Study uncovers optimal ecology of bioinsecticide

ScienceDaily (May 20, 2010) — BBSRC-funded researchers at the University of Oxford and Royal Holloway University of London have discovered that the commonly used and naturally occurring bacterial insecticide Bt works best if applied to young plants and is enhanced by the presence of the insect pests.



The research is published in the open-access journal PLoS Pathogens.

Spraying Bt -- the bacterium Bacillus thuringiensis -- is a common method for controlling a variety of insect pests and is one of the main approaches to chemical-free pest control in agriculture. Optimising sustainable farming techniques can help meet the challenge of feeding 9 billion people by 2050 using fewer resources and with minimum impact on the environment.

Senior researcher Dr Mike Bonsall at the University of Oxford said: "Bt has been used commercially for about 40 years and is readily available to control pest moths and the like, but until now we've known very little about the natural abundance of the bacteria in the environment and what happens when we apply extra bacteria as a means of pest control. It's really important to understand what is happening so that we can, for example, know what factors might have an impact on the insects becoming resistant to Bt."

Bt is found naturally in soils and on plants and exists as many different varieties that each have a preference for infecting different organisms. Bt strains that are specific to certain insects rely on being able to infect those insects in order to reproduce. The researchers studied a strain called ST8, which infects the Diamondback Moth -- a pest that attacks cabbages, broccoli and related crops -- and they found that the population of bacteria (either existing or applied) establishes itself more readily when the insects are present.

The team set up several cabbage plots in the field to examine what was happening when there were extra insects and/or extra bacteria added to what was already present. Then they took samples of soil and leaves. For each sample they looked at the genetics of the bacteria to build a profile of which strains of Bt were present and in what numbers.

Lead researcher Dr Ben Raymond at Royal Holloway University of London said: "We found that our strain, ST8, is the most common in the environment already and it also seems to be best at getting onto the leaves where it can infect the moths. We think that the ST8 that exists naturally in the farm environment might well be colonising the plant as growing seedlings so it gets the earliest possible opportunity to infect the moths, which of course it needs to do to survive.

"This makes sense given that we also found that when there are extra insects in the environment the bacteria actually do much better and can be found in larger numbers. It also shows why spraying the plants, especially young ones, rather than the soil is the best way of using Bt to control insect pests."

The research team are also looking at factors that affect the chances of insects becoming resistant to Bt. In particular they are looking at the way the toxin that kills the insect and an antibiotic that Bt produces to get rid of competing strains of bacteria in the insect's gut both impact the evolution of resistance in the insect.

Professor Douglas Kell, BBSRC Chief Executive said: "Sustainable solutions to future food security will rely on a thorough understanding of how ecosystems operate. This is a good example where the interactions between different parts of such a system have a significant impact on how we can control pests using biological rather than chemical methods. It is also vital that our ongoing practices with Bt present minimal risk of insects becoming resistant and so work to understand the fundamental biology that happens within this system is extremely important."

Ant Has Given Up Sex Completely, Researchers Confirm

Ant Has Given Up Sex Completely, Researchers Confirm

ScienceDaily (Jan. 9, 2010) — The complete asexuality of a widespread fungus-gardening ant, the only ant species in the world known to have dispensed with males entirely, has been confirmed by a team of Texas and Brazilian researchers.

Most social insects—the wasps, ants and bees—are relatively used to daily life without males. Their colonies are well run by swarms of sterile sisters lorded over by an egg-laying queen. But, eventually, all social insect species have the ability to produce a crop of males who go forth in the world to fertilize new queens and propagate.

Queens of the ant Mycocepurus smithii reproduce without fertilization and males appear to be completely absent, report Christian Rabeling, Ulrich Mueller and their Brazilian colleagues in PLoS ONE this week.

"Animals that are completely asexual are relatively rare, which makes this is a very interesting ant," says Rabeling, an ecology, evolution and behavior graduate student at The University of Texas at Austin. "Asexual species don't mix their genes through recombination, so you expect harmful mutations to accumulate over time and for the species to go extinct more quickly than others. They don't generally persist for very long over evolutionary time."

Previous studies of the ants from Puerto Rico and Panama have pointed toward the ants being completely asexual. One study in particular, by Mueller and former graduate student Anna Himler (now at Arizona State University), showed that the ants reproduced in the lab without males, and that no amount of stress induced the production of males.

Scientists believed that specimens of male ants previously collected in Brazil in the 1960s could be males of M. smithii. If males of the species existed, it would suggest that—at least from time to time—the ants reproduce sexually.

Rabeling analyzed the males in question and discovered that they belonged to another closely related (sexually reproducing) species of fungus-farmer, Mycocepurus obsoletus, thus establishing that no males are known to exist for M. smithii.

He also dissected reproducing M. smithii queens from Brazil and found that their sperm storage organs were empty.

Taken together with the previous studies of the ants, Rabeling and his colleagues have concluded that the species is very likely to be totally asexual across its entire range, from Northern Mexico through Central America to Brazil, including some Caribbean islands.

As for the age of the species, the scientists estimate the ants could have first evolved within the last one to two million years, a very young species given that the fungus-farming ants evolved 50 million years ago.

Rabeling says he is using genetic markers to study the evolution and systematics of the fungus-gardening ants and this will help determine the date of the appearance and genetic mechanism of asexual reproduction more precisely in the near future.