Komivi Senyo Akutse

Species Composition, Distribution, and Seasonal Abundance of Liriomyza Leafminers (Diptera: Agromyzidae) Under Different Vegetable Production Systems and Agroecological Zones in Kenya

ABSTRACT A longitudinal study to identify the species of Liriomyza leafminer, their distribution, relative abundance, and seasonal variation, including their host range, was conducted in vegetable fields at three altitudes in Kenya from November 2011 to November 2012. Three main species were identified: Liriomyza huidobrensis (Blanchard), Liriomyza sativae Blanchard, and Liriomyza trifolii (Burgess), of which L. huidobrensis was the most abundant across all altitudes irrespective of the cropping season and accounting for over 90% of the total Liriomyza specimens collected. Liriomyza species were collected from all infested incubated leaves of 20 crops surveyed belonging to seven families: Fabaceae, Solanaceae, Cucurbitaceae, Malvaceae, Brassicaceae, Amaranthaceae, and Amaryllidaceae. However, more than 87.5% of the Liriomyza species were obtained from only four of these crops: Pisum sativum L., Phaseolus vulgaris L., Solanum lycopersicum L., and Solanum tuberosum, thereby demonstrating that Fabaceae and Solonaceae crops are the most important hosts with regard to Liriomyza species richness and relative abundance. L. huidobrensis had the widest host range (20 crops), followed by L. sativae (18 crops) and L. trifolii (12 crops). Although L. trifolii has been considered the dominant Liriomyza leafminer in Kenya, this study suggests that this may not be the case anymore, as L. huidobrensis dominates at all altitudes.

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.

Prospects of fungal endophytes in the control of Liriomyza leafminer flies in common bean Phaseolus vulgaris under field conditions

Field trials were carried out for two seasons in two sites (Sagana and Naromoru, Central province of Kenya) to evaluate the prospects of endophyte isolates of Beauveria bassiana (Balsamo) Vuillemin G1LU3 and Hypocrea lixii Patouillard F3ST1 for the control of Liriomyza leafminer in common bean Phaseolus vulgaris L. crops through seeds inoculation. Autodissemination device (AD) treated with conidia of Metarhizium anisopliae (Metschnikoff) Sorokin ICIPE 20 was also added as a treatment. Leafminer infestation was not significantly different during the first season but was higher in the controls than in endophtyte treatments at both sites during the second season. Three key Liriomyza species [(L. huidobrensis Blanchard, L. sativae Blanchard and L. trifolii (Burgess)] and six parasitoid species [(Opius dissitus Muesebeck, Phaedrotoma scabriventris Nixon, Diglyphus isaea Walker, Neochrysocharis formosa Westwood, Hemiptarsenus varicornis Girault and Halticoptera arduine (Walker)] were identified during the trials. Leafminer infestation, number of pupae, leafminer flies and parasitoids emergence and yield were the parameters evaluated. Both isolates successfully colonized different parts of P. vulgaris plants, although the colonization was higher with H. lixii F3ST1 than B. bassiana G1LU3 at both sites. The mean number of pupae from the infested leaves varied between 141–252 and 331–416 in endophyte and control treatments, respectively, during the first season and from 110–223 to 366–523, respectively, in endophyte and control treatments during the second season. There were no significant differences among the treatments in the number of parasitoids that emerged from pupae. Higher yield of P. vulgaris seeds was obtained in endophyte than in control treatments. The inclusion of AD treatment did not have significant effect on all the parameters evaluated, except yield. Results of the present study suggest that both fungal isolates hold potential for pest management and could be considered for the control of leafminer flies. However, there is the need to confirm these results on large-scale trials.

Liriomyza Leafminer (Diptera: Agromyzidae) Parasitoid Complex in Different Agroecological Zones, Seasons, and Host Plants in Kenya

Abstract Liriomyza leafminers (Diptera: Agromyzidae) are severe pests of vegetables and ornamentals worldwide. Previous studies revealed low leafminer parasitism across different agroecological zones in Kenya. The present paper reports on the composition of leafminer parasitoids at different elevations, in different seasons, and on different host crops. Surveys were conducted monthly from January to November 2012, and nine parasitoid species were recovered. Total mean parasitism in the study sites was 31.23 ± 1.03% from a total of 20 different vegetable Liriomyza-infested crops belonging to seven families. Diglyphus isaea (Walker) (Hymenoptera: Eulophidae), Phaedrotoma scabriventris, a newly released parasitoid, and Opius dissitus Muesebeck (Hymenoptera: Braconidae) were the most abundant at all elevations, accounting for 67.3, 18.6, and 9.2% of total parasitoids, respectively. Elevation, season, and host crop significantly affected the parasitoid species present and their abundance. Diglyphus isaea was more abundant at the high- and mid-elevations at all seasons compared with the low-elevation, whereas the lower-elevation favored higher abundance of P. scabriventris and O. dissitus during the long rainy season compared with the high- and mid-elevations at all seasons. Of all the host crops surveyed, parasitoids were more abundant on tomato, local kidney bean, snow pea and French bean than other crops. The total parasitism rate observed in this study suggests a considerable improvement in leafminer parasitism compared with previous surveys in Kenya. The implications of these findings for leafminer management in vegetable and ornamental production in Kenya are discussed.

Interaction between Phaedrotoma scabriventris Nixon and Opius dissitus Muesebeck (Hymenoptera: Braconidae): Endoparasitoids of Liriomyza Leafminer

The exotic parasitoid, Phaedrotoma scabriventris Nixon, was imported from Peru for the biological control of invasive Liriomyza species in vegetable and ornamental crops in Kenya where Opius dissitus Muesebeck is the most abundant indigenous Liriomyza parasitoid. Both species are solitary larva-pupal endoparasioids attacking the same larval stage. In order to assess whether these two species compete or co-exist, an interaction study involving sole, sequential and simultaneous releases of the two species on polyphagous Liriomyza huidobrensis (Blanchard) was conducted in the laboratory at the International Centre of Insect Physiology and Ecology (ICIPE), Nairobi, Kenya. Simultaneous releases of 50 individuals each of the two parasitoids resulted in significantly higher total parasitism rate (61.96±4.60) than in the single release of P. scabriventris (34.94±8.50). Simultaneous release of 25 individuals of each species resulted in a parasitism rate (44.52 ± 2.75) similar to that obtained for single releases of 50 individuals of O. dissitus (42.57 ± 3.35) and P. scabriventris (34.94 ± 8.50). No significant effect was observed in total parasitism between sequential and single releases of 50 individuals of each species. The specific parasitism rate of each parasitoid species in the simultaneous release of 50 individuals of each species was not significantly different from when each species was released alone. The first introduced parasitoid in sequential releases achieved the same parasitism rate as when released alone. However, the second released species gave a significantly lower parasitism rate than when released alone and compared to the first released species. The F1 progeny sex ratio was balanced for P. scabriventris but male-biased inO. dissitus. The sex ratios of both parasitoid species were not significantly affected, neither in simultaneous nor sequential releases, except in one of the sequential release where P. scabriventris was released second, with its sex ratio significantly female-biased. Non-reproductive host mortality was not important for both parasitoids when used alone and in combined releases compared to the natural mortality observed in the control. These findings suggest that P. scabriventris has no detrimental effect onO. dissitus and its release into Kenyas agricultural ecosystems will enhance the management of Liriomyza leafminer.

Performance of Apanteles hemara (Hymenoptera: Braconidae) on two Amaranth Leaf-webbers: Spoladea recurvalis and Udea ferrugalis (Lepidoptera: Crambidae)

Abstract Amaranth is an African indigenous vegetable that is gaining popularity due to its nutritional, medicinal, and economic values. In East Africa, frequent outbreaks of Lepidopteran leaf-webbers, Spoladea recurvalis F. (Lepidoptera: Crambidae) and Udea ferrugalis Hübner (1976) are reported on this crop, causing up to 100% foliage loss. The larval endoparasitoid Apanteles hemara Nixon is also frequently found associated with these pests during the outbreaks, however, its performance on both pests has never been documented. Laboratory studies were therefore carried out to assess the acceptability and suitability of S. recurvalis and U. ferrugalis to A. hemara. Both leaf-webber species were accepted by and suitable for the parasitoid. The mean host searching time and oviposition attempts were neither affected by rearing host nor test host. The total developmental time of A. hemara ranged between 10.6 ± 0.16 and 12.8 ± 0.30 days on both hosts. The sex ratio of the parasitoid was female biased when reared on S. recurvalis but male biased on U. ferrugalis. When offered 50 larvae of leaf-webbers for 24 h, a single female A. hemara achieved parasitism rates from 42.63 ± 5.80 to 44.55 ± 5.95, while a cohort of five females resulted in parasitism rates between 87.25 ± 2.70 and 94.67 ± 1.98 %. There was no significant difference between hosts in regard to progeny fitness at each parasitoid density. The parasitoid also caused significant nonreproductive larval mortalities in the hosts. The implications of these findings for mass rearing of the parasitoid as well as for conservation and augmentative biological control of amaranth lepidopteran leaf-webbers in East Africa are discussed.

Seasonal occurrence of amaranth Lepidopteran defoliators and effect of attractants and amaranth lines in their management

Lepidopteran defoliators are the most important pests of cultivated amaranths causing severe losses in cultivated fields worldwide. Leaf‐webbers, whose larvae fold, web or glue amaranth leaves using their silken webs as they feed and leaf‐worms which cause windowing but do not glue or fold leaves are mainly reported. Sustainable management strategies for these pests are still lacking given the adverse effects of synthetic pesticides. Field experiments were conducted during two seasons at two different sites in Central Kenya, to assess amaranth lepidopteran pests and their natural enemies’ population dynamics, evaluate the efficacy of phenylacetaldehyde (PAA) floral lure as attractant and the effects of three amaranth lines (Abuk1, Abuk2 and Abuk8) on the pests’ abundance and damage. Abundance of leaf‐webbers (p = .537), leaf‐worms (p = 1) and their associated parasitoids (p = .083) did not differ between the dry and wet seasons. The parasitoids Atropha tricolor and Apanteles sp. caused parasitism of 6.2% and 33.3% on Spoladea recurvalis and Choristoneura sp., respectively. PAA incorporated traps attracted moths that were largely unrelated to the damaging larvae observed on the crops with only 0.5% of total trap catches being S. recurvalis. Sub‐sites in which PAA were incorporated had significantly higher number of leaf‐webber larvae on the crops compared to control sub‐sites (p = .014). Amaranth lines studied had significant (p = .007) effect on lepidopteran defoliators’ abundance and damage, with fewer leaf‐webbers and lower severity of damage recorded on Abuk2 compared to Abuk8. The implication of these findings for the control of lepidopteran defoliators in East Africa is discussed.

Fungal Endophytes: Beyond Herbivore Management

The incorporation of entomopathogenic fungi as biocontrol agents into Integrated Pest Management (IPM) programs without doubt, has been highly effective. The ability of these fungal pathogens such as Beauveria bassiana and Metarhizium anisopliae to exist as endophytes in plants and protect their colonized host plants against the primary herbivore pests has widely been reported. Aside this sole role of pest management that has been traditionally ascribed to fungal endophytes, recent findings provided evidence of other possible functions as plant yield promoter, soil nutrient distributor, abiotic stress and drought tolerance enhancer in plants. However, reports on these additional important effects of fungal endophytes on the colonized plants remain scanty. In this review, we discussed the various beneficial effects of endophytic fungi on the host plants and their primary herbivore pests; as well as some negative effects that are relatively unknown. We also highlighted the prospects of our findings in further increasing the acceptance of fungal endophytes as an integral part of pest management programs for optimized crop production.

Prospects of endophytic fungal entomopathogens as biocontrol and plant growth promoting agents: An insight on how artificial inoculation methods affect endophytic colonization of host plants

Entomopathogenic fungi (EPF) can be established as endophytes in the host plants to offer a long-term preventive measure for pests and diseases. This practice serves as a better alternative to the common practice of periodic direct application of EPF on plants or the target pests as a short-term defense strategy against pests and diseases. These fungal endophytes, aside from their role in pests and diseases prevention, also act as plant growth promoters. Several fungal endophytes have been associated with improvement in plant height, dry and wet weight and other growth parameters. However, many limiting factors have been identified as mitigating the successful colonization of the host plants by EPF. The inoculation methods used have been identified as one, but sadly, this has received little or less attention. Some previous studies carried out comparison between various artificial inoculation methods; foliar application, seedling dipping, soil drenching, seed inoculation, direct injection and others. In separate studies, some authors had suggested different application methods that are best suitable for certain fungal entomopathogens. For instance, leaf inoculation with conidial suspensions was suggested to be the best inoculation method for Beauveria bassiana in sorghum, stem injection was suggested as the most suitable for coffee, while, root dipping method proved the most successful for B. bassiana colonization of tomato plants for the management of Helicoverpa armigera. Here, we discussed entomopathogenic fungal endophytes as bio-control agents, plant growth promoters and highlighted the effect of various artificial inoculation methods on their endophytic colonization of the host plants.

Bemisia tabaci-mediated facilitation in diversity of begomoviruses: Evidence from recent molecular studies

Begomoviruses are considered as one of the most notorious plant viruses worldwide, which cause substantial economic losses to various field crops. Management of begomoviruses has become a challenge due to the continuous evolution and the emergence of new strains. Bemisia tabaci is globally known to be the key vector of begomoviruses, having relatively high reproductivity, fast dispersal ability, high survival rate due to its polyphagous nature and high resistance to various groups of insecticides. Continuous transmission of begomoviruses by the vector has led to the development and spread of epidemics of various diseases worldwide. In this review, we have critically analyzed the various dynamics which facilitate the diversity of begomoviruses through their vector. The interaction of begomovirus-whitefly leads to continuous research activities regarding management of both virus and its vector, thus opening exciting new horizons to formulate potential control strategies to ensure a disease-free cropping environment.