Knowledge Gaps, Training Needs and Bio-Ecological Studies on Fruit-Infesting Flies (Diptera: Tephritidae) in Northern Ghana

Abstract

Tephritid fruit flies are a major threat to the horticultural industry in sub-Saharan Africa owing to the heavy losses they cause to fruit and vegetable crops, and the resultant quarantine restrictions. Addressing the fruit fly menace in Ghana requires effective stakeholder training along the fruit value chain, coupled with adequate research information on management strategies. Baseline studies were conducted in northern Ghana to determine the priority management training needs of fruit growers and Agricultural Extension Agents (AEAs), and to document the host range, species composition, seasonal phenology and parasitoid fauna of the pests. The studies involved the use of questionnaire for surveys coupled with a two-year collection and incubation of wild and cultivated fruits from selected sites in the Northern, Upper West and Upper East regions of the country. Fruit growers in all the regions were generally aware that fruit flies were serious horticultural pests responsible for the high losses in their fruit and vegetable production. Fruit growers in the Northern Region were more familiar with the economically important fruit fly species (especially the African invasive fruit fly, Bactrocera invadens) and their damage impact, compared with those in the other regions. Even though basic control practices were adopted by some farmers, a significant proportion of the growers took no action to control the pests. Recommended fruit fly control strategies such as pheromone trapping, bait application, soil inoculation and biological control were virtually unknown to the growers, with the majority of them resorting to the application of unprescribed chemicals with potential environmental and health risks. AEAs demonstrated fair knowledge in majority of the competency aspects of the pests. The top 5 competency areas in need for further training of AEAs included; knowledge of the economically important species, their economic impact, life cycle, host plant associations and control strategies.

Out of 80 plant species studied, 65 (81.5%) of them were positive to 10 different fruit fly species. Eleven (11) plant species were reported for the first time as hosts to B. invadens, while two fruit fly species (Dacus ciliatus and Trirhithrum nigerrimum) were identified for the first time in the area. Ceratitis cosyra and B. invadens were the dominant fruit fly species recorded. Infestation by B. invadens was higher in commercial fruits while C. cosyra dominated in the wild hosts. Among the commercial fruits, infestation was highest in mango (Mangefera indica L), green pepper (Capsicum anuum L.) and water melon (Citrulus lunatus Thunb.), whereas sour sop (Annona senegalensis Pers.), tropical almond (Terminalia catapa L.), syncomore fig (Ficus syncomosus L.), African peach (Sarcocepholus latifolium Smith.), sheanut (Vitellaria paradoxa C.F. Gaertn.), persimmon (Diospyros mespiliformis A. DC.), icacina (Icacina senegalensis Juss.) and albarillo (Ximenia americana L.) dominated the wild host flora. The dynamics of emergence of B. invadens and C. cosyra fluctuated at various levels in response to the availability of host fruits and the influence of air temperature, relative humidity (RH) and precipitation, with precipitation showing the strongest influence. Four species of larva-pupal braconid parasitoids were reared from 14 fruit species that hosted C. cosyra and B. invadens. The parasitoids included Fopius caudatus (Szépligeti), Psyttalia cosyrae (Wilkinson), P. concolor (Szépligeti) and Diachasmimorpha fullawayi (Silvestri). The most abundant and diverse parasitoid was F. caudatus (61.0 %) while the least abundant was D. fullawayi (7.7 %). The overall mean parasitism level was 7.1 % with the highest record in sour sop, African peach and icacina. The peak occurrence of the parasitoids was on June and July, which coincided with the peak of the rains and maturity period of many of the surveyed crops. It is important to train fruit growers on the basic expertise to help address the fruit fly menace in the area. Also, professional capacity development programmes for AEAs should look into how the 5 critical educational needs on fruit fly pests (namely knowledge of the economically important species, their economic impact, life cycle, host associations and control strategies) can be addressed in training workshops. The widespread availability of host plants and the diverse fruit fly species call for particular attention to their impact on commercial fruits, and development of management strategies against these economically important pests. An understanding of the occurrence periods of the different potential hosts and their influence on the population patterns of B. invadens and C. cosyra is also necessary for the development of sustainable IPM programmes. Finally, this study presents the first inventory of parasitoid fauna of major tephritid pests in the area, providing critical baseline data for future conservation or introduction of parasitoids for biological control efforts in the Ghana.