Empoasca fabae

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]