Murcia develops effective biocontrol method for mite pest that infests citrus crops

The authority of the Spanish region of Murcia is seeking to put an end to a plague of small insects that impacts its extensive citrus crops. These are tetranid mites, against which the region's Department of Agriculture has been testing biocontrol mechanisms based on the small beetle Stethorus punctillum. 

The research, carried out in the south of Murcia, indicates that, after using this biocontrol, the total damage by these species on harvested fruit was less than 5% in the worst case.

Tetranychid mites represent one of the main threats to Mediterranean fruit and vegetable production. Their threat is such as in the case of the red spider mite (Tetranychus urticae) that can limit the economic viability of citrus crops.

Therefore, the first research carried out between 2018 and 2019 sought to test biocontrol solutions on this small mite. Given its good results, the Regional Agricultural Office has sought to extend the mechanism to other types of tetranychid mites, developing a new production model for S. punctillum using host plants Carica papaya (papaya), Solanum melongena (eggplant) and Solanum nigrum (black nightshade), under controlled conditions for multiplication. 

To this end, an insectary was built in Mazarrón to be able to test throughout the season on a 200-hectare citrus farm. "The design had to be able to maintain favorable conditions for the development of tetranychids as phytophagous arthropod prey and the predatory acarophagous arthropod to multiply and, at the same time, favor the vegetative stability of the host plants," explains David López Romero, from the Fuente Álamo - Mazarrón Regional Agricultural Office, in an article published in the Spanish journal Phytoma.

After releasing the predator in the field, the results of the research revealed that the combination of S. punctillum, together with the suppression of phytosanitary treatments, plus the measures adopted to favor its establishment, have been a decisive factor in the stability of the mite in the field and in the significant reduction of fruit damage by T. urticae compared to previous seasons. 

The installation of banks with S. nigrum as host plant helped the coccinellid to distribute and implant in a better way. As for damage by Panonychus citri (citrus red mite) and  Eutetranychus orientalis (oriental citrus mite), this occurred only on leaves and young plantations, and had no effect on crops. López Romero pointed out that in the case of E. orientalis, "the inoculative releases, together with the agronomic measures adopted, were insufficient to stop its exponential development". Leaf damage caused by this pest reached a maximum value of 81% in the most unfavorable variable, with no impact on fruit quality.

The technician emphasizes that in this work "S. punctillum has acted as an umbrella species, favoring considerably the increase of the biotic potential of the remaining auxiliaries against existing and new threats". Thanks to this, the biological control of other pests, such as diaspididae and pseudococcidae, was more effective than in previous campaigns, as in the case of the successful control of a localized outbreak of the cotonet Delottococcus aberiae through the mass release of Cryptolaemus montrouzieri as the only measure.

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