Morphology, Biology and Semiochemical Mediated Behaviour of the Coreid Bug Pseudotheraptus Wayi Brown 1955, a Major Pest of Cashew In East Africa

Abstract

The coreid bug, Pseudotheraptus wayi Brown 1955 (Heteroptera: Coreidae), is a major pest of cashew in East Africa. Effective environmentally sound management strategies for this pest are still lacking. This study aimed at elucidating the chemical communication system of P. wayi and, identifying semiochemicals that can potentially be developed into lures for use in integrated management of this pest. To achieve this, pre-requisite studies on the morphology of immatures to facilitate effective identification of this pest in the field, evaluation of French bean pods for suitability for mass rearing of the insects and diel behavioural patterns of the species to guide semiochemical bioassays were also carried out. Morphometric measurements were carried out using a Leica® Microsystems EZ4D microscope connected to a computer using the recommended Leica® Application Suite Software. The suitability of French beans for mass rearing of P. wayi and its diel behavioural patterns were determined by observation of the biology and behaviour of the insects on French bean pods in the laboratory. Candidate semiochemicals were identified by olfactometry, EthoVision XT digital video recording of insect behaviour, gas chromatography-electroantennographic detection and gas chromatography-mass spectrometry. The study has shown that immatures of this pest have unique morphological features, the knowledge of which can facilitate effective identification of the insects in the field. It has also demonstrated that French beans are more suitable for mass rearing of this species than coconut and cashew which have been used previously but were unavailable in Nairobi, Kenya where this study was carried out, and can be scarce and too costly. In addition, the study has revealed that peak mating in this species occurs at mid scotophase, and more mating incidences take place during scotophase than photophase; peak oviposition occurs at late photophase with another minor peak at late scotophase, and more eggs are laid during photophase than scotophase; peak nymphal feeding occurs between 18:00 and 0:00 hours, with more nymphs feeding during scotophase than photophase; and adult feeding pattern is unaffected by time or light and darkness. This knowledge was useful for proper timing of behavioural bioassays, and may also be applied in proper timing of control interventions in the field. Finally and most importantly, three chemicals namely (Z)-β-ocimene, (E)-β-ocimene and allo-ocimene were identified from cashew volatiles as attractants for male P. wayi; while hexanal, hexyl acetate and hexyl hexanoate in the natural ratio as in male volatiles facilitate recognition of males by either sex, eliciting attraction in females but repellence in males. These candidate semiochemicals offer opportunities for trapping P. wayi in the field.