Al-Riyami, Abdulhamid
(2022)
Biological control of pomegranate butterfly Deudorix livia Klug (Lepidoptera: Lycaenidae).
PhD thesis, University of Nottingham.
Abstract
This thesis comprises a group of interconnected studies collectively aimed at evaluating and improving biological control of an economically important pest, the pomegranate butterfly Deudorix livia (Lepidoptera: Lycaenidae). In the Al Jabal Al Akhdar, ‘green mountain’ area in Oman, where this study took place, D. livia is attacked by egg parasitoids, principally Telenomus nizwaensis Polaszek (Hymenoptera: Scelionidae) which is indigenous and also two imported species Trichogramma brassicae Bezdenko, and Trichogramma evanescens Westwood, (Hymenoptera: Trichogrammatidae). The first chapter provides an overall introduction to the biology and ecology of the pest and its natural enemies.
In Chapter Two, the species identification of Telenomus nizwaensis is presented. This work was with collaboration of British Natural Museum, and the identification was based on morphology and DNA sequence data. The name ‘Telenomus nizwaensis Polaszek’ derives from the prefix Nizwa, which is the city near to Al Jabal Al Akhdar, and is the capital city of Ad Dakhiliyah Governorate. Chapter Three evaluates the possible differences in host acceptance behaviour and also possible interactions between T. nizwaensis, Trichogramma brassicae and T. evanescens when presented with field-collected D. livia eggs in the laboratory. Telenomus nizwaensis was found to be dominant parasitoid of the field collected host eggs (field parasitism probability = 0.42). In the laboratory presence of T. nizwaensis increased the likelihood of oviposition to 0.67. Survival to adulthood was negatively influenced by the presence of T. nizwaensis or T. evanescens and sex ratio in all three species was female biased. Overall, the experiment suggested that Trichogramma can be disruptive to the pest control that can be achieved by T. nizwaensis.
Chapter Four presents an estimation of the prevalence parasitism by Trichogramma in the agri-field environment. It is concluded that these parasitoids are almost completely ineffective. Emerged parasitoids from collected D. livia eggs were almost exclusively T. nizwaensis. It is concluded that future efforts should focus on encouraging Telenomus rather than using Trichogramma, however, it may also be possible to improve the performance of Trichogramma.
In Chapter Five, effects of biotic and abiotic factors on D. livia oviposition rate and the proportion of eggs parasitised by T. nizwaensis were investigated in the field. It was found that elevation had no effect, although studied orchards were significantly different in terms of oviposition and parasitism rates. In terms of timing, peaks of D. livia oviposition were at end of May and end of June, whereas parasitism by T. nizwaensis peaked in mid to late June. Fruit volume affected oviposition negatively and parasitism positively. Deudorix livia was most attracted to fruits of brownish green colour followed by greenish fruits. Telenomus nizwaensis most often attacked host eggs that were laid on yellow fruits, followed by green fruits. The number of fruits per branch positively affected the number of D. livia eggs laid but not the proportion parasitised. Fruits height from the ground did not influence either oviposition and or parasitism rates. Deudorix livia laid more eggs on fruits growing on the north side of trees than on other sides, followed by the eastern side, but there was no effect of cardinal orientation on the prevalence of parasitism. The cumulative measures ‘Day degrees’ and ‘day relative humidities’ both negatively affected the number of D. livia eggs laid and positively affected the proportion of eggs attacked by T. nizwaensis. The sex ratio of emerging parasitoids was slightly female biased.
Overall, the mix of laboratory experiments, field studies and taxonomic identification presented here contributes to the understanding of the butterfly pest and its associated natural enemies and suggests directions for further work to improve its control.
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