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Wide ranging insect infestation of the pioneer mangrove Sonneratia alba by two insect species along the Kenyan coast
Jenoh, E.M.; Robert, E.M.R.; Lehmann, I.; Kioko, E.; Bosire, J.O.; Ngisiange, N.; Dahdouh-Guebas, F.; Koedam, N. (2016). Wide ranging insect infestation of the pioneer mangrove Sonneratia alba by two insect species along the Kenyan coast. PLoS One 11(5): e0154849. dx.doi.org/10.1371/journal.pone.0154849
In: PLoS One. Public Library of Science: San Francisco. ISSN 1932-6203, more
Peer reviewed article  

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Keyword
    Brackish water

Authors  Top 
  • Jenoh, E.M., more
  • Robert, E.M.R., more
  • Lehmann, I.
  • Kioko, E.
  • Bosire, J.O.
  • Ngisiange, N.
  • Dahdouh-Guebas, F., more
  • Koedam, N., more

Abstract
    Biotic interactions such as insect infestations may damage organisms but they also play their role in ecosystem processes. Insect defoliators and woodborers, including beetles, moths, and horntail wasps, are widely recognized as agents of ecosystem disturbance that can influence forest production and nutrient cycling. Insect infestations can create large-scale forest diebacks. Infesting insects feed and make their homes on bark, trunks, and branches of trees and shrubs. Insect borers damage plants by tunneling through the inner bark and cambium; if the stem is completely girdled, the plant dies at or above the damaged site. If the tree is weakened structurally, leaves and branches may fall. Insect damage can severely affect the quality of timber, and render trees susceptible to disease and secondary fungal infestation. As resources are reallocated to compensate for herbivore damage, the productive capacity of a tree may be reduced. Insect infestation is a scientifically neglected problem in mangrove research and management. This is partly due to the perception that the tannins in mangroves render them inedible to most herbivorous insects, and that tidal flooding inhibits insect population growth. Consequently, insects that attack mangroves are understudied, with a few exceptions. Insect infestations in mangrove forests in the Western Indian Ocean (WIO) region have not been well-documented, though several outbreaks have occurred in this area. For instance, in 2003, substantial stands of Rhizophora mucronata Lamk. were defoliated in the Pemba region of Tanzania. In Kiunga and Lamu, where the largest contiguous mangrove forests of Kenya are found, an unknown insect pest is thought to be responsible for the dieback of R. mucronata over the last two decades. However, this infestation has never been studied. A 2005 survey reported a decline of Sonneratia alba J. Smith due to an insect infestation that rapidly spread northwards towards the mangroves of Somalia. This infestation was attributed to a cerambycid beetle and a metarbelid moth, the taxonomic status of which is currently under revision. In Kenya, these insects are reported to have an overlapping geographical range, but they appear in different locations on the host trees.The symptoms of infestation in S. alba populations suggested that more than one insect species infests S. alba. To date, there exist insufficient and conflicting reports on the identity of these insects, their spatial distribution and biology, and the extent and severity of infestation. This study reports on the identity of the insects, their distribution along the Kenyan coast, and the level and extent of the infestation of S. alba populations. It is hoped that this information will contribute to the development of management and conservation strategies for the East African mangrove ecosystem and generate further insight into plant-herbivore relations in these particular assemblages.

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