Distribution of Dalbulus maidis (DeLong) (Hemiptera: Cicadellidae) and incidence of maize rayado fino virus and Candidatus Phytoplasma asteris in corn succession planting systems.

BACKGROUND: Corn is one of the main crops grown globally to produce food for human consumption and animal feed, including raw materials for bioenergy. Effective pest management is critical for the economic viability of corn production. The leafhopper Dalbulus maidis and the diseases transmitted by it have become relevant to corn production. Our study aimed to determine environmental parameters that affect D. maidis populations and the impacts of pathogen dispersion on corn productivity under different rotation systems and sowing seasons. RESULTS: The population density of leafhoppers found in the studied crops was low but capable of establishing the diseases and spreading them widely in the crops. The leafhopper's highest occurrence was in the corn vegetative development stage, and its population peaks were earlier in the corn off-season. The incidence of maize rayado fino virus and maize bushy stunt phytoplasma were higher in corn off-season than in the growing season. The incidence of diseases was higher in the final stages of the cultivation cycle. Yield losses were significantly higher for maize bushy stunt phytoplasma and not significant for maize rayado fino virus. CONCLUSION: Our study observed that corn's physiological stage was the main factor influencing D. maidis dynamics. The occurrence of D. maidis at low densities was sufficient to ensure the efficient transmission and dissemination of maize rayado fino virus and maize bushy stunt phytoplasma, which had a higher incidence in the reproductive stage and the corn sowed off-season. © 2023 Society of Chemical Industry.

Potential interactions between herbivorous arthropods and of their natural enemies on Caryocar brasiliense (Caryocaraceae) trees

ABSTRACT The study of arthropod communities foraging on monocultures of native plants (e.g. Caryocar brasiliense) in biodiversity hotspots (e.g. Brazilian Cerrado) is important to understand the processes driving their performance. This study evaluated the possible interactions between galling herbivores, free-feeding arthropods, and of their natural enemies on C. brasiliense trees, in an orchard (monoculture). The possible competition observed were: i) between galling insects with defoliators and phytophagous mites, ii) between sucking insects, iii) between phytophagous mites and, iv) between Aphis gossypii (Hemiptera: Aphididae) with Histiostoma sp. (Acari: Histiostomidae) on C. brasiliense trees. Numbers of predators and prey, parasitoids and hosts, and predators and parasitoids were directly related among them. The competitive interactions between herbivorous predator and parasitoid may reduce Eurytoma sp. (Hymenoptera: Eurytomidae) populations, a potential pest of C. brasiliense. The predator Zelus armillatus (Hemiptera: Reduviidae) and the parasitoids Sycophila sp. (Hymenoptera: Eurytomidae) and Ablerus magistretti (Hymenoptera: Aphelinidae) are important to determine the numbers of Eurytoma sp. and of its galls. These natural enemies may be important to control this galling insect on C. brasiliense trees. The arthropod competition affected their guild associated to C. brasiliense trees.

Architectural diversity and galling insects on Caryocar brasiliense trees.

Galling insects are a highly sophisticated herbivore group on Caryocar brasiliense, a tree that represents the main income source for many communities. The effect of architectural diversity of C. brasiliense trees on galling insect community diversity and abundance was studied. The abundance of adult insects and galled leaves were seven and 1.6 times higher in trees with a greater height/width of canopy (RHW) ratio, respectively. Gall parasitoid richness was 1.8 times greater on trees with higher RHW. Zelus armillatus (Lepeletier & Serville) (Hemiptera: Reduviidae) and ant numbers were 5.8 and 2.7 higher on trees with the largest and smallest RHW, respectively. More complex plant architectures favored species diversity for galling insects and their natural enemies. The competition among four galling insect species for space and feeding and the evidence of "prudence strategy" were, for the first time, observed for galling insects in the Brazilian Cerrado biome.

Within tree distribution of a gall-inducing Eurytoma (Hymenoptera, Eurytomidae) on Caryocar brasiliense (Caryocaraceae) / Distribuição espacial de galhas induzidas por Eurytoma (Hymenoptera, Eurytomidae) em plantas de Caryocar brasiliense (Caryocaraceae)

For the first time, we identified the insect herbivore that induces one of the most conspicuous galls on the leaves of Caryocar brasiliense Camb. (Caryocaraceae), a widespread, typical cerrado woody plant of large economic importance. The gall inducing organism is a new and undescribed species of Eurytoma sp. (Hymenoptera, Eurytomidae). Furthermore, we recorded its spatial distribution within C. brasiliense trees. More Eurytoma galls were found on the eastern tree slope, followed the southern and northern slopes. More galls were found in the interior of the tree crown, i.e., on the proximal portion of the stems compared to the terminal portion. At the leaf level, more galls were found on the median region compared to the distal or proximal, perhaps due to the lower trichome density found in there. Leaf colonization by Eurytoma sp. may initiate at the leaf margin but after colonization reaches 50 percent the central portion starts to be colonized.

Pela primeira vez foi identificado o inseto herbívoro que induz uma das galhas foliares mais conspícuas em Caryocar brasiliense Camb. (Caryocaraceae), uma planta amplamente distribuída no Cerrado brasileiro e de relevante importância econômica. O galhador identificado, preliminarmente, como uma nova espécie ainda não descrita de Eurytoma (Hymenoptera, Eurytomidae). Além disso, foi observado a distribuição espacial desse galhador na copa das árvores de C. brasiliense. O lado leste da planta apresentou maior abundância de galhas de Eurytoma sp. seguido pelos lados sudeste e nordeste. No interior da copa houve um maior número de galhas em relação à porção mais externa. Em relação às folhas, a maior abundância ocorreu na porção mediana comparada às regiões proximal e distal, provavelmente devido ao menor número de tricomas na porção mais central da folha. Após colonizar cerca de 50 por cento das folhas marginais Eurytoma sp. inicia a colonização das folhas na porção central da folha.