Ivan Rwomushana

Field infestation, life history and demographic parameters of the fruit fly Bactrocera invadens (Diptera: Tephritidae) in Africa

Field infestation rates of an invasive fruit fly species, Bactrocera invadens Drew Tsuruta & White on mango was determined at different localities in Kenya. At most of the locations and especially at low elevations, B. invadens frequently shared the same fruit with the indigenous fruit fly species Ceratitis cosyra (Walker) but often occurred at higher numbers than C. cosyra. The level of infestation varied with location ranging from 3.0 to 97.2 flies per kg of fruit. There was a significant inverse relationship between numbers of flies per kg of fruit and elevation at which fruit was collected, suggesting that B. invadens is a predominantly lowland pest. On an artificial diet, development of B. invadens immatures lasted 25 days; egg incubation required 1.2 days, larval development 11.1 days and puparia-adult development 12.4 days. About 55% of eggs developed to the adult stage. Life expectancy at pupal eclosion was 75.1 days in females and 86.4 days in males. Average net fecundity and net fertility were 794.6 and 608.1 eggs, respectively, while average daily oviposition was 18.2 eggs. Daily population increase was 11% and mean generation time was 31 days. Results are discussed in relation to the biology and ecology of the insect and in the development of mass rearing and control measures for B. invadens.

Evidence for Competitive Displacement of Ceratitis cosyra by the Invasive Fruit Fly Bactrocera invadens (Diptera: Tephritidae) on Mango and Mechanisms Contributing to the Displacement

ABSTRACT Bactrocera invadens Drew, Tsuruta & White (Diptera: Tephritidae) invaded Kenya in 2003. Before the arrival of B. invadens, the indigenous fruit fly species Ceratitis cosyra (Walker) was the predominant fruit fly pest of mango (Mangifera indica L.). Within 4 yr of invasion, B. invadens has displaced C. cosyra and has become the predominant fruit fly pest of mango, constituting 98 and 88% of the total population in traps and mango fruit at Nguruman, respectively. We tested two possible mechanisms responsible for the displacement namely; resource competition by larvae within mango fruit and aggression between adult flies. Under interspecific competition, larval duration in B. invadens was significantly shorter (6.2 ± 0.6-7.3 ± 0.3 d) compared with C. cosyra (8.0 ± 1.2-9.4 ± 0.4 d). Pupal mass in C. cosyra was affected by competition and was significantly reduced (7.4 ± 0.3-9.6 ± 0.6 mg) under competitive interaction compared with the controls (12.1 ± 1.5-12.8 ± 1.1 mg). Interspecific competition also had a significant adverse effect on C. cosyra eclosion, with fewer adults emerging under co-infestation compared with the controls. Interference competition through aggressive behavior showed that fewer C. cosyra (3.1 ± 0.8) landed on mango dome compared with the controls (14.2 ± 1.5) when adults were mixed with B. invadens adults in Plexiglas cages. Similarly the number of times C. cosyra was observed ovipositing was significantly lower (0.2 ± 0.2) under competitive interaction compared with the controls (6.1 ± 1.8). Aggressive encounters in the form of lunging/head-butting and chasing off other species from the mango dome was higher for B. invadens compared with C. cosyra. Our results suggest that exploitative competition through larval scrambling for resources and interference competition through aggressive behaviors of the invader are important mechanisms contributing to the displacement of C. cosyra by B. invadens in mango agroecosystems.

Fruit Fly (Diptera: Tephritidae) Host Status and Relative Infestation of Selected Mango Cultivars in Three Agro Ecological Zones in Uganda

ABSTRACT Despite their economic importance, there is paucity of knowledge on fruit fly host status in Uganda. Therefore, this study set out to profile the host range of the main fruit fly pests and determine the susceptibility of selected fruits and mango cultivars across three main mango agro ecological zones, which included: Western Medium High Altitude Farmlands (WMHF), Lake Victoria Crescent (LVC), and the Northern Moist Farmlands (NMF) in Uganda. A wide range of fruits was sampled across the three zones. These were incubated at the National Agricultural Research Laboratories following standard protocols. Emerging fruit fly species were identified using standard keys and counted. Among the sampled fruits, 633 (35.0%) individual fruits from 15 plant families were positive for fruit fly infestation. Bactrocera invadens dominated (76.3%) of the positive samples, while infestation by native species, such as Ceratitis capitata and Ceratitis cosyra, was negligible. Annonaceae, Solanaceae, Rutaceae, and Anacardiaceae plant families recorded significantly more host species, while the number of pest fruit flies (species richness) per plant species followed a similar trend: Solanaceae > Rutaceae > Anacardiaceae. There was significant (P < 0.0001) variability in infestation among mango fruit cultivars, both within and across zones. When all zones were pooled together, Tommy Atkins and Kent, and Keitt, Kate, and Biire were the least and most infested, respectively. In conclusion, fruit flies have a diverse range of commercial and non-commercial hosts in Uganda. Strategies for fruit fly pest eradication in the country should ensure elimination or management of alternative fruit hosts and integration of tolerant mango cultivars in fruit development programs.

DNA Barcode Reference Library for the African Citrus Triozid, Trioza erytreae (Hemiptera: Triozidae): Vector of African Citrus Greening

Abstract Citrus (Citrus spp.) production continues to decline in East Africa, particularly in Kenya andTanzania, the two major producers in the region. This decline is attributed to pests and diseases including infestation by the African citrus triozid, Trioza erytreae (Del Guercio) (Hemiptera:Triozidae). Besides direct feeding damage by adults and immature stages, T. erytreae is the main vector of ‘Candidatus Liberibacter africanus’, the causative agent of Greening disease in Africa, closely related to Huanglongbing. This study aimed to generate a novel barcode reference library for T. erytreae in order to use DNA barcoding as a rapid tool for accurate identification of the pest to aid phytosanitary measures. Triozid samples were collected from citrus orchards in Kenya, Tanzania, and South Africa and from alternative host plants. Sequences generated from populations in the study showed very low variability within acceptable ranges of species. All samples analyzed were linked to T. erytreae of GenBank accession number KU517195. Phylogeny of samples in this study and other Trioza reference species was inferred using the Maximum Likelihood method. The phylogenetic tree was paraphyletic with two distinct branches. The first branch had two clusters: 1) cluster of all populations analyzed with GenBank accession of T. erytreae and 2) cluster of all the other GenBank accession of Trioza species analyzed except T. incrustata Percy, 2016 (KT588307.1), T. eugeniae Froggatt (KY294637.1), and T. grallata Percy, 2016 (KT588308.1) that occupied the second branch as outgroups forming sister clade relationships.These results were further substantiated with genetic distance values and principal component analyses.

Fruit Fly Species Composition, Distribution and Host Plants with Emphasis on Mango-Infesting Species

Mango is the most widely cultivated fruit tree in tropical and sub-tropical Africa. However, the sustainability of this lucrative business is threatened by infestations of fruit flies (Diptera: Tephritidae) that annually inflict heavy economic losses on the industry. The nutritional quality of different fruit species can influence the survival and fecundity of adult fruit flies. This host-insect interaction determines the species composition, distribution and abundance of the major frugivorous tephritids. The economic impact of fruit fly pest species includes direct yield losses and the loss of export markets due to quarantine restrictions implemented to prevent the entry and establishment of exotic fruit fly species in importing countries. The economically important tephritid fruit flies attacking mango in Africa can be divided into two major categories based primarily on their origin, i.e., invasive (Bactrocera dorsalis, Bactrocera zonata and Zeugodacus cucurbitae) and indigenous species (Ceratitis anonae, Ceratitis capitata, Ceratitis catoirii, Ceratitis cosyra, Ceratitis ditissima, Ceratitis fasciventris, Ceratitis quinaria, Ceratitis rosa [recent taxonomic advances have separated C. rosa into two species; C. rosa and C. quilicii], Ceratitis silvestrii, Dacus ciliatus and some unverified records of Ceratitis punctata and Dacus bivittatus). These species are known to have a wide host range and distribution across Africa. Their distribution is also influenced by competitive interactions between native and indigenous species. The host plant status and distribution of fruit fly species is an evolving phenomenon largely due to new invasions, misidentification and identification of hitherto unknown species. For this reason this review provides the current situation but should be updated on a regular basis.

Integrated Management of Fruit Flies – Case Studies from Uganda

Fruit flies (Diptera: Tephritidae) pose a threat to commercialisation of the horticulture industry in Uganda. They impair the quality and quantity of fruits produced, and limit access to lucrative regional and global markets. Here we explore past and present efforts, and future plans for research and management, of fruit flies in Uganda. Early research geared towards collection and identification of fruit flies recognised the pest status of many species and highlighted the need for establishing sustainable management strategies. Subsequently large-scale research initiatives have substantially increased knowledge on the biology and ecology of fruit flies in Uganda. Based on these studies, integrated pest management (IPM) options for fruit flies have been designed and piloted. Amongst the most promising options are the Male Annihilation Technique (MAT) in combination with the Bait Annihilation Technique (BAT) or Protein Food Bait (PFB) and Orchard Sanitation (OS). Fruit bagging is also receiving attention. It is now recommended that IPM options are combined and scaled up in an area-wide approach. The government of Uganda has demonstrated genuine commitment to eradication of fruit flies through three key project initiatives: (i) Gaining insight into the ecological and physiological factors influencing fruit fly populations and infestation rates in mango-growing regions of Uganda (NARO-MSI); (ii) Equipping key technical personnel at local and district levels with knowledge on identification and management of key fruit fly pest species (NAADS); (iii) Promotion and adoption of IPM practices for fruit fly management (NARO-ATAAS). These initiatives will ensure the long-term sustainability of management options.

Acceptability and suitability of Spodoptera exigua (Hübner) for Cotesia icipe Fernandez-Triana & Fiaboe on amaranth

The beet armyworm Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae) is a polyphagous insect that is distributed worldwide and was recently reported as an important pest on African indigenous vegetables. Cotesia icipe Fernandez‐Triana & Fiaboe (Hymenoptera: Braconidae) is a recently described parasitoid, reported from various Afrotropical countries. This work investigated the performance of C. icipe on S. exigua infesting Amaranthus dubius Mart. ex Thell. under laboratory conditions. Cotesia icipe was aggressive on the host and successfully oviposited on S. exigua with 70% of parasitoid females ovipositing after 2 hr of exposure. Parasitoid densities significantly affected the parasitism rate and the nonreproductive larval mortality. Parasitism rate was 9.7 ± 0.8% and 59.5 ± 3.1% for a single and cohort of five females released, respectively, when offered 50 host larvae. The cohort female release resulted in significantly higher larval nonreproductive mortality than the single release. However, there was no significant difference between parasitoid release densities in regard to pupal nonreproductive mortality. The larval and pupal mortalities in the presence of C. icipe were significantly higher than the natural mortalities at both parasitoid release densities. The parasitoid sex ratio was female‐biased for the cohort females but balanced when a single female was released. The hind tibia and forewing lengths were not affected by the density of female parasitoids but there were variations according to sex. The implication of these findings on the potential use of C. icipe for biological control of S. exigua in amaranth production systems is discussed.

Performance of the newly identified endoparasitoid Cotesia icipe Fernandez-Triana & Fiaboe on Spodoptera littoralis (Boisduval)

Cotesia icipe Fernandez‐Triana & Fiaboe is a solitary koinobiont larval endoparasitoid, recently discovered in Kenya and new to science, that parasitizes select lepidopteran herbivores of amaranth. We investigated its host range on five commonly encountered amaranth lepidopteran defoliators. Cotesia icipe accepted, successfully and aggressively parasitized the amaranth noctuid defoliators Spodoptera littoralis (Boisduval) and Spodoptera exigua (Hübner), but failed to parasitize Herpetogramma bipunctalis (F.), Spoladea recurvalis (F.) and Udea ferrugalis (Hübner) all in Crambidae family. On S. littoralis, C. icipe was highly efficient, with 95% of females successfully ovipositing during 2 hr of exposure. Parasitism rate and larval and pupal non‐reproductive mortalities were significantly higher at higher parasitoid density. A single female of C. icipe parasitized 42.99 ± 2.66% of the 50 exposed larvae for oviposition in 24 hr, whereas a cohort of five females of C. icipe conferred 85.59 ± 1.46% parasitism rate. The efficiency ratio per female was much higher in single releases than in cohort releases while a balanced sex ratio was obtained in F1 offspring regardless of the density of female released. The potential use of C. icipe for conservation and augmentative biological control of S. littoralis in amaranth as well as its potential use against other Noctuid moths and in other commodities is discussed.

Projections of climate-induced future range shifts among fruit fly (Diptera: Tephritidae) species in Uganda

Masembe C., Isabirye B.E., Rwomushana I., Nankinga C.K., Akol A.M. (2016): Projections of climate-induced future range shifts among fruit fly (Diptera: Tephritidae) species in Uganda. Plant Protect. Sci., 52: 26–34. The potential impact of future climate change on fruit fly species distribution was assessed in Uganda using two general circulation models (HADCM and CCCMA) and two future predicted CO2 emission scenarios (A2 and B2), under both full and no species dispersal modes. Future ranges were overall projected to decline by 25.4% by year 2050. Under full-dispersal, D. ciliatus > C. cosyra > b. invadens ranges were predicted to increase, while the rest are likely to decrease. In the no-dispersal scenario, a significant average decrease in size of niches is predicted. Range losses are predicted higher under B2 than A2. Future niches will likely shift to northern Uganda. The results should assist in the development of climate change adaptive pest management strategies.