Ant–aphid mutualism: the influence of <i>Tapinoma ibericum</i> (Hymenoptera: Formicidae) on <i>Aphis gossypii</i> (Hemiptera: Aphidae) control by commercial and spontaneous natural enemies

The cotton aphid (Aphis gossypii) is a major pest of greenhouse peppers in southern Spain. Biological control using the parasitoid wasp Aphidius colemani is limited because the ant Tapinoma ibericum, engaged in a mutualistic relationship with aphids, protects them from parasitoid attack and thereby reduces parasitism success. To assess the impact of ants on pest biological control, an ant-exclusion experiment was conducted over two consecutive years in four experimental greenhouses. Pepper plants were infested with aphids and then treated with Aphidius colemani. The presence of natural enemies and fruit production were also evaluated. Excluding ants significantly increased the abundance of mummies by 22.2% and reduced the number of aphid colonies, while total aphid abundance showed variable, year-dependent effects and was not affected by ants. Ant presence negatively affected some natural enemies such as Chrysoperla carnea s.l., the mirid Nesidiocoris tenuis, and the ladybird Scymnus sp., had no effect on hoverflies and spiders, and increased the abundance of Aphidoletes aphidimyza, indicating contrasting responses among natural enemies. Fruit weight was not affected by ant presence. Overall, these findings confirm that T. ibericum reduces parasitism by A. colemani, and demonstrate that it modifies aphid spatial distribution, and reshapes the natural enemy community, but does not necessarily diminish crop production. These results suggest that combining A. aphidimyza with A. colemani could improve control of A. gossypii in ant-infested crops.