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Arthropods were sampled on an early- and late-season crop of watermelon in the 2016 cropping season using motorized suction sampler swept along 5m length of the middle row of 20 experimental plots at Federal University Wukari. Specimens were sorted to morphotypes, feeding guilds and as dominant based on percentage relative abundance (RA) and frequency of occurrence (FO). Different species diversity indices were computed. The collections made on the early- and late-sown crops were compared using Jaccard’s Similarity index (C_j). Spatial distribution pattern of the dominant arthropods were determined using Taylor’s power law and Iwao’s patchiness regression. Results showed that collections on both crops were similar (C_j= 0.83). A total of 14,466 specimens sorted to 1 order (Araneae) in the class Arachnida and 64 species in 41 families and 8 orders in the class Hexapoda were collected. Data showed moderately high species diversity (H = 2.8-3.0), richness (R = 6.0-7.2), but low evenness (E = 0.26-0.39). Coleopterous insects (22 species), dominated by chrysomelids, were the most diverse and species-rich followed by hymenopterans, mainly formicids. Dominant arthropods (RA≥1.0 and FO≥25.0%) included Asbecesta nigripennis, Aulacophora africana, Philanthus triangulum (parasitoid of bee), Pheidole sp., Camponotus sp., Rhynocoris nitidulus and spiders. Most dominant arthropods were aggregated; dispersion varied with model used and crop season. Only 27.3% of the diverse and rich arthropods on watermelon at Wukari require pest management intervention and validation of their dispersion pattern in large-scale watermelon production.

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The efficiency of neem based insecticides have been assessed by many studies however, there is scanty information on the cost:benefit ratio of their use vis-a-viz synthetics, particularly, in watermelon production. In this study, thirty-six 5 m long x 8 m wide plots were arranged in Randomized Complete Block Design in 4 replications of weekly spray of; 0.5% Cyper-diforce^® (CD); 1, 3 and 5% Neem Oil Emulsion (NOE); 0.25% CD + 1, 3 and 5% NOE; 1% soap solution and, Control (unsprayed plots). Arthropods were sampled on 5 m length of row using Suction Sampler and Yellow Sticky Board. Severity of leaf damage and aphid colony size was also assessed. At harvest, marketable fruits were weighed and used to compute cost-benefit ratio. The prevalent pests were five species of leaf-beetles, Aphis gossypii Glover, Bemisia tabaci (Gennadius), Bactrocera cucurbitae (Coquillett) and Helicoverpa armigera (Hubner). The beneficials included; Apis mellifera L., Cardiochiles niger Szépligeti and Cheilomenes sulphurea (Olivier). The 0.5% CD was ineffective against Aphids but 3 and 5% NOE were. Overall, insecticide treatments reduced infestation by 2.9-95.3%. Though, combination of 0.25% CD with NOE treatments suppressed pest infestation relative to sole neem oil treatments, leaf injury and yields were statistically comparable. Sole NOE treatments were observed not to significantly suppress populations of beneficials when compared to 0.25% CD or their combinations. 0.25% CD + 5% NOE consistently gave the highest yield/season (39192-44642 kgha^-1). Monetary benefits exceeded US$3724 ha^-1. The insignificant differences in yield among the insecticide treatments showcased neem’s potential in managing watermelon pests. The ineffectiveness of Cyper-diforce^® against A. gossypii suggests resistance development.