant stem starch content before and after colonization by C. sjostedti and similar ant partners in other systems (e.g., Edwards et al, 2009) may help us to attribute depressed stem starch to ant partner traits such as stem cavity excavation or parasite facilitation.…”