Parasitism of Plutella xylostella (L.) (Lepidoptera: Plutellidae) Populations on Cabbage Brassica oleracea var. capitata (L.) by Cotesia plutellae (Kurdjumov) (Hymenoptera: Braconidae) in Ghana

The study was carried out at the Weija Irrigation Company site at Weija, in the Greater Accra Region of Ghana, to determine the seasonal abundance of the major parasitoid of Plutella xylostella (L.) populations on cabbage, Brassica oleracea var. capitata (L.) during the rainy and the dry seasons. The results indicated that Cotesia plutellae (Kurdjumov) was the most abundant and important parasitoid of P. xylostella on cabbage. It accounted for about 92% of the parasitoids, and occurred in all the three seasons of planting. The rest consisted of four facultative hyperparasitoids: Oomyzus sokolowskii, Aphanogmus reticulatus, Elasmus sp. and a Trichomalopsis sp., and two primary parasitoids, Pediobius sp. and Hockeria sp. A significantly higher rate of parasitism (68.6 ± 12.9%, P < 0.05) of P. xylostella by C. plutellae occurred during the major rainy season and the least (9.9 ± 7.1) in the minor rainy season. Cotesia plutellae acted in a density dependent manner, and its numbers increased as that of the host in all three seasons. The coefficient of correlation was highest in the major rainy season (r = 0.97) with a coefficient of determination of 0.97. In the minor rainy season r = 0.55, and in the dry season r = 0.66. The annual coefficient of correlation was r = 0.51 and the coefficient of determination = 0.262. Hence, in an annual production of cabbage, 26.2% of the variation in parasitism was due to the variation in the number of P. xylostella. The results, therefore, indicate that C. plutellae can be used in the development of an integrated pest management programme (IPMP), against P. xylostella in Ghana

Development of a Bait System for the Pharaoh’s Ant, Monomorium Pharaonis L. (Hymenoptera: Formicidae)

The infestation of the Pharaoh’s ant, Monomorium pharaonis L. is widespread and, sometimes, very serious in homes, hospitals, restaurants, factories, etc. People are helpless because effective baited traps are not available locally, and little has been done locally to develop effective control strategies for these ants. The study aimed at developing an appropriate bait system from local materials for the control of the Pharaoh’s ant. Nine baits and three insecticides were evaluated in the laboratory and field situations. Groundnut cake, dry fish and granulated sugar were the most attractive baits. Rimon (a Benzoylphenyl urea), an insect growth regulator, was the most promising insecticide for incorporation into the bait system. It is, therefore, recommended that a bait system, containing groundnut cake, sugar and dry fish, mixed with 1% Rimon, be evaluated for Pharaoh’s ant control

Differential effects of weather, plant phenology and predators on the seasonal variation of aphids on cabbage

The aphids Lipaphis erysimi pseudobrassicae (Davis) and Myzus persicae (Sulzer) pose serious threats to the production of cruciferous crops in the tropics. Understanding their population dynamics is important for developing integrated pest management programmes to minimize their damage to crops. This study investigated the effects of climatic factors, natural enemies and plant age on the population dynamics of these pests. The population density of aphids and their natural enemies in 20 cabbage plants, and weather conditions were monitored for five cropping seasons from 2019 to 2021 in two agroecological zones of Ghana (Coastal Savannah and Deciduous Forest zones). The highest population density of L. e pseudobrassicae was recorded in January (dry season) in both agroecological zones, while the highest population density for M. persicae occurred in September (minor rainy season) and August (dry spell) in the Coastal Savannah and Deciduous Forest zones, respectively. The highest aphid densities were noted to occur during periods with low relative humidity and low rainfall. The population density of L. e. pseudobrassicae was significantly negatively related to plant age, air temperature and relative humidity, and positively related to syrphids (Paragus borbonicus) and spiders in the Coastal Savannah zone, while in the Deciduous Forest zone it was significantly positively related to coccinellids. On the other hand, M. persicae population density was significantly positively related to syrphids and coccinellids in the Deciduous Forest zone. Rainfall negatively affected syrphids in the Coastal Savannah zone, while air temperature positively affected syrphids and negatively affected spiders in the Deciduous Forest zone. Coccinellids had a significant positive relationship with relative humidity in the Deciduous Forest zone. This study provides important insights into the key factors that regulate aphid population densities on cabbage and will support development of timely interventions to manage these pests.Funding was provided by the German Academic Exchange (DAAD) for the PhD studies of FEE, the BBSRC CONNECTED Network Grant (BB/R005397/1) to K.O.F and J.P.C

Differential effects of weather, plant phenology and predators on the seasonal variation of aphids on cabbage

The aphids Lipaphis erysimi pseudobrassicae (Davis) and Myzus persicae (Sulzer) pose serious threats to the production of cruciferous crops in the tropics. Understanding their population dynamics is important for developing integrated pest management programmes to minimize their damage to crops. This study investigated the effects of climatic factors, natural enemies and plant age on the population dynamics of these pests. The population density of aphids and their natural enemies in 20 cabbage plants, and weather conditions were monitored for five cropping seasons from 2019 to 2021 in two agroecological zones of Ghana (Coastal Savannah and Deciduous Forest zones). The highest population density of L. e pseudobrassicae was recorded in January (dry season) in both agroecological zones, while the highest population density for M. persicae occurred in September (minor rainy season) and August (dry spell) in the Coastal Savannah and Deciduous Forest zones, respectively. The highest aphid densities were noted to occur during periods with low relative humidity and low rainfall. The population density of L. e. pseudobrassicae was significantly negatively related to plant age, air temperature and relative humidity, and positively related to syrphids (Paragus borbonicus) and spiders in the Coastal Savannah zone, while in the Deciduous Forest zone it was significantly positively related to coccinellids. On the other hand, M. persicae population density was significantly positively related to syrphids and coccinellids in the Deciduous Forest zone. Rainfall negatively affected syrphids in the Coastal Savannah zone, while air temperature positively affected syrphids and negatively affected spiders in the Deciduous Forest zone. Coccinellids had a significant positive relationship with relative humidity in the Deciduous Forest zone. This study provides important insights into the key factors that regulate aphid population densities on cabbage and will support development of timely interventions to manage these pests.Funding was provided by the German Academic Exchange (DAAD) for the PhD studies of FEE, the BBSRC CONNECTED Network Grant (BB/R005397/1) to K.O.F and J.P.C