Behavioural Bioassays and Identification of Cashew Leaf and Stem Volatiles Mediating Attraction to the Stem Girdler, Analeptes trifasciata (Coleoptera: Cerambycidae)

The cashew stem girdler, Analeptes trifasciata Fabricius (Coleoptera: Cerambycidae), damages cashew by its girdling activities in the stem thereby causing huge economic losses. The stem girdler is managed through cultural practice of burning girdled stems and beetles, though this has drawbacks. The objective of this study was to explore the cues mediating attraction to the cashew host plant;hence the role of olfaction in host plant location by A. trifasciata underlying the semio-chemical option for controlling this insect pest. A diffusional Y-tube olfactometer was used to study the behavioural response of A. trifasciata, to freshly cut cashew stem and leaves odour sources. Methanol-extract of these plant tissues was subjected to the coupled gas chromatography-mass spectrometry (GC-MS) analysis. Y-tube olfactometric assays demonstrated that both sexes oriented towards and spent significantly more time in stem odour arm compared to the leaf odour arm in both male (male: t = 2.228, d.f = 11, P = 0.040) and female (t = 2.341, d.f = 11, P = 0.040). A combination of fatty acids, amino acids and carbohydrates were detected in cashew stems. Some of these fatty acids are attractants to other insect pests. It is suspected that these fatty acid blends may possibly be responsible for facilitating host plant location by both sexes. In conclusion, both sexes were independently and strongly attracted to the stem volatiles;this study opens the possibility of utilizing cashew stem volatiles as surveillance and control tools.

The Discovery of a Green Wood Beetle Diastocera trifasciata(Coleoptera:Lamiinae)on Mango Tree in South Sudan

The green wood insect beetle which was later identified as Diastocera trifasciata((Fabricius)-tribus Ceropplesini,Coleoptera:Lamiinae)was found on September 18,2015,girdling a mango twig at Dr.John Garang Memorial University of Science and Technology(Dr.JG-MUST)campus,Bor county,Jonglei state,Republic of South Sudan.The beetle D.trifasciata attacks young vigorous growing mango branches of more than 20-35 mm circumferences.Severely cut branches dried up and broken away especially when there was a strong blowing wind or just remained dry,hung on the tree.Although this incidence may seem not to pose a significant economic threat at the moment,the authors keenly advocate for proactive pest surveillances,monitoring and evaluating its spread,impact damage level caused on mango plants in most areas of high mango productivity and developing control strategy that will prevent further devastations of mango trees,guarantee high fruit yields and ensure food security in South Sudan.