Biological control discussed at big scientific conference at SLU

– Molecular tools facilitate the detection of parasitoids and prey as they only need small quantities of DNA to work and can provide identification to species, regardless of the life stage of the individual, said Tara Gariepy.

In addition, it is possible to detect DNA from several species of predators and prey at the same time. This provides a better picture of all the interactions and key players and can make a biological control program more successful.

As examples, Tara Gariepy talked about lygus plant bugs that is a serious pest in Canada of a variety of fruit and vegetables. In this case, it was necessary to introduce a foreign parasitoid as native enemies were not effective. Tests showed that the tested parasitoid would have minimal impact on non-target plant bugs in Canada. Another example is the brown marmorated stink bug in Canada. This bug has recently invaded and the idea to use egg parasitoids against this pest has been put forward.  The potential risks and benefits with releasing exotic parasitoids to control these stink bugs is now being investigated.

– Lab experiments can complement the molecular studies. Results from the molecular data can be interpreted with behaviors that we have seen in the lab, concluded Tara Gariepy.  

Tracking an invasive fly in the field

The invasive spotted wing drosophila from south east Asia has spread all over Europe and the Americas. Females lay eggs into undamaged ripening fruits and the fly causes large economic losses in fruit and berry production. Can natural enemies be used to control this pest?

Sarah Wolf from Agroscope, Research Division Agroecology and Environment in Zurich, Switzerland talked about a method to track predation on Drosophila suzukii in the field. A simple and cost-effective assay to detect DNA in the gut of predators has been developed. Using the new assay, the spotted wing drosophila were found to be consumed by earwigs, spiders and predatory bugs. Therefore, these groups could serve as potential biological control agents.

Do food webs change after fertilization?

Oskar Rubbmark from the University of Innsbruck in Austria has investigated if predator food webs change in response to fertilization. Food webs in fields fertilized with manure, compost and inorganic fertilizer and unfertilized plots were studied during 2 years. In total Oskar Rubbmark caught 14 000 generalist predators. Using molecular methods he looked at the diet of 6500 individuals of the most common predators, and explored if they had been feeding on for example aphids, cereal leaf beetles, springtails and earthworms. Fertilization was found to affect the whole food web, from prey to predators. The conclusion was that the effects of the biocontrol depend on both fertilizer type and predator traits.

Biological control of aphids in Chile

In Chile, a biological control program was started in the 70ies after the English grain aphid were accidentally introduced. Nine foreign natural enemies to the aphid were introduced. How well is the biological control working now? Blas Lavandero from Universidad de Talca in Chile talked about a study where he assessed population dynamics of two different groups of natural enemies; parasitoids and lady beetles. Natural enemies were collected and their gut content was analysed with molecular analyses. It has often been shown that complex landscapes harbor a richer community of natural enemies which may result in improved biological control. However, surprisingly, in this study, somewhat higher parasitism rates were observed in simple landscape contexts, than in simple ones, a pattern that could at least partly have been driven by intraguild predation by lady beetles. Blas Lavandero detected differences in which groups ate aphids depending on season, and on environmental and management regimes. Overall, he concluded that the biological control of the English grain aphid still works well in Chile.

Biological control needed in urban agriculture

Many cities in USA suffers from significant population decline, something that creates vacant green spaces in the cities. These plots are now in many cases used for urban agriculture. Insects pests, like the cucumber beetle, can be a big problem. The farmers rarely use pesticides as people are close by and other alternatives, like biological control, are needed.

Mary Gardiner from The Ohio State University in USA has investigated what advice researchers should give to urban growers when fighting the striped cucumber beetle.

– What advices can we give to urban farmers? The advice is mostly the same now as it has been for decades: conserve a high diversity of predators. But does a higher natural enemy richness really help? Asked Mary Gardiner.

Mary Gardiner and colleagues investigated natural enemies to the cucumber beetle in organic and conventional squash fields.  Across all sites, they found a neutral relationship between pest abundance and total predator abundance and richness measured in pitfall traps. However, when they compared cucumber beetle density and the richness of hand-collected predators testing positive for cucumber beetle DNA they found a negative relationship, suggesting that a higher predator diversity may indeed lead to enhanced pest suppression.

– It has been a very interesting conference, where researchers from different field has gotten the chance to talk and learn from each other, says Mattias Jonsson.