Temperature-dependent phenology of the parasitoid Fopius arisanus on the host Bactrocera dorsalis.

Fopius arisanus (Sonan), an egg-pupal parasitoid of numerous fruit fly species, was recently introduced into Africa for the control of the Oriental fruit fly, Bactrocera dorsalis (Hendel). In this study, life-table data of F. arisanus were generated under laboratory conditions at six constant temperatures (15, 20, 25, 30, 28 and 35 °C; 75% RH, L12:D12 photoperiod) and under variable conditions in a screenhouse on B. dorsalis. Several non-linear functions were fitted to model species development, mortality, longevity and oviposition using the Insect Life Cycle Modeling (ILCYM) software. The established phenology models were stochastically simulated at variable temperatures to estimate the life table parameters. Fopius arisanus completed development from egg to adult at all the temperatures tested except at 35 °C. Mean developmental time from egg to adult was inversely proportional to the temperature. The minimum temperature threshold (Tmin) from egg to adult was 8.15 °C, while the maximum temperature threshold (Tmax) was estimated at 34.2 °C. The optimal temperature for immature stages survival was predicted for 20-30 °C. The optimum fecundity estimated was 251 eggs/female at 22 °C. Following the stochastic simulations under natural conditions of the selected agro-ecological zones, it appears that the Humid Forest with Bimodal Rainfall provides a suitable thermal condition for potential population growth of F. arisanus. The present study shows the importance of temperature on the demographic parameters of F. arisanus. Implications of present findings on the biological control of B. dorsalis under climate change scenarios is discussed.

Effect of fruit and host fly species on the associative learning by Fopius arisanus.

Parasitoids, released in augmentative biological control programmes, which display a rapid host-location capacity, have a higher likelihood of successfully controlling target pest species. By learning to associate sensory cues to a suitable oviposition site, might parasitoids used as biological control agents, locate hosts more rapidly, and perhaps increase the efficacity of e.g. Tephritidae fruit fly management. We studied associative learning of Fopius arisanus (Hymenoptera: Braconidae) and tested its range of learning in natural and conditional hosts and host fruits, i.e. Bactrocera dorsalis, Zeugodacus cucurbitae, Ceratitis capitata and Ceratitis cosyra (Diptera: Tephritidae) and on fruits (papaya, tomato, banana). Naïve female F. arisanus were compared with experienced wasps, which had been offered infested and non-infested fruit, and been allowed to oviposit. Preferences for olfactory cues from infested fruits were thereafter assessed in a two-choice olfactometer. Naïve and trained parasitoids preference differed in general and non-responders to infested fruits were higher among naïve parasitoids. The trained wasps preferred the fruit infested in the training more than the control fruit, for all combination, except when C. cosyra infested the fruits, hence avoidance behavioural response was observed towards the odour of the infested fruit. Fopius arisanus was capable of behaviourally respond to the learned information, e.g. associative odour learning was achieved, yet limited depending on interaction level, fruit fly and fruit combination. To create F. arisanus preference of an associated odour, it might hence be needed to ensure oviposition in perceived suitable host and host fruit, for the parasitoid learning to become favourable in a biological control setup.

Fruit Preference, Parasitism, and Offspring Fitness of Fopius arisanus (Hymenoptera: Braconidae) Exposed to Bactrocera dorsalis' (Diptera: Tephritidae) Infested Fruit Species.

Fopius arisanus (Sonan) (Hymenoptera: Braconidae) is a koinobiont solitary parasitoid of various fruit flies, particularly those in the genus Bactrocera. Researchers introduced F. arisanus into Africa for the biological control of Bactrocera dorsalis (Hendel) (Diptera: Tephritidae), a pest of a wide range of fruit trees and vegetables. However, the suitability of host fruit species as egg-laying substrates for parasitoid development remains poorly investigated in tropical Africa. The present study examines the preference and performance of F. arisanus on B. dorsalis reared on eleven fruit species through laboratory choice-test trials. We assessed the oviposition activity, parasitism rate, developmental time, and offspring fitness of F. arisanus on nine cultivated and two wild host fruits species. Oviposition attempts were higher on Psidium guajava (L.) (Myrtales: Myrtaceae) and Mangifera indica (L.) (Sapindales: Anacardiaceae) than on the other host fruits tested. The wasp parasitized host eggs in P. guajava in no-choice experiments. Psidium guajava, Irvingia wombulu (Vermoesen) (Malpighiales: Irvingiaceae), and Irvingia gabonensis (Aubry_Lecomte) Baill (Malpighiales: Irvingiaceae) were suitable for parasitism in choice tests. Of all host fruits tested, the body and hind tibia lengths of both parasitoid sexes emerging from M. indica were longer than on the others. The female ovipositor was long on Annona squamosa (L.) (Magnoliales: annonaceae) and short on Eribotrya japonica ([Thunb.] Lindl.; Rosales: Rosaceae). We obtained the longest preimaginal developmental time for both sexes on E. japonica and the shortest for females and males on Carica papaya (L.) (Brassicales: Caricaceae). These results demonstrate the ability of some tested fruit species to serve for the permanent establishment of F. arisanus in the field.