@richluscThu 22 Jun 2023 02.00 EDTLast modified on Sun 25 Jun 2023 09.38 EDT
An invasion of giant African land snails has alarmed residents in south Florida, where authorities have established a quarantine area to try to deal with the destructive pests.
The invasive snails have voracious appetites and consume at least 500 species of plants, according to Florida’s department of agriculture, which is fearful for the state’s lucrative growing industries of citrus and other fruits and vegetables.
In response, it has set up a “treatment area” covering several dozen blocks of the city of Miramar, south-west of Fort Lauderdale, and is warning residents that the slimy creatures also pose a serious health risk to humans by carrying the rat lungworm parasite, known to cause meningitis.
Under the quarantine order, the department says it is unlawful “to move a giant African land snail or a regulated article, including, but not limited to, plants, plant parts, plants in soil, soil, yard waste, debris, compost or building materials”.
It intends to spray the area with the chemical snail bait metaldehyde, which is approved for residential use.
The snails are illegal to import or possess in the US without a permit, and authorities have been trying for years to eradicate them. They can damage buildings, as well as destroying crops, and in some quarters are even considered a delicacy.
In March, customs officers in Detroit intercepted a traveler from Ghana trying to smuggle six snails into the country in a suitcase.
In one of the biggest outbreaks, officials in Miami-Dade discovered almost 150,000 snails in more than two dozen separate areas of the county in 2014, many clinging to houses, eating plaster and stucco to gain calcium for their shells, and eating their way through gardens.
Invasions have occurred in other areas of Florida on an almost annual basis since. Pasco county was placed under quarantine last June after more than a thousand of the snails, which can produce up to 2,500 eggs a year, were discovered in New Port Richey.
Experts believe the snails first arrived in Miami in 1966, and numbers swelled to almost 18,000 within six years. According to an ABC News report, the species was declared eradicated twice in Florida, in 1975, and again in 2021.
“The primary danger is that they’re voracious plant eaters, so they can do an awful lot of damage to both landscapes and to agriculture,” the University of Florida entomologist William Kern told Miami’s Local 10 news station.
“If the snails crawl on uncooked vegetables, you can have a problem with it getting a human infection. With any invasive species, if you find it early, you may be able to control it or eliminate it.”
This article was amended on 24 June 2023 to remove a reference to “female” giant African land snails; they are hermaphroditic, having both male and female reproductive organs.
USDA Agricultural Research Service sent this bulletin at 06/21/2023 09:30 AM EDT
View as a webpageARS News Service The first of two apiaries, established in 2014 in Stoneville, Mississippi, provided honey bees for studying the impact of pesticides on honey bees. (Photo by Yu-Cheng Zhu, D5121-1) Varroa Mites and Deformed Wing Virus Make Honeybees More Susceptible to Insecticides For media inquiries contact: Jessica Ryan, (301) 892-0085 June 21, 2023 Controlling for Varroa mites, the parasitic mites that feed on honey bees and serve as vectors for viral diseases like deformed wing virus (DWV), can help with improving honeybee populations and make bees less susceptible to harmful insecticides, according to a recent study published in Environmental Pollution. Foraging honey bees may be directly exposed to toxic insecticide sprays in the field or exposure may come from honeybees collecting and bringing pesticide-contaminated pollen and nectar back to their hives to feed larvae and young bees. The presence of insecticides, along with other environmental stressors in agricultural areas, can be a factor leading to issues like colony loss — something beekeepers from around the world are trying to overcome. “Previous research has shown how chemicals like pesticides make bees more susceptible to mites,” said Yu-Cheng Zhu, a research entomologist at ARS’s Pollinator Health in Southern Crop Ecosystems Research Unit in Stoneville, Mississippi. “In our study, we wanted to see if mites and viral infestations make bees more susceptible to insecticides.” In a study, researchers with the U.S. Department of Agriculture (USDA)’s Agricultural Research Service (ARS) applied the miticide amitraz (Apivar), a product commonly used for treating Varroa mites, off-label to four bee hives and left the other four hives untreated. They monitored the mite population density monthly and DWV density in early, middle, and late season. Researchers collected bees from miticide-treated and untreated hives, and quantified gene expressions of four immune genes and two physiology-related genes. They also tested bees’ sensitivity to five representative insecticides. In addition, bees’ natural mortalities were recorded during three seasons. “Miticide treatment led to minor or undetectable mite and DWV infestations during the whole bee season, while untreated colonies had substantially higher mite and DWV infestations,” said Zhu. The data analyses showed that Varroa mite population irregularly fluctuated over the bee season and mite population density was not dynamically or closely correlated with the seasonal shift of honey bee natural mortality. Unlike mites, DWV density in untreated colonies progressively increased over the bee season. The density was highly correlated with the seasonal increase in honey bee natural mortality. “In the untreated hives, the increased DWV infestations resulted in decreased physiological and immunity-related functions in late-season honey bees, making the bees more susceptible to insecticides and increasing natural morality rates during the season,” said Zhu. According to Zhu, Varroa mites, also known as Varroa destructor, can reduce fat body and body fluids that contain important detoxification enzymes and immune proteins in honey bees. As a result, bees have impaired immune, detoxification/defense systems, and other essential processes. Coupling those impairments with exposure to insecticides can be detrimental to bee populations. “Having impaired immunity, especially later in the season with fewer food sources, can be challenging for honey bees,” said Zhu. Zhu, whose work focuses on the toxicological impact of pesticides on beneficial insects in the Mississippi Delta Area, said that the study’s results indicated the importance of studying the “bottom-up” effects of mite infestations on the overall health of honey bees in real-world contexts. “Chemical control is still a major method in preventing crop loss and controlling insect pest populations,” said Zhu. “It is important to study the effects of chemical control in honey bee populations so we can find best practices for protecting the health of bees.” The Agricultural Research Service is the U.S. Department of Agriculture’s chief scientific in-house research agency. Daily, ARS focuses on solutions to agricultural problems affecting America. Each dollar invested in U.S. agricultural research results in $20 of economic impact. Interested in reading more about ARS research? Visit our news archive U.S. DEPARTMENT OF AGRICULTURE Agricultural Research Service
Scale insects are a diverse group of small, sap-sucking insects with flat or domed shells. Their lack of mobility and protective shell make them difficult to manage. This explains why many scale species are commercial agricultural pests. Scales pierce plant tissue with their mouthparts to feed on the sap weakening the plant. Any excess fluid is secreted as honeydew, a sticky liquid which is often colonised by sooty mould (Ascomycete fungi species).
Cottony cushion scale (Icerya purchasi) on a Trident maple (Acer buergerianum) branch in Fremont, California. Photo by: Derell Licht (Flickr).
Pests of fruit trees
There are over 8000 described scale insect species. They are small, herbivorous, sap-sucking insects with extreme sexual dimorphism (there are vast differences between males and females). Females tend to be soft-bodied with no limbs and are protected by a domed shell. Males are more like flies, with legs and sometimes wings.
Some scale species are serious commercial pests, particularly of nut and fruit trees. A few examples include:
Red scale (Aonidiella aurantia) is a severe pest of citrus in the USA, Southern Africa, Australia and New Zealand, Mexico, much of South America, Israel and the eastern Mediterranean.
Native to Australia, the Cottony cushion scale (Icerya purchasi) has become widely spread throughout most of the tropical and sub-tropical countries of the world. It has also become established in southern Europe. It is a pest of citrus as well as other fruit and ornamental trees.
The San José scale insect (Diaspidiotus perniciosus) is a pest of several fruit tree species, including peach, pear, apple and plum. This species originates from eastern Asia but has spread to North and South America, New Zealand and northern Europe.
Management of scale insects: Prevention
To prevent initial infestations, purchasing certified nursery stock that is free of scales is very important.
Maintaining natural predator populations is vital for preventing scale populations from reaching a stage where they are causing significant damage. The most important natural enemies (or predators) of scale insects are ladybird beetlesand green lacewings. The main parasitoids of scale insects are chalcidoid wasps. To maintain these populations, avoid using broad-spectrum insecticides and intercrop or plant attractive flowering plants to improve diversity.
In addition, ants protect scales from their natural enemies, so maintaining their local population is imperative. Removing weeds from between trees or planting ant-repellent plants like mint and cinnamon can help to reduce the ant population.
To prevent spreading scales further, clean equipment with water and check clothing before moving between areas with and without scale infestations.
Female scales only tend to move very short distances during their lives. Pruning annually can help to prevent trees from touching and therefore reduces tree-to-tree spread of scales. And when pruning, burn or bury the diseased and dried branches.
Maintaining healthy plants helps to reduce their susceptibility to scale damage. Using recommended fertilizer rates and irrigation schedules is important to keep trees as healthy as possible.
Carpenter ants (Camponotus spp.) tending scale insects in Virginia, USA. Photo by: Judy Gallagher (Flickr).
Management of scale insects: Symptoms
Due to their small size and often cryptic behaviours, they can be difficult to observe until they cause significant damage.
Scale insects tend to attack young shoots and fruits of fruit trees. Particularly citrus, apple, peach, pear and plum species. The plant generally becomes weaker with fewer leaves and buds, and honeydew can form a crust on branches and stems. Although these are the generic symptoms caused by scale insects, there is some variation depending on the species. For example:
Symptoms of red scale: yellow halos around scales’ feeding points and excreted honeydew. Heavy infestations can cause leaves to wilt and fall prematurely, dieback of twigs and branches, deformed and dropped fruits, and stunted growth in young trees.
Symptoms of cottony cushion scale: large quantities of honeydew, fruit drop, wilting leaves, defoliation, and dieback of twigs and small branches.
Symptoms of San José scale: red spots on the fruit (known as ‘chilindrina’), yellowing of the leaves and defoliation. Heavy infestations can cause branches to die and the tree to lose its vigour.
Management of scale insects: Monitoring
To monitor for scale insects during the dormant season, observe fruit trees every week. Look for the presence of scales, black sooty mould growing on excreted honeydew or small holes caused by parasitoids. Inspect approximately 5 trees per hectare, checking 5-10 twigs or branches per tree. If more than 5-10% of the sampled trees are infested, take direct control measures.
During the growing season, monitor for the movement of winged males and parasitoids using sticky traps or pheromone traps. Also, monitor weekly for the symptoms previously mentioned.
Management of scale insects: Direct control
Insecticides tend to be ineffective due to scales’ shell and waxy covering. Instead, mineral oil in contact with the scales’ shell prevents the insect from breathing and it dies. Mineral oil, like Triona 5, should be applied at the beginning of the cycle. Trees are sensitive to the oil, and if applied when plants are sprouting, flowering or fruiting, the fruit or flowers may fall. Follow the instructions on the label of the product.
There are several types of species which can be used for biocontrol of scale insects. Check with the Ministry of Agriculture in your country for local recommendations for biocontrol and consider advice from local extension officers. In tropical regions, parasitic wasps like Metaphycus luteolus and parasites like Aphytis lignanensis can be successful when released locally. Whereas in temperate conditions, A. melinus may be more suitable. Finally, in arid and hot inland areas where insecticides aren’t over-used, the Vedalia beetle (Novius cardinalis) is commonly used.
Ant populations should be controlled to prevent them from protecting scales from their natural enemies. Sticky barriers around tree trunks can be created using duct tape or fabric tree wrap coated with a sticky substance like Tanglefoot on infested trees. Double-sided sticky tape can also be used on branches. The barriers should be checked every week or two, and any debris that builds up should be removed to prevent ants from crossing the barrier.
During the summer, remove any infested branches, leaves or fruit to isolate the damage. Burn the infested plant material, or bury it at least 20cm deep.
Further reading
If you would like to find more information on this subject, please see the links below:
For a wide range of resources relating to scale insects, including country and species-specific information, try this PlantwisePlus Knowledge Bank search
The samurai wasp (Trissolcus japonicus) is a tiny parasitoid that attacks the eggs of the brown marmorated stink bug (Halyomorpha halys), a notorious pest that damages fruit and vegetable crops around the world.
The wasp lays its eggs inside the stink bug eggs, killing them and producing more wasps.
The samurai wasp is native to Asia, where it co-evolved with the stink bug and helps to keep its population in check.
The samurai wasp has been introduced or detected in several countries where the stink bug has invaded, such as the United States, Canada, Switzerland, Italy, and Germany.
It is considered a promising biological control agent that can reduce stink bug damage and pesticide use.
However, there are also concerns about its potential impact on native stink bugs that are not pests and may have ecological or economic value.
A new study led by CABI has investigated the host range and specificity of the samurai wasp in Europe, where it has been accidentally or intentionally released in recent years.
The study aimed to assess how likely the wasp is to attack and parasitize native stink bugs in the field, and what factors may influence its host selection.
The methods and results of the study (Photo : GUILLAUME SOUVANT/AFP via Getty Images)
The study, published in the Journal of Pest Science, involved exposing sentinel egg masses of the stink bug and 18 non-target species to the samurai wasp in Switzerland and Italy over three years, as per Phys.org.
The researchers also collected naturally laid egg masses from different habitats and locations.
They then analyzed the parasitism rates and patterns of each species by the wasp using molecular and morphological methods.
The results showed that the samurai wasp has a broad fundamental host range, meaning that it can successfully parasitize many species of stink bugs under laboratory conditions.
In fact, 15 of 18 non-target species were parasitized by the wasp in the field.
However, most non-target species were less parasitized than the stink bug, suggesting that they have partial temporal or spatial refuges from the wasp attack.
The researchers found that the realized host range of the samurai wasp, meaning the actual hosts that it attacks and parasitizes in nature, depends on several factors, such as:
The availability and abundance of hosts. The wasp tends to prefer hosts that are more common and accessible in its environment.
The phenology and life cycle of hosts. The wasp tends to prefer hosts that lay their eggs at the same time as the stink bug or later in the season when its population is higher.
The ecological niche and habitat of hosts. The wasp tends to prefer hosts that share similar habitats and resources with the stink bug, such as fruit trees or crops.
The phylogenetic relatedness of hosts. The wasp tends to prefer hosts that are more closely related to the stink bug, such as other members of the Pentatomidae family.
The implications and recommendations for conservation and management
The study confirmed that the samurai wasp has minimal impact on native stink bugs in Europe, as it mainly targets its primary host, the stink bug, as per CABI News.
However, it also revealed that some non-target species may face an increased risk of parasitism by the wasp, especially those that have an unusual life cycle or occupy the same ecological niche as the stink bug.
For example, Pentatoma rufipes, a native species that feed on fruits and seeds, was the most parasitized non-target species in both countries.
The researchers recommend that more studies be done to evaluate the impact of non-target parasitism on the population dynamics and fitness of native stink bugs.
They also suggest that more monitoring and surveillance be done to track the distribution and abundance of both the samurai wasp and its hosts across different regions and habitats.
They also urge caution and coordination when releasing or managing the samurai wasp, as it may have different effects in different contexts.
The samurai wasp is a valuable ally in the fight against the stink bug, but it is not a silver bullet.
It is important to consider its potential benefits and risks for the native biodiversity and ecosystem services and to adopt an integrated pest management approach that combines biological, cultural, and chemical methods.
PlantVillage, a Penn State-sponsored project through its mobile application is helping cassava and maize farmers from Western Kenya to scan and analyse diseases, by satellite data, affecting their crops and take immediate, proper remedy actions.
This comes at a time research by Masinde Muliro University of Science and Technology, one of the higher learning institutions in the region, indicates that Western Kenya is one of the food baskets of the country but crop yields have remained far much below the world averages mainly due to pests and disease.
However, PlantVillage comes in handy by using artificial intelligence and satellite data to effectively inform even the smallholder farmers on the danger approaching and be able to make the best decision on how to approach it.
All a farmer needs to do is point a smartphone with the app at a diseased plant, and artificial intelligence will analyze the leaves and tell out exactly what has gone awry so that the farmer can appropriately remedy the situation.
“If the plant is not doing well, then the farmer has to do something very different from what has been done before, either apply a pesticide, plant a different crop, or start irrigating,” said David Hughes, Penn State biologist, and the app developer.
Past information
The satellite data also reaches years into the past, so the farmers can see how well their plants are performing historically. On top of that, they can compare their performance with their neighbors. Meaning, maybe it’s not a rainfall problem but a pest problem that’s holding their crops back.
The researchers have been testing the new system in Western Kenya, handing out phones to ‘lead’ farmers, who travel around the community bringing insight to their neighbors.
“We’re able to tell them they have a problem, and with the AI assistant go into the field and see if that problem is a disease that’s causing a decrease in the yield or it’s actually drought,” said Hughes.
With this satellite data, though, farmers can react before it’s too late.
In addition to the detective work, the app is gaining new powers thanks to eyes in the sky. Using free satellite data from the UN, PlantVillage can monitor biomass on a plot of land, giving small-scale farmers insight into how their crops are developing.
$4.96 million grant
Last month PlantVillage received an award grant of $4.96 million grant from Bill & Melinda Gates Foundation to help increase food production for smallholder farmers who face pests and disease of their crops across sub-Saharan Africa.
Through a research project called Delphi, PlantVillage was to create a modeling platform that can be used by researchers globally to improve the speed and accuracy of efforts to identify emerging threats.
The United Nations Food and Agriculture Organization (FAO) estimates that each year, 20% to 40% of global crop production is lost to plant pests and diseases. The global economic cost of plant diseases alone is estimated to be $220 billion, and invasive insects account for an additional $70 billion in losses.
The first of two apiaries, established in 2014 in Stoneville, Mississippi, provided honey bees for studying the impact of pesticides on honey bees. (Photo by Yu-Cheng Zhu, D5121-1) Varroa Mites and Deformed Wing Virus Make Honeybees More Susceptible to Insecticides For media inquiries contact: 
