Mutualistic interactions between ants and hemipterans are mediated by the honeydew produced by the hemipterans. Previous works have demonstrated that the invasive mealybug Phenacoccus solenopsis produces abundant honeydew and attracts a large number of workers of the fire ant Solenopsis invicta. Mealybugs exhibit higher fecundity when tended by fire ants. The honeydew produced by P. solenopsis plays an important role in interactions between these two species. However, relatively few studies have focused on whether there is a cost to P. solenopsis mealybugs of being tended by S. invicta through changes in their excretion behavior and the quantity of honeydew produced. Our results indicated that the honeydew of P. solenopsis contains xylose, fructose, sucrose, trehalose, melezitose, and raffinose. The sugar concentration in the mealybug honeydew changed in an ant‐tended treatment. When tended by fire ants, the mealybugs generated honeydew with a significantly decreased xylose concentration. In contrast, the droplets showed a considerable increase in the melezitose concentration. P. solenopsis excreted honeydew more frequently when tended by S. invicta, but the weights of the droplets excreted by the ant‐tended mealybugs were significantly lower. In addition, S. invicta exhibited a significant preference for different sugars. Melezitose was visited more intensively than the other sugars in two choice tests. These results may suggest that, to attract more tending ants, mealybugs adjust their carbohydrate metabolism.
Although many reports suggested the economic importance of the red imported fire ant, Solenopsis invicta Buren, few attempts to test the hypothesis that the red imported fire ant-aphid mutualism enhances the occurrence of red imported fire ant on crops, thereby interfering with their flowering and fruiting and affecting their output. To address this problem, we compare the effects of red imported fire ant on the flowering and fruiting of self-pollinating and cross-pollinating crops by field investigations and indoor experiments. In the field, our results revealed that regardless of the aphid interaction, red imported fire ant preferred flowering mungbean plants, and their activities decreased the yields of single plants, total pod number, kernel number, and kernel weight. The interaction of red imported fire ant and aphids generated unfavorable effects on rapeseed yields per plant, total pod number, grain number, grain weight, and thousand-kernel weight and stimulated an elevated proportion of malformed seeds. However, the differences were not significant if only red imported fire ant was present. In the laboratory, although red imported fire ant display no apparent preference toward the seedlings of mungbean or rapeseed, the ants clearly favor the flowering plants of mungbeans. Therefore, this study indicated that one of the main mechanisms whereby red imported fire ants affect the crop yield is by compromising the reproduction processes.
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