Potato leafhopper

Potato leafhopper
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Order:	Hemiptera
Suborder:	Auchenorrhyncha
Family:	Cicadellidae
Genus:	Empoasca
Species:	E. fabae
Binomial name
Empoasca fabae (Harris, 1841)

Potato leafhopper (Empoasca fabae) belongs to family Cicadellidae and genus Empoasca within order Hemiptera.^[1] In North America they are a serious agricultural pest.^[2] Every year millions of dollars are lost from reduced crop yields and on pest management.^[3] Crops that are impacted the most are potatoes, clover, beans, apples and alfalfa.^[4]

Adults have pale to iridescent green bodies with 6 or 8 white spots on their pronotum.^[4] They have a distinctive white H shape mark between their head and wing base.^[5] Their bodies are approximately 3 mm long and have on their front wings near its tip a crossvein.^[4] Adults and nymphs move by hopping among host plants.^[5] However, only adults can fly.^[6]

They are able to feed and reproduce on at least 200 different plant species across twenty-six families.^[1] In total herb genera represent 64% of their hosts.^[7] Adults prefer to feed on the leaves and stems, while the nymphs prefer the leaves.^[7] Their specialized mouth parts are able to pierce into the plant tissue and remove its sap.^[8] The ability to inhabit a wide range of hosts is due to the variation in their feeding behaviors.^[9]

Empoasca fabae is a seasonal migration species.^[10] If they are flying at night, it takes two or three days to reach their summer destinations.^[11] Research suggests that they are using winds as a passive means to help migrate.^[10] The direction of the winds influence their distribution within their summer range.^[10] Typically, the winds blow in a north-northeast direction towards Northern and Midwest United States.^[10] Factors such as warm temperatures and lack of precipitation increases their range.^[11] Cold temperatures, major precipitation, and unsuitable environmental conditions are factors that will stop migration to continue more north.^[11] In late summer, cold fronts start to appear sending cues for them to leave.^[10] As they leave they get caught up in these fronts which carry them south to southwest to their overwintering range.^[10]

Due to their inability to tolerate the cold winter temperatures they must migrate south.^[10] Adults overwinter on hosts in the pine and mixed hardwood forests along the Gulf of Mexico and in the Southern United States.^[12] Eastern Texas and Oklahoma, Virginia, Louisiana, Florida, Georgia, South and North Carolina, Alabama, Tennessee, Arkansas, and Mississippi, have documented populations.^[12] Before migrating back to their summer range they change their hosts to herbaceous legumes then to new spring foliage of deciduous trees.^[12]

Their summer range extends across the Midwest and eastern parts of Canada and the United States.^[13] In Canada, they are found only in the Great Lakes region.^[10] They are able to inhabit a wide range of habitats.^[9] Only about 32% of individuals actually occupy croplands.^[9] The remaining individuals will reside in fields, woodlands, scrublands, waste places, and parks.^[9] Precipitation will deposit individuals upon plant hosts where they will quickly re-establish themselves.^[14]

Before migrating they mate and enter reproductive diapause.^[12] Empoasca fabae begin to enter into reproductive dispause at the end of July.^[15] The entire population remains in this state for its migration and overwintering period.^[12] This diapause period ends from mid-January through February, and they begin to sexually mature.^[12]

During the spring migration north, the majority of the individuals are females.^[16] When they return if temperatures are above 10 °C they can start oviposition and populations grow and re-establish themselves.^[17] Empoasca fabae arrives back to their summer ranges during April or early May depending on the location.^[18]

During the summer months they can, on average, lay eggs over a span of 96 days.^[19] Peak population densities occur during late May to late June.^[8] Many overlapping generations appear.^[8] After this their population densities begin to decline slowly.^[18] Individuals have a tendency to aggregate as their populations increase.^[18] At the end of the summer, individuals either die or migrate south.^[20]

Eggs are laid on their hosts; they are transparent and small in size.^[5] Females will lay 2 or 3 eggs a day on the plant's stem and leaf veins.^[21] The egg's incubation period ranges from 4 through 23 days, the hatchings are called nymphs.^[19] New hatchlings are white in colour and develop their green colouring as they age.^[19] The nymphs undergo five instars before becoming adults.^[16] As they develop, they lose their skin and develop their wings.^[5] Empoasca fabae develops into adults in 8 through 37 days.^[19] Their entire lifecycle is one month long.^[21]

The visually descriptive term hopperburn is used for a distinct type of damage on plants by E. fabae's feeding on its hosts.^[16] As they feed their saliva mechanically injures the phloem and parenchyma cells.^[2] The plant also suffers damage to its vascular cambium, and to its vascular bundles.^[16] Within 24 hours of being infested, rates of photosynthesis, and transpiration are reduced, leaves accumulate starch, and transport of photoassimilates are reduced.^[7]

The first symptoms of hopperburn is that a leaflet's margins start to curl up.^[7] As a plant's infestation increases, its leaves cup downward, and they start to turn from green to yellow.^[22] In severe infestations this leads to leaf necrosis in which the leaf margins and intervein areas turn brown.^[22] Older plants completely lose their leaves.^[3] Young plants display tip-wilting and will be stunted in height.^[3] Plants that were damaged by stem feeding suffered more damage to their physiologies than those which were damaged by leaf eating.^[7]

Research has shown that water-stressed plants increase nymph's development time.^[6] This causes severe hopperburn due to the increase plant stress response.^[21]

Hopperburn leads to reduced plant growth and reproduction.^[3] In some heavily infested fields up to 75% of the yield is lost, it depends on what stage of development the plants are in.^[13] Obviously, this leads to reductions in crop yields and large economic losses.^[3] For example, in 1988 the losses of alfalfa crops in Northeast United States ranged from $32-$66 per hectare.^[23] The amount of crop damage is directly proportional to the population density.^[13] Most crop damage comes from the future generations of the initial arrivals back to the summer range.^[11]

Research has indicated that over the last 62 years that they have been arriving back to their summer range earlier by ten days.^[24] Warmer temperatures increases the time and speed of egg hatching and nymph development.^[17] There is increasing concern that climate change will shift the overwintering and summer ranges more northward.^[24] This will exacerbate the problem of pest management and increase economic losses. .^[24]

Usually, crop detection of E. fabae is too late as hopperburn is the first visual symptom of a major infestation.^[21] Regular crop inspections with a sweep net are essential to help reduce massive economic losses.^[21] Another visual cue is the death of leaves with small pits holes throughout them resulting from their eggs.^[5] Host expansion is likely caused from the loss of natural resistance through extensive plant breeding.^[1]

Currently, the only effective method that exists for controlling E. fabae's infestations is the heavy application of insecticides.^[13] Short-lived insecticides such as carbaryl are commonly used; however they require costly reapplications.^[14]

Research is indicating the possibility of being able to control populations by increasing E. fabae's natural enemies as part of pest management plan.^[25] Percent mortality has been shown to be highest in individuals in younger instars.^[15] Research has shown that natural resistance and pesticide use are just as effective, but neither is capable to fully contain populations.^[26] To create more effective management programs and reduce pesticide use it is essential to understand their dispersion, temporal and spatial patterns.^[18]