Mites Protect Valencian Oranges From Bugs

One of the most popular varieties of citrus grown in the U.S. is the Valencia orange tree with the botanical name Citrus Sinensis.  These citrus trees are susceptible to thrips-a fruit pest.

A new study has found that soil-dwelling predatory mites are perfect  to address the plague of thrips in citrus caused by Pezothrips kellyanus, a tiny insect that affects the skin of the fruit.

This study was conducted by researchers from the University of Politecnica de Valencia in collaboration with the University of Navarra and the Belgian company, Biobest Belgium NV.

Valencia professor Ferran García explains that thrips are a serious economic problem for the citrus sector: "This bug causes a round scar on the top of fruit. This is a purely aesthetic condition, but with serious consequences. For example, half of the Valencian production is exported and a fruit affected by this pest cannot be exported, with the economic losses it entails."

The researchers went about studying the fauna in orchard soil and its effect on the pest, to reach a solution.

"This is the first study in Spain that has evaluated the behaviour of soil mites and how their presence can affect the thrips population and, therefore, the presence or absence of damage to the crop," says researcher Cristina Navarro.

The researchers analyzed four citrus orchards that were located in Valencia and identified nearly 15 species of mites. Out of which the most abundant ones were the Parasitus americanus (Parasitidae) and Gaeolaelaps aculeifer (Hypoaspis aculeifer).

From the results they found that the mite that best could act against the plague was Gaeolaelaps aculeifer.

"The study concluded that there is a direct relationship between a high presence of this mite in the earth and a low presence of thrips on the fruit. This suggests that these mites could be an alternative to the chemical products currently used," says Ferran Garcia.

Several tests were conducted in order to determine if foliar applications of insecticides or the addition of organic matter to the soil affects the abundance of soil-dwelling predatory mites.

"Those lands to which manure composting is added have more predatory mites, while a treatment with the insecticide chlorpyrifos does not affect their number," adds Cristina Navarro.

The work has been published recently in the journal Biological Control.