Evaluation of introduced parasitoids against bactrocera Invadens and their interaction with bactrocera Invadens natural enemies

Abstract

The invasive fruit fly Bactrocera invadens (Drew, Tsurata & White 2005) is causing extensive socio-economic losses in West Africa as a pest in mango production. In addition to reducing crop quality and decreasing fruit production, the presence of the fruit fly has detrimental impact on the export market due to international trade restrictions. To manage the damage being caused by B.invadens to the mango industry in Africa, an Integrated Pest Management (IPM) strategy with biological control as one of its components was initiated by the African Fruit Fly Programme (AFFP) based at ICIPE. To this end, Fopius arisanus (Sonan) and Diachasmimorpha longicaudata (Ashmead) were introduced into Kenya for potential releases. A survey of indigenous tephritid parasitoids in the major mango growing provinces in Kenya was carried out as a first step to identify native parasitoids that are likely to interact with the introduced ones when released. Furthermore, studies on the performance of the introduced parasitoids on B. invadens reared on different host fruits, their thermotolerance levels as well as interaction with other indigenous natural enemies were conducted. A survey of indigenous tephritid parasitoids in the major mango growing provinces yielded several hymenopteran parasitoids belonging to four main families; Braconidae, Eulophidae, Chalcididae and Ichneumonidae. The family Braconidae accounted for the majority of parasitoids recorded with Psytallia as the dominant genus. Results of fruit fly species identified from the surveys confirmed B. invadens as the dominant fruit fly pest in the major mango growing areas in Kenya though members of the genus Ceratitis, Trirhithrum and Dacus were present in the general population. The effect of temperature on the developmental period, longevity and parasitism rates of F. arisanus and D.longicaudata reared on B. invadens was also investigated. A temperature range of 20-30 °C was suitable for the rearing of both parasitoids. Temperatures below 20 °C and above 30 °C were found to negatively affect parasitism rates. Based on a combination of short developmental time and higher parasitism rates, the optimum temperature for the mass rearing of F. arisanus and D. longicaudata on B. invadens was 25 °C. Temperature also had a significant effect on adult longevity of both parasitoids, with longevity highest at 15 and 20 °C compared to the other constant temperatures. The effect of host fruit substrate on the preference and performance of F. arisanus and D. longicaudata was assessed through a range of experiments in the laboratory.Females of F. arisanus preferred mango compared to pawpaw, citrus, guava, marula and tropical almond in choice bioassays. For D. longicaudata, citrus was the most preferred fruit. Parasitism rates for both parasitoids were significantly higher on mango and pawpaw. Finally, interactions involving O. longinoda, B. invadens and F. arisanus and the implications of these interactions were studied through a range of laboratory experiments. Searching and/or oviposition by B. invadens females and the number of eggs deposited in mango domes decreased significantly as ant density increased. Direct interactions between B. invadens and O. longinoda under laboratory conditions primarily consisted of disturbance and deterrence, but predation was hardly observed. The number of F. arisanus females searching and/or ovipositing in mangoes infested with B.invadens eggs also decreased significantly with increasing ant density. Direct interaction between F.arisanus and O. longinoda under laboratory conditions primarily consisted of disturbance, deterrence and predation. Mortality of F. arisanus females due to predation by O.longinoda was significantly higher at higher ant densities. Ant cues or pheromones also had a negative effect on searching and/or oviposition by F. arisanus. The information generated in this study should serve as a guide for the future mass rearing and field releases of F. arisanus and D.longicaudata for the management of B. invadens in Africa