Impact of the Invasive Argentine Ant in Citrus Agroecosystems: Effects on the Diversity and Frequency of Native Ant Species Foraging on Tree Canopy.

Manuela Branco,José Carlos Franco,Vera Zina

doi:10.3390/insects11110785

Abstract

Simple SummaryWe aimed at assessing the impact of the Argentine ant invasion on the native ant community in citrus ecosystems. We compared the Argentine ant’s invaded and uninvaded citrus orchards in the south of Portugal, estimating species richness and the frequency of ant assemblages foraging on the tree canopy. The results suggest that the Argentine ant has a negative impact on the native ant community structure, markedly reducing the diversity and frequency of native species. This impact was more or less pronounced depending on the season. Possible implications for citrus pest management are discussed.The invasion of the Argentine ant, Linepithema humile (Mayr) (Hymenoptera, Formicidae) can alter the entire ecosystem with serious impacts on the native community structure (e.g., ant diversity) and processes (e.g., trophic interactions) leading to biodiversity loss and pest outbreaks. Most studies addressing these impacts have been conducted in natural or semi-natural areas, few are those conducted in agricultural ecosystems, such as citrus orchards. These are dominant agricultural ecosystems in Mediterranean landscapes. Furthermore, most studies have been conducted in a short span, not evidencing seasonal fluctuations. In this work, we assessed the ecological impact of the Argentine ant on the native ant communities in citrus orchards, in the region of Algarve, southern Portugal. By using principal response curve, we compared seasonal variation on ant assemblages in invaded and uninvaded citrus orchards foraging on tree canopy from a two-year sampling. The Argentine ant had a marked negative impact on the native ant community foraging on citrus canopy. In the uninvaded orchards, the native ant community had a rich assemblage composed of 16 ant species, in its majority (72%) controlled by the dominant species Lasius grandis Forel, Tapinoma nigerrimum (Nylander) and/or Pheidole pallidula (Nylander). In the invaded orchards, the native ant community was poorer and highly modified, mostly dominated by the Argentine ant (80%). Apparently, the only native ant species not affected by the presence of the Argentine ant was Plagiolepis pygmaea (Latreille). A significant negative effect was found between the proportion of infested trees by L. humile and the number of native ant species per orchard. Differences in the native ant community in the invaded and uninvaded orchards persisted over seasons and years. However, negative impacts were higher in the spring and summer, and less pronounced in the autumn. We discuss implications for citrus pest management.

Highlights

Ant invasions represent a worldwide concern and have been the subject of the largest number of publications on invasive insect studies in recent years [1]
(41% of the specimens), Plagiolepis pygmaea (Latreille) (22%), T. nigerrimum (12%), P. pallidula (10%), and P. schmitzii Forel (7%) represented 92% of the collected specimens, whereas in the case of invaded orchards, 99% of the specimens belonged to L. humile (80%) and P. pygmaea (19%) (Figure 2)
We showed that the Argentine ant has a negative impact on the native ant community structure and that this effect is more or less pronounced depending on the season period

Summary

Introduction

Ant invasions represent a worldwide concern and have been the subject of the largest number of publications on invasive insect studies in recent years [1]. Most of the introduced ant species are usually not detected and usually do not constitute a threat to native fauna. Those species that become invasive are very successful and considered a serious threat to the world’s native biodiversity [2,3]. The causes underlying the ecological success of invasive ants have been documented [4]. It seems that a combination of characteristics such as omnivory, unicoloniality, absence of competitors and natural enemies makes them successful invaders [4]. It has been recognized that the Argentine ant can displace the native ant community leading to dramatic impacts on the ecosystems [4,6,7,8,9,10]

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Discussion

Conclusion