Daisy Salifu

Taxonomic Identity of the Invasive Fruit Fly Pest, Bactrocera invadens: Concordance in Morphometry and DNA Barcoding

In 2003, a new fruit fly pest species was recorded for the first time in Kenya and has subsequently been found in 28 countries across tropical Africa. The insect was described as Bactrocera invadens, due to its rapid invasion of the African continent. In this study, the morphometry and DNA Barcoding of different populations of B. invadens distributed across the species range of tropical Africa and a sample from the pests putative aboriginal home of Sri Lanka was investigated. Morphometry using wing veins and tibia length was used to separate B. invadens populations from other closely related Bactrocera species. The Principal component analysis yielded 15 components which correspond to the 15 morphometric measurements. The first two principal axes contributed to 90.7% of the total variance and showed partial separation of these populations. Canonical discriminant analysis indicated that only the first five canonical variates were statistically significant. The first two canonical variates contributed a total of 80.9% of the total variance clustering B. invadens with other members of the B. dorsalis complex while distinctly separating B. correcta, B. cucurbitae, B. oleae and B. zonata. The largest Mahalanobis squared distance (D2 = 122.9) was found to be between B. cucurbitae and B. zonata, while the lowest was observed between B. invadens populations against B. kandiensis (8.1) and against B. dorsalis s.s (11.4). Evolutionary history inferred by the Neighbor-Joining method clustered the Bactrocera species populations into four clusters. First cluster consisted of the B. dorsalis complex (B. invadens, B. kandiensis and B. dorsalis s. s.), branching from the same node while the second group was paraphyletic clades of B. correcta and B. zonata. The last two are monophyletic clades, consisting of B. cucurbitae and B. oleae, respectively. Principal component analysis using the genetic distances confirmed the clustering inferred by the NJ tree.

Differential Effects of Pesticide Applications on Liriomyza huidobrensis (Diptera: Agromyzidae) and its Parasitoids on Pea in Central Kenya

ABSTRACT Three Liriomyza species [Liriomyza huidobrensis (Blanchard), Liriomyza trifolii (Burgess), and Liriomyza sativae Blanchard] have been reported as the most important leafminer pests in vegetable production systems in Africa. In Kenya, farmers rely on indiscriminate synthetic insecticides use. On-farm field investigations were set up at three different locations (Sagana, Kabaru, and Naromoru) in central Kenya to determine the effect of pesticide application on the abundance of leafminers and their parasitoids under three management practices, namely: farmer practice (FP), reduced pesticide use (RP), and a control with no use of pesticides (CO). In addition, laboratory experiments were designed to test the effect of commonly used pesticides in pea production systems in central Kenya——Dimethoate, Dynamec, Thunder, Cyclone, Bestox, Folicur, Milraz, and Bulldock——on L. huidobrensis and two of its parasitoids, Diglyphus isaeaWalker and Phaedrotoma scabriventris Nixon. The mean numbers of leafminer flies in control treatment were higher than in RP and FP in both first and second seasons across all sites, but RP and FP did not differ significantly. Parasitoid numbers were very low and there was no much variation between treatments at each location in both first and second seasons. No significant differences were observed between the three management practices with regards to the yield measurements. In the laboratory, the estimated LD50 values for L. huidobrensis larvae were all more than two times higher than the recommended dosages, while the LD50 of adults were below the recommended dosages. The estimated LD50 values for the parasitoids were much lower than recommended dosages for all pesticides except Thunder. This study, therefore, demonstrates that the pesticides currently used do not control the Liriomyza leafminer larvae that constitute the most destructive stage of the pest, but are rather detrimental to their parasitoids. In addition, the current low level of parasitoids recorded under field conditions even where no pesticide was used during this study, warrants consideration of classical biological control programs.

Effect of temperature on immature development and longevity of two introduced opiine parasitoids on Bactrocera invadens

Temperature‐dependent development, parasitism and longevity of the braconid parasitoids, Fopius arisanus Sonan and Diachasmimorpha longicaudata Ashmed on Bactorcera invadens Drew Tsuruta & White, was evaluated across five constant temperatures (15, 20, 25, 30 and 35°C). Developmental rate decreased linearly with increasing temperature for both the parasitoid species. Linear and Brière‐2 nonlinear models were used to determine the lower temperature threshold at which the developmental rate (1/D) approached zero. For F. arisanus, lower thresholds to complete development estimated with the linear and nonlinear models were 10.1 and 6.9°C, respectively. The total degree‐days (DD) required to complete the development estimated by the linear model for F. arisanus was 360. In D. longicaudata, the linear and nonlinear models estimated lower thresholds of 10.4 and 7.3°C, respectively, and the total DD estimated was 282. In F. arisanus, percentage parasitism differed significantly across all temperatures tested and was highest at 25°C (71.1 ± 2.5) and lowest at 15°C (46.4 ± 1.4). Parasitoid progeny sex ratio was female biased at all temperatures except at 20°C. In D. longicaudata, percentage parasitism was highest at 20°C (52.2 ± 4.0) and lowest at 15°C (27.7 ± 2.5). Parasitoid progeny sex ratio was female biased and similar for all temperatures. Adult longevity of both parasitoids was shortest at 35°C and longest at 15°C, and females lived significantly longer than males at all temperatures tested. Our findings provide some guidance for future mass rearing and field releases of the two parasitoids for the management of B. invadens in Africa.

Host plant-related parasitism and host feeding activities of Diglyphus isaea (Hymenoptera: Eulophidae) on Liriomyza huidobrensis, Liriomyza sativae, and Liriomyza trifolii (Diptera: Agromyzidae).

ABSTRACT Host plant species can affect the behavior and attributes of parasitoids, such as host searching, oviposition, and offspring fitness. In this study, parasitism, host feeding, and sex ratios of Diglyphus isaea (Walker) (Hymenoptera: Eulophidae) on Liriomyza huidobrensis (Blanchard), Liriomyza sativae Blanchard, and Liriomyza trifolii (Burgess) (Diptera: Agromyzidae) larvae reared on Phaseolus vulgaris L., Pisum sativum L., Solanum lycopersicum L., and Vicia faba L. were determined. In no-choice tests, L. huidobrensis had the highest rate of parasitism when reared on P. vulgaris (46%), L. sativae when reared on V. faba (59%) and P. vulgaris (59%), and L. trifolii when reared on S. lycopersicum (68%). Host feeding in no-choice tests ranged between 2% and 36% and was highest on L. trifolii reared on V. faba. Results of choice tests showed a significant interaction effect for host plant and Liriomyza species on parasitism and host feeding. Within plant mixtures, L. sativae reared on P. vulgaris had the highest rate of parasitism (31%), followed by L. trifolii on S. lycopersicum (29%) and L. huidobrensis on V. faba (28%). Host feeding was highest on L. trifolii reared on S. lycopersicum (14%) and lowest on L. huidobrensis reared on P. sativum and S. lycopersicum (1%). In some instances, plant mixtures resulted in a higher proportion of females of D. isaea than single plant species. The highest proportion of females was obtained in plant mixtures on L. huidobrensis and L. trifolii on V. faba (71 and 72%, respectively). This study suggests that planting crop mixtures can potentially lead to higher proportions of females, thus improving parasitism and host feeding, depending on Liriomyza and host plant species.

Differential effects of various African nightshade species on the fecundity and movement of Tetranychus evansi (Acari: Tetranychidae)

The tomato red spider mite Tetranychus evansi Baker & Pritchard is a serious pest of solanaceous plants worldwide. Management of this oligophagous pest in African nightshades has been a challenge to smallholder African farmers due to its high reproductive rate and rapid development of resistance to synthetic pesticides. The aim of the present study was to determine the influence of leaf trichomes on T. evansi by comparing its fecundity and movement on the leaf surfaces of five African nightshade species, namely Solanum sarrachoides Sendter, S. villosum Miller, S. tarderemotum Bitter, S. americanum Miller and S. scabrum Miller. Data were recorded in the laboratory at 23 ± 1°C, 50–70% relative humidity and a 12 h light:12 h dark photoperiod for the effect of trichome type and density of the abaxial leaf surface on mite fecundity. Distances travelled by mites on the leaf surface from the edge of a thumbtack pin inserted on the leaf were also recorded. Different trichomes, glandular and non-glandular types, were identified. There was a significant negative correlation of fecundity and distance walked by mites with the density of glandular trichomes. Significantly fewer eggs were laid on S. sarrachoides in comparison with the other Solanum species. The distance walked by mites was also significantly shorter in this species, indicating that higher densities of glandular trichomes interfere with mite movements. These results suggest that African nightshade genotypes differ in their levels of resistance to T. evansi, which is partially associated with differences in trichome types and their densities.

Composition and Genetic Diversity of Mosquitoes (Diptera: Culicidae) on Islands and Mainland Shores of Kenya's Lakes Victoria and Baringo.

Abstract The Lake Baringo and Lake Victoria regions of Kenya are associated with high seroprevalence of mosquito-transmitted arboviruses. However, molecular identification of potential mosquito vector species, including morphologically identified ones, remains scarce. To estimate the diversity, abundance, and distribution of mosquito vectors on the mainland shores and adjacent inhabited islands in these regions, we collected and morphologically identified adult and immature mosquitoes and obtained the corresponding sequence variation at cytochrome c oxidase 1 (COI) and internal transcribed spacer region 2 (ITS2) gene regions. A total of 63 species (including five subspecies) were collected from both study areas, 47 of which have previously been implicated as disease vectors. Fourteen species were found only on island sites, which are rarely included in mosquito diversity surveys. We collected more mosquitoes, yet with lower species composition, at Lake Baringo (40,229 mosquitoes, 32 species) than at Lake Victoria (22,393 mosquitoes, 54 species). Phylogenetic analysis of COI gene sequences revealed Culex perexiguus and Cx. tenagius that could not be distinguished morphologically. Most Culex species clustered into a heterogeneous clade with closely related sequences, while Culex pipiens clustered into two distinct COI and ITS2 clades. These data suggest limitations in current morphological identification keys. This is the first DNA barcode report of Kenyan mosquitoes. To improve mosquito species identification, morphological identifications should be supported by their molecular data, while diversity surveys should target both adults and immatures. The diversity of native mosquito disease vectors identified in this study impacts disease transmission risks to humans and livestock.

Identification of stingless bees (Hymenoptera: Apidae) in Kenya using morphometrics and DNA barcoding

Stingless bees are important pollinators of wild plants and crops. The identity of stingless bee species in Africa has not been fully documented. The present study explored the utility of morphometrics and DNA barcoding for identification of African stingless bee populations, and to further employ these tools to identify potential cryptic variation within species. Stingless bee samples were collected from three ecological zones, namely Kakamega Forest, Mwingi and Arabuko-Sokoke Forest, which are geographically distant and cover high, medium and low altitudes, respectively. Forewing and hind leg morphometric characters were measured to determine the extent of morphological variation between the populations. DNA barcodes were generated from the mitochondrial cytochrome c-oxidase I (COI) gene. Principal Component Analysis (PCA) on the morphometric measurements separated the bee samples into three clusters: (1) Meliponula bocandei; (2) Meliponula lendliana + Plebeina hildebrandti; (3) Dactylurina schmidti + Meliponula ferruginea black + Meliponula ferruginea reddish brown, but Canonical Variate Analysis (CVA) separated all the species except the two morphospecies (M. ferruginea reddish brown and black). The analysis of the COI sequences showed that DNA barcoding can be used to identify all the species studied and revealed remarkable genetic distance (7.3%) between the two M. ferruginea morphs. This is the first genetic evidence that M. ferruginea black and M. ferruginea reddish brown are separate species.

Opposing Roles of Foliar and Glandular Trichome Volatile Components in Cultivated Nightshade Interaction with a Specialist Herbivore

Plant chemistry is an important contributor to the interaction with herbivores. Here, we report on a previously unknown role for foliar and glandular trichome volatiles in their interaction with the specialist herbivore of solanaceous plants, the tomato red spider mite Tetranychus evansi. We used various bioassays and chemical analyses including coupled gas chromatography-mass spectrometry (GC/MS) and liquid chromatography coupled to quadrupole time of flight mass spectrometry (LC-QToF-MS) to investigate this interaction between cultivated African nightshades and T. evansi. We show that, whereas morphologically different cultivated African nightshade species released similar foliar volatile organic compounds (VOCs) that attracted T. evansi, VOCs released from exudates of ruptured glandular trichomes of one nightshade species influenced local defense on the leaf surface. VOCs from ruptured glandular trichomes comprising mainly saturated and unsaturated fatty acids deterred T. evansi oviposition. Of the fatty acids, the unsaturated fatty acids accounted for >40% of the oviposition deterrent activity. Our findings point to a defense strategy in a plant, based on opposing roles for volatiles released by foliar and glandular trichomes in response to attack by a specialist herbivore.

Effect of larval age and supplemental feeding on morphometrics and oviposition in honey bee Apis mellifera scutellata queens

Although the effects of numerous factors (such as age of grafted larvae, supplemental feeding and mating) have been studied on the honey bees of Europe and America, they remain unknown for African bee races. To bridge this gap, a study was undertaken at the icipe Karura forest apiaries in Kenya to determine the effect of larval age and supplemental feeding on morphometrics and oviposition in the honey bee Apis mellifera scutellata queens. Queens were reared in 12 colonies with two feeding regimes, fed and not fed. Five larval age groups: 6, 12, 24, 36, and 48 h old, were grafted from each colony. We measured the fresh weight, spermatheca volume and the external parameters of the emerged queens and compared the oviposition rate by counting the number of eggs laid daily in naturally mated queens (NM) and artificially inseminated queens (AI). Our results show that age of grafted larvae and supplemental feeding significantly affect the morphometrics of the reared queens (p = 0.001), while oviposition rate is more or less the same in NM and AI. This work could eventually be used to select the best breed of honey bee subspecies in East Africa and improve queen rearing methods.

Behavioral responses of the small hive beetle, Aethina tumida, to odors of three meliponine bee species and honey bees, Apis mellifera scutellata

Recent studies have shown that honey bees, bumble bees, and some meliponine bee species of the genera Trigona, Meliponula, and Dactylurina are hosts of the small hive beetle (SHB) Aethina tumidaMurray (Coleoptera: Nitidulidae), a pest of honey bee colonies in various regions of the world. Olfaction has been implicated in SHB infestations of honey bee and bumble bee colonies. We used olfactometer bioassays to investigate responses of adult male and female SHBs to odors from intact colonies and separate hive components (pot honey, pot pollen, cerumen, and propolis) of three African meliponine bee species, Meliponula ferruginea (Lepeletier) (black morphospecies), M. ferruginea (reddish brown morphospecies), and Meliponula bocandei (Spinola) (Hymenoptera: Apidae). Although both sexes of the beetle strongly preferred intact colony, pot honey, and pot pollen odors, there was no evidence of attraction to propolis and cerumen odors from the three meliponine bee species. Both sexes of SHB also strongly preferred odors from honey bees, Apis mellifera L. (Hymenoptera: Apidae), over odors from the three meliponine bee species. Our results provide substantial evidence of the host potential of African meliponine bees for the SHB, and we discuss this complex association of the SHB with species within the Apidae family.