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Are you interested in keeping up to date with crop pest and disease literature reports? You’re invited to sign up to our monthly pest alert email containing links to recently published scientific literature from around the globe. On sign up, select which country or region you are interested in, or the Worldwide regional option. Feel […]

via Plantwise Pest Alerts – free email subscription service — The Plantwise Blog

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Insecticides being sprayed on coffee plants in Uganda, a country with endemic schistosomiasis. 

REUTERS/Hereward Holland

Pesticides could hike risk of catching a parasitic worm

Pesticides are a double-edged sword: They make farming more productive, but they can harm wildlife and people if not used properly. Now, ecologists have identified a new threat from pesticides in the developing world. By killing off insect predators of worm-infested snails, they can raise the risk of schistosomiasis, the second most common parasitic disease after malaria.

“It’s a ground-breaking article,” says Russell Stothard, a parasitologist at the Liverpool School of Tropical Medicine in the United Kingdom, who was not involved in the research.

Schistosomiasis is a debilitating disease caused by a parasitic flatworm. Some 258 million people are infected, mostly in Africa. The worm spends part of its life in freshwater snails, which release larvae that can penetrate the skin of someone swimming, bathing, or washing clothes. The centimeter-long worms spread through blood vessels, causing fever, diarrhea, anemia, and stunted growth. Immune responses can damage the kidneys and other organs. When infected people relive themselves, the worms’ eggs can spread into streams or ponds via their urine and feces. There, they hatch and seek out new snails, beginning their life cycle again. Schistosomiasis can easily be treated with drugs, but where the parasites are endemic, people quickly become reinfected.

The leader of the new research, ecologist Jason Rohr of the University of South Florida in Tampa, had previously studied a similar parasitic flatworm in amphibians. His research showed that common agricultural chemicals, like fertilizer, can worsen the situation for frogs. When these chemicals enter streams and ponds, they increase the amount of algae, which is then eaten by snails that serve as a host for the flatworms. That boosts their population and leads to more parasite infections in frogs.

The similar life cycles of the amphibian flatworm and the one that causes schistosomiasis made Rohr and his colleagues wonder whether agricultural pollution might also affect disease transmission. They created a simple ecological model inside 60 open tanks. After filling each with 800 liters of pond water, they added two species of snails that spread the schistosomiasis parasite, algae for the snails to eat, and two kinds of predators—crayfish and water bugs. Finally, they spiked the tanks with three kinds of farm chemicals—fertilizer, herbicide, and insecticide—in various combinations. The concentrations were typical of streams and ponds near corn fields in the United States.

As expected, fertilizer increased the amount of algae in the tanks, which in turn swelled the number of snails. The herbicide also led to more food for the snails, because it predominately killed microscopic algae that clouded the water. When these died, the water cleared, allowing more light to reach larger algae growing on the bottom of the pond—the snails’ food. An epidemiological model of schistosomiasis suggested that the increase in snail population from this typical amount of fertilizer would jack up the risk of transmission to humans by 28%.

The insecticide, chlorpyrifos, had an even bigger effect by killing the two predators of the snails. Water bugs stick their heads inside the shell, bite the mollusc, inject digestive enzymes, then slurp up the remains. The 20-centimeter-long crayfish rely on brute force, crushing the 2-centimeter-long snails. “They’re absolutely voracious,” Rohr says. With these predators gone, the snail population exploded. In such a scenario, disease risk to humans would rise 10-fold, the team reports in a preprint posted this week to bioRxiv. Although only one concentration of insecticide was added to the tanks, the model indicated that lower concentrations in ponds would still have substantial impacts on parasite transmission.

The findings identify what looks like a “strong risk factor” for schistosomiasis, says Joanne Webster, a parasitologist at Imperial College London who was not involved.

Dams have also caused an increase in schistosomiasis in many countries, because snails live in the reservoirs and irrigation channels. In some places, dams have also caused a decline in the natural predators of snails, such as fish, crayfish, and prawns. The combination of new habitat from irrigation and runoff of pesticides may be a “perfect storm” for schistosomiasis where agriculture is intensifying in the developing world, Rohr says.

Rohr is now investigating the impact of insecticides on snail predators and disease transmission in northwest Senegal, as part of an experiment run by a research partnership called the Upstream Alliance, based in Pacific Grove, California. This project has reintroduced prawns near several villages to evaluate their efficacy in controlling freshwater snails. Rohr will study whether helping farmers switch to insecticides less toxic to prawns could lessen the burden of schistosomiasis, while maintaining food production. “In schistosomiasis-endemic regions, we need to think more carefully about the impact of agrochemicals,” he says.

The study highlights the complex links between agriculture and disease, says Charles Godfray, a biologist at the University of Oxford in the United Kingdom. By boosting agricultural productivity, pesticides and other chemicals can help raise people out of poverty and lessen malnutrition, which worsens diseases. “The really clear thing is the importance of precision agriculture, in which agrochemicals are used as efficiently as possible, with as little runoff as possible.”

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ScienceAdvances

Climate warming promotes species diversity, but with greater taxonomic redundancy, in complex environments2

Abstract

Climate warming is predicted to alter species interactions, which could potentially lead to extinction events. However, there is an ongoing debate whether the effects of warming on biodiversity may be moderated by biodiversity itself. We tested warming effects on soil nematodes, one of the most diverse and abundant metazoans in terrestrial ecosystems, along a gradient of environmental complexity created by a gradient of plant species richness. Warming increased nematode species diversity in complex (16-species mixtures) plant communities (by ~36%) but decreased it in simple (monocultures) plant communities (by ~39%) compared to ambient temperature. Further, warming led to higher levels of taxonomic relatedness in nematode communities across all levels of plant species richness. Our results highlight both the need for maintaining species-rich plant communities to help offset detrimental warming effects and the inability of species-rich plant communities to maintain nematode taxonomic distinctness when warming occur.

This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial license, which permits use, distribution, and reproduction in any medium, so long as the resultant use is not for commercial advantage and provided the original work is properly cited.

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FAO

Ethiopia intensifies efforts to battle the fall armyworm
30/05/2017

In collaboration with the Food and Agriculture Organization of the United Nations (FAO) and other development partners, the Government of Ethiopia has intensified efforts to protect major maize growing areas from the ravage of the fall armyworm. The fall armyworm, which first arrived in Africa in 2016, was intercepted on a few hectares of irrigated maize fields in southern Ethiopia in the last week of February 2017. It has now covered about 52 962 hectares in 144 districts in three of the major maize-growing regional states – Gambella, Oromia and Southern Nations Nationalities and Peoples’ Region (SNNPR).

Tazelekew Habtamu, a maize farmer in southern Ethiopia where the insect set foot for the first time in Ethiopia, observed unusual insect pest infestation on his maize farm in the first week of March 2017. He reported the case to a local agriculture extension worker, who facilitated immediate pesticide spraying. “At first, the fall armyworm infestation was huge,” said Tazelekew. “The pesticide spray killed most of the pests. I would have lost my maize plants if I did not use the pesticide. However, some remnants of the fall armyworm are still attacking my maize field.”

The fall armyworm is a migratory insect pest known to cause massive destruction of maize crops under warm and humid conditions in the Americans. In Ethiopia, maize fields planted in belg and meher seasons in the prevailing warm and moist weather conditions provide favorable environment for the insect to multiply massively and spread to more areas. “The weather conditions from March to September in maize growing areas provide fertile ground for the insect to mass multiply and spread easily,” said Zebdewos Salato, Director of the Plant Protection Directorate at the Ethiopian Ministry of Agriculture and Natural Resources. Aided by wind front, the fall armyworm of a single generation can spread quickly as far as 500 km away from its point of emergence.

“We expect the infestation to spread to other regions and cover wider areas in the coming months,” he said. “Many farmers in the regions have already planted maize or will plant in June. As more areas plant maize  it is very likely that the pests will spread to more maize areas including in Afar, Amhara, Benishangul Gumz, Oromia and Tigray. We are working hard to make vulnerable regions aware of the need to prepare for possible fall armyworm infestation.”

“The insect is establishing itself and is expected to remain an economic pest for very long time to come hence we need to put in place a short and long term fall armyworm management and control plan,” said Bayeh Mulatu, National Integrated Pest Management Expert at FAO Ethiopia.

For the current season, pesticides have been recommended, as the infestation is massive. Farmers are being advised to handpick the insect when the infestations are very low or apply contact and systemic pesticides using knapsack sprayers when the infestation is significant to cause economic damage, he said.

Farmers are informed to undertake routine monitoring of their farms and exercise handpicking of larvae, which escape the pesticide. According to recent reports, about 24 000 hectares of maize fields have been sprayed with about 36 000 litres of pesticides, and about 12 600 hectares of land have been covered by handpicking the fall armyworm.

However, the control effort has its own challenge. The Government of Ethiopia allocated nearly USD 2 million to tackle the problem. “With this resource, we purchased pesticide and managed to cover only 44 percent of the total maize field so far infested by the fall armyworm,” Zebdewos said. “Taking into consideration the growing infestation of the insect in the wider regions and the below 50 percent infested are treated using pesticides, it would be a big challenge for the Ethiopian Government to address the problem fully. We have challenges with in carrying out effective fall armyworm monitoring, supply of safety outfits, working spraying equipment and other logistics.” According to Zebdewos, even if the control activities are progressing, the impacts of the pest infestation will negatively affect the production of maize in this year, as it takes time for the affected plants to recover.

The Africa wide meeting on the fall armyworm that was held in Nairobi, Kenya gave the responsibility to FAO to coordinate interventions to bring the fall armyworm problem under control. In addition to funding of USD 52 000, FAO supports the Government’s prevention efforts with expert advice and consultation, and facilitation of field assessments, surveillance and monitoring. In addition, in collaboration with the Desert Locust Control Organization for Eastern Africa (DLCO-EA) and other development partners, FAO is developing a project to derail the insect expansion and mass multiplication so that yield loss could be minimized significantly.

In Ethiopia, about nine million smallholder farmers grow maize on 2 million hectares of land, and 75 percent of the maize produced is consumed family as food. Dry stock is mainly used for animal feed and part as fuel and the rest left to decay and amend soil. Amadou Allahoury, FAO Representative in Ethiopia said, “Millions of Ethiopian farmers rely on maize crop as staple food. The livelihood of these smallholder farmers will be at stake if the threat of the pest is not foiled. As FAO, we will continue providing the needed support to the Government in its efforts to tackle the problem.”

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Huanglongbing (HLB), also known as Citrus greening, has been confirmed in Trinidad for the first time. The disease, which was detected on leaves from a lime tree in the north of the island, can cause devastating yield loss for Citrus growers and is regarded as one of the most important threats to global commercial and […]

via Citrus greening detected in Trinidad — The Plantwise Blog

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SE farm press

HLB-citrus greening disease confirmed in Alabama

HLB was found in leaf and insect samples from a residential property on Dauphin Island in Mobile County.

Cary Blake 1 | Jun 22, 2017

The feared citrus disease Huanglongbing (HLB) – a.k.a. citrus greening – has been confirmed in Alabama, according to the state’s Department of Agriculture and Industries (ADAI).

HLB was found in leaf and insect samples from a residential property on Dauphin Island in Mobile County. Dauphin Island is a town located on a barrier island with the same name at the Gulf of Mexico.

 Federal and state officials confirmed the major citrus disease, caused by the bacterial pathogen Candidatus Liberibacter asiaticus vectored by the Asian citrus psyllid pest.

The ADAI, USDA’s Animal Plant Health Inspection Service, and the U.S. Department of Homeland Security Customs and Border Protection will conduct a delimiting survey to determine the extent the pathogen’s spread.

If the disease is limited to only a few trees, steps will be taken to eradicate the disease.

Meanwhile, ADAI says officials have begun the process to halt citrus plant movement from the area. Federal plant officials will seek to establish a citrus greening quarantine in Mobile County.

Alabama agriculture officials say the state intends to take action to establish a parallel quarantine. The dual action makes it possible for federal regulators to hold the quarantine only in Mobile County where the disease has been confirmed.

Florida, for decades the largest citrus-producing state for juice in the nation, was the first U.S. state where HLB was found (2005). Due to HLB-caused tree death and related factors, some estimates suggest that HLB has eliminated 75 percent of Florida’s citrus industry.

Nearly 40 HLB positive finds have been found in California, all in urban areas in residential areas with no finds in commercial citrus. Most California citrus is sold for the fresh market.

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