UK Frog Populations

Science (Oct. 8, 2010) — Common frog (Rana temporaria) populations across the UK are suffering dramatic population crashes due to infection from the emerging disease Ranavirus, reveals research published in the Zoological Society of London’s (ZSL) journal Animal Conservation.

Using data collected from the public by the Frog Mortality Project and Froglife, scientists from ZSL found that, on average, infected frog populations experienced an 81 per cent decline in adult frogs over a 12 year period.

“Our findings show that Ranavirus not only causes one-off mass-mortality events, but is also responsible for long-term population declines. We need to understand more about this virus if we are to minimise the serious threat that it poses to our native amphibians,” says Dr Amber Teacher, lead author from ZSL.

Despite a number of populations suffering from infection year-on-year, other populations bounced-back from mass-mortality events. This suggests that some frogs may have some form of immunity to ranaviral infection.

“The discovery of persistent populations in the face of disease emergence is very encouraging and offers hope for the long-term future of this species” says Lucy Benyon, Froglife. “However, we still need regular information from the public on what is happening in their ponds to continue this essential research.”

In the 80s and 90s, the disease was particularly associated with the southeast of England. In recent years new ‘pockets’ of diseases have turned up in Lancashire, Yorkshire and along the south coast.

“It is very difficult to treat wildlife diseases and so the mystery that we desperately need to solve is how the disease spreads. Understanding more about the ecology of the disease will allow us to offer advice to the public on how to limit the spread of infection, which could also prevent the movement of other frog diseases in the future,” says co-author Dr Trent Garner from ZSL.

Sourced & published by Henry Sapiecha

Science (July 17, 2010) — In the battle between insect predators and their prey, chemical signals called kairomones serve as an early-warning system. Pervasively emitted by the predators, the compounds are detected by their prey, and can even trigger adaptations, such a change in body size or armor, that help protect the prey. But as widespread as kairomones are in the insect world, their chemical identity has remained largely unknown. New research by Rockefeller University’s Joel E. Cohen and colleagues at the University of Haifa in Israel has identified two compounds emitted by mosquito predators that make the mosquitoes less inclined to lay eggs in pools of water.

The findings, published in the July issue of Ecology Letters, may provide new environmentally friendly tactics for repelling and controlling disease-carrying insects.

Many animals use chemicals to communicate with each other. Pheromones, which influence social and reproductive behaviors within a particular species, are probably the best known and studied. Kairomones are produced by an individual of one species and received by an individual of a different species, with the receiving species often benefiting at the expense of the donor.

Cohen and his Israeli colleagues focused on the interaction between two insect species found in temporary pools of the Mediterranean and the Middle East: larvae of the mosquito C. longiareolata and its predator, the backswimmer N. maculata. When the arriving female mosquitoes detect a chemical emitted by the backswimmer, they are less likely to lay eggs in that pool.

To reproduce conditions of temporary pools in the field, the researchers used aged tap water with fish food added as a source of nutrients. Individual backswimmers were then placed in vials containing samples of the temporary pools, and air samples were collected from the headspace within the vials. The researchers used gas chromatography-mass spectrometry to analyze the chemicals emitted by the backswimmers.

Cohen and his colleagues identified two chemicals, hydrocarbons called n-heneicosane and n-tricosane, which repelled egg-laying by mosquitoes at the concentrations of those compounds found in nature. Together, the two chemicals had an additive effect.

Since the mosquitoes can detect the backswimmer’s kairomones from above the water’s surface, predator-released kairomones can reduce the mosquito’s immediate risk of predation, says Cohen. But they also increase the female mosquito’s chance of dying from other causes before she finds a pool safe for her to lay her eggs in.

“That’s why we think these chemicals could be a useful part of a strategy to control the population size of mosquitoes,” says Cohen, who is the Abby Mauzé Rockefeller Professor and head of the Laboratory of Populations. “We started this work from very basic curiosity about how food webs and predator-prey interactions work, but we now see unexpected practical applications. These newly identified compounds, and others that remain to be discovered, might be effective in controlling populations of disease-carrying insects. It’s far too soon to say, but there’s the possibility of an advance in the battle against infectious disease.”

Sourced & published by Henry Sapiecha

from Predators:

Researchers Look for

Small Control Organism

Science (June 21, 2010) — One way to keep from getting eaten is to run. But recent research at the University of Guam’s Western Pacific Tropical Research Center shows that sometimes it’s better to just hide.

“The small size of an alien insect that feeds on a native tree from the western Pacific island of Guam allows it to hide in cracks and other locations that are out of reach for its only local natural enemy,” said UOG entomologist Aubrey Moore.

Moore has teamed up with UOG ecologist Thomas Marler to study the relationship between the native cycad tree, known as “fadang” in the Chamorro language, and a minute alien insect pest called cycad aulacaspis scale (CAS). The pest arrived on Guam in 2003, and then spread to Rota 50 miles north and Palau 800 miles southwest of Guam. The pest has killed 90% of Guam’s wild cycads. Findings about the ability of CAS to go undetected in secretive locations on cycad plants were published by Marler and Moore in the May issue of the journal HortScience.

The researchers have been interested in using biological control efforts to save the native fadang populations on Guam, Rota, and Palau. A predatory lady beetle that feeds on CAS was introduced to the three islands to control the pest. “Our initial Guam release was in early 2005 and the beetle established quickly and appeared to be doing a good job of controlling the scale insects by preying on them,” said Moore. But then a second epidemic outbreak of the scale pest occurred in late 2008 on Guam and early 2010 on Rota. Ecologists call this type of population behavior an “irruption” and it was this secondary increase in the pest population that caught the attention of the researchers.

“We wanted to know how the insect pest population could increase to such a serious threat level after the initial threat was brought under reasonable control by the predatory beetle,” said Marler. When some of the tiny insects find a hiding spot where they can feed and make babies without fear of being eaten by the beetle, all it takes for a sudden increase in the pest population is for the beetles to migrate away from the area after they run out of accessible scale insects.

The HortScience article also explains a more insidious outcome of this ability to hide. Cycads are valuable landscaping plants. Many species of cycads are susceptible to the pest, and the out-of-sight crannies on the plants can harbor a few undetectable scale insects. “We believe this is one of the reasons the insect has been so successful in spreading throughout many countries in recent years, as visual inspection of imported plants cannot detect the hiding insects,” said Marler.

Most programs for control of a pest that causes major agricultural or ecological damage do not rely on a single biological control organism. So the Guam team is making plans to introduce a second natural enemy of CAS. They contend that the findings about the secretive nature of the scale pest help inform what sort of natural enemy is needed on Guam and Rota. “Our work has shown that we need to find a biological control organism that is small enough to follow CAS into its tiny hiding places,” concluded Moore.

Sourced and published by Henry Sapiecha