Susceptibility of two spotted spider mite Tetranychus urticae KOCH (Acari; Tetranychidae) to some selected miticides in the Greater Accra Region of Ghana

The two-spotted spider mite Tetranychus urticae is a serious pest of vegetables, fruits and field crops in Ghana but hardly noticed by farmers. A recent survey in parts of Greater Accra Region revealed that farmers do not specifically target T. urticae in terms of control but use insecticides at high dosages and at short intervals to address the complex of pest affecting their crops. This practice is a recipe for resistance development in mite pest. Susceptibility studies were carried out using five miticides, lambda cyhalothrin, emamectin benzoate, prosular oxymatrine, imidacloprid and sulphur. Adult T. urticae were collected from four suburbs in Accra (Opeibea, Ashaiman, University of Ghana Farm and Department of Crop Science Sinna Garden). These populations were used to raise colonies on garden egg plants in separate laboratories. Infested leaves were taken from the plants and sprayed with serial dilutions of the miticides and mortality recorded after 24 h. The LD50 values and slopes were determined using probit analysis and resistance factors calculated. All field populations were quite resistant to Karate® (up to 21.6-fold) but were susceptible to the other four products where resistance factors were quite low. The University of Ghana Farms, Sinna Garden and Ashaiman populations were susceptible to Imidacloprid except the Opeibea population which showed a low level of resistance (9-fold). Synergism assays using piperonyl butoxide (0.4 μL/mL) and Diethyl maleate (1.0 μL/mL) on the Karate®-resistant population showed that the application of these products 1 h before treatment with Karate® reduce resistance in the Opeibea population from 21-fold to between 2.9 to 4.3-fold whereas that of Ashaiman was reduced from 19-fold to 2.6-fold suggesting the involvement of glutathione-S-tranferases (GSTs) and cytochrome P450 monooxygenases and esterases as the possible mechanisms of resistance.© 2016 International Formulae Group. All rights reserved.Keywords: Tetranychus urticea, resistance, glutathione-S-tranferases, cytochrome P450 monooxygenases, esterases, piperonyl butoxide, diethyl maleate

Insecticide susceptibility of bemisia tabaci to karate® and cydim super® and its associated carboxylesterase activity

Bemisia tabaci is a pest of several economic crops worldwide and is mostly managed in Ghana by farmers through the use of insecticides. However, vegetable farmers have recently expressed concerns about the susceptibility of B. tabaci to insecticides. Hence, the susceptibility status of field populations of B. tabaci on cassava, okra and tomato in vegetable growing sites in Accra to two commonly used insecticides, Karate® 2.5 EC (λ-cyhalothrin) and Cydim Super® (36 g Cypermethrin + 400 g Dimethoate per litre), using a modified dipping method and their carboxylesterase activity levels were assessed. The LC50 values of the B. tabaci populations to the insecticides were low and ranged from 0.12-0.55 mL/L to 0.07-0.36 mL/L for Karate® and Cydim Super®, respectively. There was a wide variation in carboxylesterase activity levels of the insect populations with high levels recorded in some of the populations. The elevated activity levels could negatively impact on future whitefly management methods. This study provides baseline information on the insecticide resistance status and carboxylesterase levels of whitefly populations in these areas and for monitoring future insecticide resistance development

SORGHUM HEAD BUG INFESTATION AND MOULD INFECTION ON THE GRAIN QUALITY OF SORGHUM IN NORTHERN GHANA

Sorghum ( Sorghum bicolor ) panicle is reported to be attacked by a myriad of insect pest species, whose infestation predisposes the grains to fungal infection, thereby compromising their quality. A complex of bugs has been reported to infest sorghum, thereby affecting quality of grains in West Africa. The objective of this study was to investigate the effect of head bug ( Eurystylus oldi (POPPIUS) infestation and mould infection on sorghum grain quality. An experiment consisting of eight sorghum breeding lines (two parental checks and six F8 derivatives), was carried out in fields at three Agro-ecological Zones (Nyankpala, Damongo and Manga) in Northern Ghana. Results showed that damage caused by head bug populations per panicle were not significant (P>0.05). Head bug damage was, however, found to be highly correlated with panicle grain mould ratings (PGMR) at all three locations. This points to the significant roles head bug damage plays in fungal infection of sorghum grains. The derivatives, on the other hand, suffered less PGMR than the compact headed Kapaala, across the three locations. The three dominant fungi isolated at Manga and Nyankpala included those of the genera Curvularia sp. (31.6 and 31.4%, respectively), Fusarium sp. (22.3 and 27.6%, respectively) and Thielaviopsis sp. (20.3 and 20.9%, respectively). At Damongo, Fusarium sp. (29.6%), Curvularia sp. (23.6%) and Mucor sp. (17.2%) were dominant. Grain quality, in terms of head bug and mould damage ratings, showed the following lines emerging superior at Manga (SARSORG-MRG-2011-3, SARSORG-SBG-2011-5 and SARSORG-SRG-2011-6), at Damongo (SARSORG-TRG-2011-1, SARSORG-SBG-2011-5 and SARSORG-MBG-2011-4) and at Nyankpala (SARSORG-MBG-2011-4, SARSORG-MRG-2011-3 and SARSORG-TRG-2011-1) and; thus suggest they may possess some desirable traits for which they could be selected for further improvement.La panicule du sorgho ( Sorghum bicolor ) a \ue9t\ue9 rapport\ue9e d\u2019\ueatre attaqu\ue9e par une multitude d\u2019esp\ue8ces d\u2019insectes pestes, dont l\u2019infestation pr\ue9dispose les grains \ue0 l\u2019infection des champignons, par cons\ue9quent compromet leur qualit\ue9. Un complexe de punaises a \ue9t\ue9 rapport\ue9 d\u2019infester le sorgho, donc affecte la qualit\ue9 des grains en Afrique de l\u2019Ouest. L\u2019objectif de cette \ue9tude \ue9tait d\u2019investiguer l\u2019effet de l\u2019infestation des punaises de t\ueate ( Eurystylus oldi , POPPIUS) et des moisissures sur la qualit\ue9 des grains du sorgho. Une exp\ue9rimentation comportant huit lign\ue9es am\ue9lior\ue9es du sorgho (deux contr\uf4les parentaux et six F8 d\ue9riv\ue9es), \ue9tait conduite au champ en trois zones agro-\ue9cologiques (Nyankpala, Damongo et Manga) au Nord du Ghana. Les r\ue9sultats ont montr\ue9 que les dommages caus\ue9s par les populations de punaises de t\ueate sur la panicule n\u2019\ue9taient pas significatifs (P>0,05). Le dommage de la punaise de t\ueate \ue9tait, toutefois, retrouv\ue9 hautement corr\ue9l\ue9 avec les scores de panicule de grains moisies (PGMR) \ue0 toutes les trois locations. Ceci montre le r\uf4le significatif que joue la punaise de t\ueate dans l\u2019infection fongique des grains du sorgho. Les d\ue9riv\ue9es, d\u2019autre part, ont souffert moins de PGMR que le Kapaala \ue0 t\ueate compacte, \ue0 travers les trois locations. Les trois champignons dominants isol\ue9s \ue0 Manga et Nyankpala comprennent ceux du genre Curvularia sp. (31,6 et 31,4%, respectivement), Fusarium sp. (22,3 et 27,6%, respectivement) et Thielaviopsis sp. (20,3 et 20,9%, respectivement). A Damongo, Fusarium sp. (29,6%), Curvularia sp. (23,6%) et Mucor sp. (17,2%) \ue9taient dominants. La qualit\ue9 du grain, en termes des scores du dommage de punaise de t\ueate et des moisissures, a montr\ue9 que les lign\ue9es suivantes \ue9taient sup\ue9rieures \ue0 Manga (SARSORG-MRG-2011-3, SARSORG-SBG-2011-5 et SARSORG-SRG-2011-6), \ue0 Damongo (SARSORG-TRG-2011-1, SARSORG-SBG-2011-5 et SARSORG-MBG-2011-4) et \ue0 Nyankpala (SARSORG-MBG-2011-4, SARSORG-MRG-2011-3 et SARSORG-TRG-2011-1) et\ua0; donc sugg\ue8re qu\u2019ils pourraient poss\ue9der quelques traits d\ue9sirables pour lesquels ils pourraient \ueatre s\ue9lectionn\ue9s pour une meilleure am\ue9lioration

Natural enemies of the fall armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) in Ghana

Open Access JournalThe fall armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), is an invasive insect pest attacking maize in Ghana and sub-Saharan Africa countries. Biological control will need to be an important management strategy, and a first step was to identify potential natural enemies. Sampling was conducted in different localities of the 10 regions of Ghana from May to Nov 2017. A total of 1,062 larvae were collected from 106 maize farms, and the presence of natural enemies was recorded in 18 (17.0%) farms. Among natural enemies recorded, 7 species were parasitoids: Chelonus bifoveolatus Szpligeti, Coccygidium luteum (Brull), Cotesia icipe Fernandez, Meteoridea testacea (Granger), and Bracon sp. (all Hymenoptera: Braconidae), Anatrichus erinaceus Loew (Diptera: Chloropidae), and an undetermined tachinid fly (Diptera: Tachinidae). The parasitism rate was 3.58%. Three predator species were collected: Pheidole megacephala (F.) (Hymenoptera: Formicidae), Haematochares obscuripennis Stål, and Peprius nodulipes (Signoret) (both Heteroptera: Reduviidae). The 2 most abundant parasitoids were C. bifoveolatus and C. luteum with a relative abundance of 29.0% and 23.7%, respectively, and a parasitism rate of 1.04% and 0.85%, respectively. However, C. bifoveolatus was the most dispersed parasitoid, found in 6.6% of the inspected sites within all the agroecological zones of Ghana. This species is a good candidate as a biological control agent for fall armyworm in Africa. The predator that was most abundant (46.0%) and dispersed (3.8% of the farms) was P. megacephala. El cogollero, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), es una plaga de insectos invasora que ataca el maíz en Ghana y los países de África subsahariana. El control biológico deberá ser una estrategia de manejo importante, y un primer paso es identificar los enemigos naturales potenciales. Se realizó el muestreo en diferentes localidades de las 10 regiones de Ghana desde mayo hasta noviembre del 2017. Se recolectó un total de 1.062 larvas de 106 granjas de maíz, y se registró la presencia de enemigos naturales en 18 granjas (17.0%). Entre los enemigos naturales registrados, 7 especies fueron parasitoides: Chelonus bifoveolatus Szpligeti, Coccygidium luteum (Brull), Cotesia icipe Fernandez, Meteoridea testacea (Granger) y Bracon sp. (todos los Hymenoptera: Braconidae), Anatrichus erinaceus Loew (Diptera: Chloropidae) y una mosca taquinida indeterminada (Diptera: Tachinidae). La tasa de parasitismo fue del 3.58%. Se recolectaron tres especies de depredadores: Pheidole megacephala (F.) (Hymenoptera: Formicidae), Haematochares obscuripennis Stål y Peprius nodulipes (Signoret) (ambos Heteroptera: Reduviidae). Los 2 parasitoides más abundantes fueron C. bifoveolatus y C. luteum con una abundancia relativa del 29.0% y 23.7%, respectivamente, y una tasa de parasitismo del 1.04% y 0.85%, respectivamente. Sin embargo, C. bifoveotus fue el parasitoide más disperso, encontrado en el 6.6% de los sitios inspeccionados dentro de todas las zonas agroecológicas de Ghana. Esta especie es un buen candidato como agente de control biológico para el cogollero en África. El depredador que fue más abundante (46.0%) y disperso (3.8% de las granjas) fue P. megacephala

Influences of climate variability on cocoa health and productivity in agroforestry systems in Ghana

Open Access Article; Published online: 14 Oct 2022The susceptibility of cocoa to harsh climatic conditions is evident in cocoa growing areas in Ghana, and climate distribution models show reduced cocoa suitability to climate change. We assessed how cocoa health and productivity were affected by varying climate conditions for 4 years in 23 cocoa farms along a gradient of low rainfall/high temperature in the north to high rainfall/low temperature in the south of Ghana's cocoa belts. Twenty cocoa trees per farm (in total 460) were observed and scored for their canopy condition, flower intensity, and damaged pods due to mirids, cocoa shield bugs, and black pod disease (BPD). Harvested pods and extracted dried cocoa beans were evaluated to ascertain yield/productivity. Insect pest damages to pods were on average 2.3 ± 0.8, 2.2 ± 1.0, and 3.0 ± 0.7 pods tree−1 year−1 in the south, middle and north, respectively. The healthiest and highest yielding trees were in the rainy south at 0.99 ± 0.02 kg dry beans tree−1 followed by the middle (0.84 ± 0.02 kg) and the north (0.60 ± 0.01 kg). BPD infection was highest in the south at 1.1 ± 1.1 pods tree−1 year−1, followed by the middle (0.7 ± 0.8), and the north (0.4 ± 0.6). Within sites variability in rainfall and temperature was not found to affect yields significantly. The variability in cocoa performance and occurrence of pests and diseases observed within sites may thus be caused by farm management practices that are key to the enhancement of productivity at site level. We recommend regular pruning of cocoa and shade trees to increase aeration and prevent BPD in high rainfall areas, and an increase in shade tree components in dry regions for insect pest management in cocoa systems

Selected shade tree species improved cocoa yields in low-input agroforestry systems in Ghana

Open Access Article; Published online: 13 Aug 2022CONTEXT Cocoa agroforestry systems differ in the diversity of shade tree species composition. Though cocoa benefits from shade, there is a lack of species-specific information on shade trees that enhance soil fertility and yield. OBJECTIVE We examined how soil characteristics and cocoa yield were affected by eight commonly retained forest tree species, compared with unshaded control plots over a 3-year period. METHODS Using 74 circular plots from 10 cocoa farms in the Western region of Ghana, we sampled soils from two random points within each plot. Soil nutrients at the beginning and end of the study were analyzed, and yield was expressed as number of harvested pods and dry weight of beans per hectare. RESULTS AND CONCLUSIONS Levels of soil K and Ca were below recommended values. Although soil available phosphorus (P) was higher in control plots than under shade trees, yield around shade trees were higher than on unshaded plots. Cocoa yield differences between shade tree species and control plots were significant only in the major crop season, but not in the minor crop season. Cocoa yields under Cedrela odorata, Khaya ivorensis, Terminalia superba and Milicia excelsa were significantly higher than on control plots. Hence, the inclusion of specific shade tree species in cocoa agroforestry systems is important to maintain high yields in cocoa systems with low inputs. SIGNIFICANCE To our knowledge, this study presents one of the first attempt to assess the impacts of specific shade tree species on soil characteristics and cocoa yield

Resistance of Brazilian diamondback moth populations to insecticides

Plutella xylostella is a recurring pest on cruciferous crops around the world. In Brazil, it typically requires large number of insecticide sprays, which may lead to fast evolution of resistance. The aim of this study was to assess the susceptibility of Brazilian diamondback moth populations to the insecticides abamectin, deltamethrin, and spinosad. Leaf dip bioassays were used to determine mortality data obtained after 48 h of exposure to insecticides and subjected to Probit analysis. The population from Bonito, state of Pernambuco, Brazil, had the highest toxicity ratio (20.2 - fold) to abamectin compared to the reference population. The LC50 values for deltamethrin ranged from 85.2 to 360.1 mg L-1, demonstrating a high survival of populations in relation to this insecticide field dose rate (7.5 mg L-1). The toxicity ratios of the estimated LC50s, however, were very low (varying from 2.2 - to 4.2 - fold). Most populations exhibited toxicity ratios for spinosad, ranging from 2.3 - to 5.1 - fold, while both the LC50 and LC95 values reflected a high susceptibility to the spinosad field dosage (120 mg L-1). Only the Bonito - PE population resisted to abamectin, while all P. xylostella populations were resistant to deltamethrin, but particularly susceptible to spinosad because of the absence of selection pressure with it in these areas.Plutella xylostella é uma praga recorrente em brássicas de todo o mundo. No Brasil, normalmente exige grande número de pulverizações de inseticidas, que pode levar à rápida evolução da resistência. Avaliou-se a suscetibilidade de populações brasileiras da traça das crucíferas aos inseticidas abamectina, deltametrina e espinosade. Bioensaios de imersão de folhas foram utilizados para determinar a mortalidade, sendo os dados obtidos após 48 h de exposição aos inseticidas e submetidos à análise de Probit. A população de Bonito-PE apresentou a maior razão de toxicidade (20,2 vezes) para abamectina em relação à população de referência. Os valores de CL50s para deltametrina variaram entre 85,2 - 360,1 mg L-1, demonstrando alta sobrevivência das populações a este inseticida com relação à dose de campo (7,5 mg L-1). Entretanto, as razões de toxicidade das CL50 estimadas foram muito baixas (variando de 2,2 a 4,2 vezes). A maioria das populações apresentou razões de toxicidade para espinosade, variando de 2,3 para 5,1 vezes, embora os valores de CL demonstram alta suscetibilidade delas à dose de campo para espinosade (120 mg L-1). Apenas a população de Bonito PE apresentou resistência a abamectina, enquanto todas as populações de P. xylostella estão resistentes a deltametrina, mas suscetíveis ao espinosade particularmente devido à ausência de pressão de seleção com este nestas áreas