Abstract:22 Ants can act simultaneously as predators and as hemipteran mutualists, and thus may affect 23 the composition and the population dynamics of a wide arthropod community. We

Although ants act as plant biotic defences, in agricultural ecosystems they are often associated with outbreaks of honeydew-producing pests mainly due to the protection they offer to the plant feeders in exchange for honeydew. In such an interaction ants may alter the abundance, diversity and community structure of predators and parasitoids. In the present study, we conducted ant-exclusion experiments in three commercial citrus orchards, each one dominated by one ant species (Pheidole pallidula, Lasius grandis or Linepithema humile) during two consecutive years (2011 and 2012). We then compared the abundance, species richness, diversity and community structure of predators and parasitoids between the antallowed and ant-excluded treatments. A total of 176,000 arthropods belonging to 81 taxa were captured and identified. Regarding abundance, our results showed a species specific response between treatments. When examining functional groups, in the ant-allowed treatment, seven species of predators decreased and four increased in abundance, whereas four species of parasitoids decreased and 18 increased in abundance. The species richness (S) was significantly lower for predators and higher for parasitoids in the ant-allowed treatment. The Shannon diversity index (H) was not different between treatments in the case of predators, whereas in the case of parasitoids diversity was significantly higher in the antallowed treatment. Finally, the community structure of predators and parasitoids was not significantly different between treatments. These results suggest that ants in the citrus agroecosystem are not associated with a dramatic decrease in natural enemy abundance or biodiversity; on the contrary ants were associated with increased parasitoid species richness and diversity. Despite the fact that ants have no negative impact on the abundance and diversity of predators and parasitoids at the community level their impact on specific natural enemy species, mainly predators, may explain the highest pest densities associated with ants in citrus.

Generalist arthropod predators not only prey on herbivores but also may engage in competitive interactions by attacking and consuming conspecifics (cannibalism) or other predators (intraguild predation [IGP] and hyperpredation). These types of interactions are quite common among predators used in biological control. Although there is evidence that nonprey food relaxes cannibalism and IGP, there is little information regarding the impact of the quality of the nonprey food. Herein, we examined how pollen of different nutritional quality (pine, narrow-leaf cattail, or apple) impacted 1) the cannibalism by females of Euseius stipulatus (Athias-Henriot) (Acari: Phytoseiidae) on conspecific larvae, 2) the reciprocal predation between gravid females of E. stipulatus or Iphiseius degenerans (Berlese) (Acari: Phytoseiidae) and heterospecific larvae, and 3) the predation of E. stipulatus on the eggs of the aphid predator Aphidoletes aphidimyza (Rondani) (Diptera: Cecidomyiidae). E. stipulatus cannibalism was significantly reduced in the cattail pollen treatment, whereas in the pine pollen it did not significantly differ from control (no food). Predation between I. degenerans and E. stipulatus was significantly reduced in the cattail pollen treatment as compared to the control treatment. Finally, predation of E. stipulatus on A. aphidimyza eggs was significantly reduced when cattail or apple pollen was provided compared to the pine pollen or control treatments. These results suggest that cattail or apple pollen is suitable for mitigating negative interactions among generalist predatory mites used in biological control.

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