Eight Decades of Dalbulus maidis (DeLong & Wolcott) (Hemiptera, Cicadellidae) in Brazil: What We Know and What We Need to Know

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.

The Amazon and Its Biodiversity: a Source of Unexplored Potential Natural Enemies for Biological Control (Predators and Parasitoids)

The Amazon is an important source of natural enemies for biological control. The diversity of biocontrol agents in the Amazon is considerably higher than that in other Brazilian regions. However, few studies have focused on the bioprospecting of natural enemies in the Amazon. Furthermore, the expansion of agricultural land in recent decades has caused biodiversity loss in the region, including the loss of potential biocontrol agents, due to the replacement of native forests with cultivated areas and forest degradation. In this study, we reviewed the main groups of natural enemies in the Brazilian Legal Amazon: predatory mites (mainly Acari: Phytoseiidae), ladybirds (Coleoptera: Coccinellidae), and social wasps (Hymenoptera: Vespidae: Polistinae) and the Hymenoptera parasitoids of eggs (Trichogrammatidae) and of frugivorous larvae (Braconidae and Figitidae). The main species prospected and used in biological control are presented. The lack of knowledge and perspectives regarding these groups of natural enemies as well as the challenges of conducting research in the Amazon is discussed.

Corn Stunt Pathosystem and Its Leafhopper Vector in Brazil

Direct and indirect injury caused by Dalbulus maidis (Hemiptera: Cicadellidae) in corn is an ever-increasing concern in Brazil and other corn-producing countries of the Americas. This highly efficient vector transmits corn stunting pathogens and is of economic concern in the Neotropics, including temperate regions where epidemic outbreaks are now common. Despite the progress made so far, Brazilian corn growers continue to struggle with this pest and its associated pathosystem. In this review, we gathered relevant and updated information on the bioecology, population dynamics, and damaging potential of D. maidis. Our goal was to better understand its intimate association and complex interactions with the host crop and transmitted pathogens. Based on available scientific literature, we identified factors which explain the recent increase in D. maidis occurrence in South America, including the cultivation of corn during multiple growing seasons, overlapping of susceptible crops, and widespread use of genetically modified hybrids. The reasons for the overall inefficiency of current suppression strategies aimed at this pest are also summarized. Finally, a management program for D. maidis and corn stunt disease is proposed, combining strategies such as eradicating volunteer corn, reducing the planting period, using tolerant hybrids, and applying chemical and/or fungal insecticides. Prospects regarding the pest's status are also outlined. Overall, the information presented here will serve as a decision-making guide within Brazilian and South American corn production systems, as well as paving the way for devising novel strategies aimed at suppressing D. maidis populations and limiting the spread of corn stunt disease.

Intercropping maize with brachiaria can be a double-edged sword strategy

BACKGROUND

Intercropping is commonly implemented as a way of promoting sustainable agriculture. Some of the benefits of intercropping include improving resource-use efficiency and soil quality as well as promoting pest control. As for pest control, intercropping can often engender pest repellency/confusion and promote natural biological control. Nevertheless, intercropping is not always a win-win strategy for pest management, with chances of sometimes either favoring or hampering pests and their natural enemies. Brazilian farmers commonly row-intercrop maize with brachiaria with the intent of forming a grass pasture for the feeding of livestock after maize harvest. However, very little is known about whether this intercropping can influence key pests and natural enemies in the maize agroecosystem. The overall aim of this study was to investigate how multiple groups of maize pests and natural enemies respond in terms of temporal abundance to this intercropping.

RESULTS

Defoliation caused by caterpillars was higher in the intercropping treatment. Intercropping appeared to promote Dalbulus maidis while hampering aphids and Diabrotica speciosa. In general, the abundance of natural enemies was favored by intercropping. There was a reduction in maize productivity (i.e. fresh weight) in the intercropping treatment. Most results were season dependent.

CONCLUSION

We believe that by considering together the pros and cons of intercropping maize and brachiaria in terms of pest management and soil conservation/fertility, the benefits of implementing this intercropping shall still outweigh its potential challenges. Nevertheless, the results and ensuing recommendations should be considered under the context of time and arthropod species. © 2022 Society of Chemical Industry.

Spatial-temporal distribution of Dalbulus maidis (Hemiptera: Cicadellidae) and factors affecting its abundance in Brazil corn

BACKGROUND

Since the last decade, Dalbulus maidis has become the primary pest in cornfields, particularly due to its ability to transmit plant pathogens. Dalbulus maidis is the main vector of the corn stunt spiroplasma and maize bushy stunt phytoplasma. However, there is little information available on this pest. Understanding its spatial dynamics may allow us to determine how its infestations begin and to identify its colonization patterns, dispersal, and the role of landscape structure on D. maidis dynamics. Thus, this study aimed to investigate within-field spatial distribution and the factors associated with D. maidis abundance in five commercial fields.

RESULTS

In all fields, higher infestations occurred at the boundaries of the central pivot, showing a clear edge-biased distribution. Ranges varied from 100.4 to 611.8 m, and our models' overall fit indicated strong to moderate spatial dependency. Additionally, correlation analyses indicated a positive effect of air temperature on the population of D. maidis. Conversely, rainfall negatively affected D. maidis.

CONCLUSION

This study provides essential guidance for improving D. maidis integrated pest management at regional and local scales. Based on its high dispersal ability, our study suggests the need for a legislative or regulatory method of control for D. maidis, especially in regions where corn has more than one growing season. © 2022 Society of Chemical Industry.

Insecticide seed treatment against corn leafhopper: helping protect grain yield in critical plant growth stages

BACKGROUND

The corn leafhopper, Dalbulus maidis (Hemiptera: Cicadellidae), spreads maize stunt pathogens and requires timely and effective crop protection. We determined the interaction between maize phenology and the vector feeding/infection period by stunt pathogens with the residual efficacy of neonicotinoid insecticidal seed treatments. Greenhouse- and field-grown maize plants, seed-treated with clothianidin or imidacloprid insecticides, were infested during seven growth stages with corn leafhoppers reared under controlled conditions on maize plants displaying infection symptoms by both spiroplasma (corn stunt spiroplasma, Spiroplasma kunkelii) and phytoplasma (maize bushy phytoplasma) pathogens.

RESULTS

In the greenhouse and field settings, seed treatment reduced the stunt disease symptoms and corn yield loss during the VE-V4 maize growth stages and caused no phytotoxicity. The neonicotinoid seed treatment reduced 20-60% of the yield losses from the corn stunt disease until the V4 growth stage. Infestation by infective corn leafhoppers in the V12 maize growth stage caused a 25-30% yield loss irrespective of seed treatment, yet no stunt disease symptom was evident. Nonetheless, corn yield losses and visual stunt symptoms as rated by a nine-category ordinal scale were strongly correlated (r = 0.79, P < 0.01).

CONCLUSION

These results reinforce that maize plants are more susceptible to leafhopper stunt disease during the VE-V4 growth stages (emergence to the fourth-leaf stage). Seed treatment helps reduce the damage in the early growth stages (VE-V2), although supplemental control measures depending on leafhopper population density may be needed from VE-V12 to protect yield losses from the maize stunt condition. © 2021 Society of Chemical Industry.