Melon (Cucumis melo L.; Cucurbitaceae) is one of the 10 most-consumed fruits in the world. The whitefly Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) is one of the most important pests in melon crops worldwide. Conventional sampling plans are the starting point to establish decisionmaking systems for integrated pest management (IPM) programs. The purpose of this study was to determine a conventional sampling plan for B. tabaci in melon crops with plants at the vegetative, flowering, and fruiting stages. The best sampling units for B. tabaci were the 5th and 6th most apical leaves of the plant vine. The best sampling technique was direct counting of adult whiteflies. The most appropriate frequency distribution to describe B. tabaci densities in melon fields was the negative binomial. Whiteflies on melon fields with plants at different phenological stages showed a common aggregation parameter (Kcommon = 0.9134). The optimal number of samples from the sampling plan was 72 samples per field with a maximum error of 15% in population determination. The sampling plan determined by this study can be used by farmers because it is a low-cost (US$5.27 per sampling), fast (39 minutes per sampling) and feasible (15% maximum evaluation error). The same sampling plan can be used with melon plants at the vegetative, flowering, and fruiting stages.

Watermelon, Citrullus lanatus (Thunb.) Matsum. & Nakai (Cucurbitales: Cucurbitaceae), is one the 5 most-consumed fresh fruits in the world. The thrips Frankliniella schultzei (Trybom) (Thysanoptera: Thripidae) is an important pest of watermelon crops in tropical regions. Among the principal factors that regulate pest populations in crops are phenological stage of the host plant, weather and climate, and natural enemies. Thus, knowledge of such factors may allow the prediction of the risk of pest damage to such crops. The objective of this study was to identify factors that drive F. schultzei population densities in watermelon crops. During 2014 and 2015, we evaluated the effect of abiotic (weather) and biotic (phenological stage of leaves, and occurrence of natural enemies) factors on F. schultzei population densities on watermelon commercial crops. Frankliniella schultzei densities were higher in dry periods with more intense winds. Insect pest density was higher on younger leaves of plants in the vegetative stage. Frankliniella schultzei preferred to attack younger leaves of the plant located at the apex of the branches. The results obtained in this work suggest that the population growth of F. schultzei in watermelon crops is higher in periods of low rainfall. The population densities of F. schultzei depend on the phenological stage of plants, weather, and populations of natural enemies. Farmers should seek to preserve the populations of Chrysoperla sp. (Neuroptera: Chrysopidae), which are an important natural enemy of F. schultzei.

We evaluated the efficacy and residual toxicity of nine commercial insecticides on Plutella xylostella and their selectivity to the predator ant Solenopsis saevissima under laboratory and field conditions. First, to test the insecticides’ effectiveness and selectivity, we conducted concentration-response bioassays on both species and the mortalities were recorded 48 h after exposure. Next, rapeseed plants were sprayed following label rate recommendations in the field. Finally, insecticide-treated leaves were removed from the field up to 20 days after application and both organisms were exposed to them as in the first experiment. Our concentration-response bioassay indicated that seven insecticides caused mortality ≥80% of P. xylostella: bifenthrin, chlorfenapyr, chlorantraniliprole, cyantraniliprole, indoxacarb, spinetoram, and spinosad. However, only chlorantraniliprole and cyantraniliprole caused mortality ≤30% of S. saevissima. The residual bioassay indicated that four insecticides had a long-lasting effect, causing mortality of 100% to P. xylostella 20 days after application: chlorantraniliprole, cyantraniliprole, spinetoram, and spinosad. For S. saevissima, bifenthrin caused mortality of 100% during the evaluated period. Additionally, mortality rates below 30% occurred four days after the application of spinetoram and spinosad. Thus, chlorantraniliprole and cyantraniliprole are safe options for P. xylostella management since their efficacy favor S. saevissima.