Spatial and Temporal Distribution of Leafhoppers (Hemiptera: Cicadellidae) in a Corn Field

Leafhoppers (Hemiptera: Cicadellidae) are phytophagous insects that transmit diseases and cause damage to this crop. Thus, the main goal of this study was to verify the spatiotemporal behavior of the leafhoppers Tapajosa ocellata (Osborn, 1926), Dechacona missionum (Berg, 1879), and Dalbulus maidis (DeLong, 1923) in a corn field in Igarapé-Açu, northeastern Pará, northern Brazil. An area of 1.0 ha was used for the development of the study. A mango agroecosystem, a pasture, and secondary forest fragment are adjacent to the experimental area. The sampling of leafhoppers occurred during the 2015 and 2016 harvests. For sampling, 10 random plants per plot were analyzed, totaling 1000 plants per sample. In order to verify the occurrence of leafhoppers, all aerial parts of the plants were analyzed visually. The spatiotemporal behavior of leafhoppers and influence of adjacent areas and phenological stages of corn were verified through geostatistics. From the composition of semivariograms, interpolation maps were constructed by kriging. The results showed that, in 2015, there was a higher incidence of D. maidis compared to the following year. In 2016, 352 individuals of T. ocellata and 66 of D. missionum were observed. Regarding the spatial distribution, it was found that the smallest area of influence of T. ocellata, D. missionum, and D. maidis was 0.09, 0.08, and 0.05 ha, respectively. The spatial distribution of leafhoppers showed an aggregate behavior concentrated close to adjacent areas with a predominance of grasses. Population fluctuation demonstrated that the highest incidence of leafhoppers occurs in the vegetative stages of corn.

Phytophagous insects and natural enemies in kale under organic and chemical fertilizers

ABSTRACT: Organic agriculture is distinguished by practices that benefit the environment and support sustainable agriculture. In the present study, leafy kale, Brassica oleracea L. var. acephala DC., was submitted to chemical and organic (castor bean cake and bovine manure) fertilization treatments aiming to verify the influence of these fertilizers on the occurrence of insect pests and natural enemies. The insects were sampled by visual examination of plants and pitfall traps. Brevicoryne brassicae (L.) and Myzus persicae (Sulzer) (Hemiptera: Aphididae) were the phytophagous insects that occurred more significantly in kale, under chemical rather than organic fertilization, whereas Harmonia axyridis (Pallas), Hippodamia convergens (Guérin-Méneville) (Coleoptera: Coccinellidae), Diaeretiella rapae (M’Intosh) (Hymenoptera: Braconidae) and spiders (Arachnida: Araneae) were abundant in kale under organic fertilizer. The study showed that castor bean cake and bovine manure as leafy kale fertilizers can reduce the use of insecticides and provide quality food.