Key Points
- The corn leafhopper (Dalbulus maidis) is one of the most important pests of corn in Latin America and the Caribbean.
- Corn leafhoppers are a vector for Spiroplasma kunkelii, a bacterial pathogen commonly referred to as corn stunt spiroplasma (CSS), which is the primary causal organism for corn stunt disease.
- Corn leafhoppers need warm temperatures and a living host for survival and reproduction, which keeps their range in the U.S. largely confined to the southernmost corn production areas.
Distribution and Pest Status
- The corn leafhopper (Dalbulus maidis) is one of the most important pests of corn in Latin America and the Caribbean, primarily because of its ability to transmit pathogens associated with corn stunt disease complex.
- D. maidis likely originated in the high valleys in the central region of Mexico, where it evolved alongside the wild ancestors of corn native to this region.
- As cultivation of corn spread throughout the tropical and subtropical regions of the Americas, corn leafhopper likely spread along with it, making it one of the earliest insect pests of corn production.
- The current range of the corn leafhopper in the Americas extends from the Southern U.S. to temperate parts of Argentina.
Lifecycle
- D. maidis begins as an egg and then undergoes five nymphal instars before reaching adulthood.
- Females insert eggs into the mesophyll of the upper surface of corn leaves, often in the whorls of corn seedlings.
- The first nymphal instar will hatch around 8 to 10 days after oviposition. First instars are less than 1 mm long and final instars are around 4 mm long.
- Each nymphal stage averages 3 to 4 days, with the total time to adulthood averaging 14 to 16 days.
- Adult longevity averages 60 to 80 days. Mature females oviposit an average of 15 eggs per day for most of their adult life.
- Corn leafhoppers do not enter any type of overwinter dormancy; populations survive as active adults.
- Under optimal conditions, corn leafhopper adults can survive without reproducing for up to three months.
Identification
- The adult corn leafhopper is light tan and about 1/8 of an inch long.
- Its most distinguishing feature is two dark spots located between the eyes (Figure 1).
- The nymphs have no wings and are green to tan in color.
- Both adults and nymphs feed inside the whorl, particularly in young corn. Later, as the plants grow, they move out onto the underside of the leaves.
Figure 1. D. maidis nymph (left) and adult (right).
Injury and Crop Impact
- Corn leafhopper can damage corn in two ways – through feeding on the plant and by transmitting plant pathogens.
- Leafhoppers are piercing-sucking insects that feed on plant sap.
- Feeding by large populations of leafhoppers can cause leaf tissue to dry out and eventually die.
- Honeydew excreted by both the adults and nymphs as they feed can lead to sooty mold growth, which can reduce the photosynthetic capacity of the plant.
- Direct plant damage caused by corn leafhopper feeding is rarely significant – the primary economic importance of the corn leafhopper is its role as a disease vector.
- Corn leafhoppers are a vector for Spiroplasma kunkelii, a bacterial pathogen commonly referred to as corn stunt spiroplasma (CSS), which is the primary causal organism for corn stunt disease.
- S. kunkelii is transmitted by corn leafhoppers, which acquire the pathogen by feeding on infected plants and spread it as they subsequently feed on healthy plants.
- This bacterial pathogen is transmitted singly or in combination with maize bushy stunt phytoplasma (MBSP), maize rayado fino virus (MRFV), and/or sugarcane mosaic virus.
Figure 2. Adult corn leafhoppers (D. maidis) on a corn leaf.
Host Species
- D. maidis has a limited host range, feeding only on corn, its wild relatives in the genus Zea and grasses in the closely related genus Tripsacum.
- A Corteva Agriscience study of potential alternate hosts – including sorghum, sugarcane, johnsongrass, pearl millet, soybean, and several species of pasture grass – found that corn was the only host plant on which leafhopper reproduction occurred.
- Other grass crops such as wheat and sorghum, as well as Bermudagrass, can serve as a reservoir for leafhopper populations – giving them a place to persist when no corn is available – but reproduction only occurs on corn.
- Outbreaks of corn stunt in the U.S. are likely driven by leafhopper populations moving up from Mexico, where corn is under continuous cultivation.
Ecology
- Leafhoppers populations can move with prevailing winds, sometimes over long distances.
- Outbreaks of corn stunt disease in southern Florida are believed to have been caused by leafhopper populations carried in with tropical storms.
- The spread of leafhoppers further north into the U.S. is limited by cold temperatures and lack of secondary hosts to provide a year-round source of food.
- Temperature has a significant influence on corn leafhopper development and reproduction. D. maidis requires 648 degree-days above a threshold of 41°F (4.9°C) to complete its lifecycle. • The optimum temperature range for corn leafhopper reproduction is 72 to 77°F (20 to 22°C); at temperatures below this range, reproduction sharply declines.
- The number of corn leafhopper generations per year can vary greatly based on environmental conditions and host availability.
- In the least favorable environments, a minimum of two generations of corn leafhoppers will develop on a single corn crop.
- In areas with favorable temperatures where corn is grown throughout the year – particularly corn under irrigation – corn leafhoppers can go through more than 12 generations per year.
- In areas with year-round corn production, the corn leafhopper maintains breeding populations throughout the year, which can allow populations to grow very large.
Figure 3. A single adult corn leafhopper on a corn leaf.
Management
- Management of corn leafhoppers is primarily focused on preventing the spread of the corn stunt disease pathogens that they carry.
- In the U.S., outbreaks of corn stunt disease have been sporadic, so field experience with managing corn leafhoppers thus far is largely from South America.
- A critical factor for corn leafhopper reproduction is the presence of corn plants on which to feed and reproduce, so cultural control practices are largely focused on eliminating the continuous presence of corn (referred to as a “green bridge”).
- Crop rotation, narrowing the planting window, and controlling volunteer corn are all practices that have been employed to manage corn leafhopper populations.
- Insecticides are commonly used in South America to prevent the spread of corn stunt disease by controlling corn leafhoppers. In Brazil, corn is commonly treated 3 to 6 times per crop for control of corn leafhoppers.
- Corn hybrids can differ in their resistance to corn leafhopper feeding and resistant hybrids have been an important tool for management of corn stunt disease in South America.
- Given the infrequency of corn stunt outbreaks in the U.S., leafhopper resistance ratings have not been developed for U.S. corn hybrids.
- Corn leafhoppers need warm temperatures and a living host for survival and reproduction, which keeps their range in the U.S. largely confined to the southernmost corn production areas.
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