Diversity and population dynamics of bactrocera invadens and other tephritid fruit fly species infesting mango (mangifera indica) in Zimbabwe and relative efficacies of selected insecticides incorporated in food baits

Abstract

Studies were conducted from November 2013 to October 2014 in Zimbabwe to determine the temporal population dynamics of the invasive fruit fly pest Bactrocera invadens (Diptera: Tephritidae), to determine the pest’s host range and incidence and to evaluate its control using a food bait consisting of protein hydrolysate and each of the insecticides dimethoate (Dimethoate 40® EC), malathion (Malathion 50® EC), trichlorforn (Trichlorfon 90® SP), deltamethrin (Deltamethrin 2.5%® SC) and lambda-cyhalothrin (Lambda-cyhalothrin 50® EC). Fruit fly temporal dynamics studies were conducted in Mutoko, Murewa, Domboshava and Seke using methyl eugenol-baited traps while host range and incidence were assessed through “fruit rearing”. At each of the four locations (intensive study sites), fruits sampled from mixed mango varieties every two weeks were held in the laboratory at room temperature to determine the associated fruit fly species spectrum. As further confirmatory tests on host fruit and fruit fly species associations, a once-off extensive fruit survey covering the areas in which traps were located as well as outside them was conducted. Overall, there was a significant site x month interaction, with the highest catches of (over 3,400 in February 2014) being recorded in Murewa between February and April 2014. The lowest catches (below 25) were recorded in Seke and Domboshava in October 2014. The highest fruit fly diversity was recorded in Murewa, Seke and Domboshava where, in addition to B. invadens, Ceratitis cosyra and Ceratitis rosa were also recorded infesting mangoes. In the extensive surveys, Harare and Mahusekwa had the highest fruit fly diversity, recording three fruit fly species (B. invadens, C. cosyra and C. rosa). The highest B. invadens fruit infestations were recorded from stringless mango fruits collected in Guruve, which had an infestation rate of 80.5%. No B. invadens infestations were recorded from fruits collected in Chegutu, Zvimba and Buhera. The mango seed weevil, Sternochaetus mangifera, which is a quarantine pest of mangoes worldwide, was also recorded from all the four trapping locations, with Mutoko having the highest infestation rate of 22.5%. In laboratory studies to assess B. invadens control using various insecticides incorporated in hydrolysed protein food baits, Trichlorfon 90® SP (a.i. trichloforn) gave the highest adult fruit fly mortality (87.5%) while Dimethoate 40® EC (a.i. dimethoate) was the least effective with mortality of 40%. vi In conclusion, this study demonstrated that though B. invadens occurs throughout the year, populations are at their highest from January to April. Its abundance is greatly influenced by location. Trichlorfon 90® SP and Deltamethrin 2.5%® SC (a.i. deltamethrin) have the potential to be used as fruit fly killing agents in case of non- availability of malathion which is the traditional fruit fly insecticide that is incorporated in food baits in Zimbabwe. Further local studies on B. invadens biology, overwintering mechanisms and behaviour are recommended so as to generate information that, when combined with results from the present study, could be useful in coming up with ‘smart’ strategies for the management of the pest in specific localities.