**1. Introduction**

#### **1.1. Leaf–cutting**

Leaf-cutting ants of the genera *Atta* sp. Fabricius (Hymenoptera: Formicidae) and *Acromyr‐ mex* sp. Mayr (Hymenoptera: Formicidae) are among the best known species of the family Formicidae in the New World, mainly due to their behaviour of cutting live plants to grow the symbiotic fungus *Leucoagaricus gongylophorus* (Möller) Singer (Agaricales: Agaricaceae) [1] (Figure 1). This interaction, which emerged more than 50 million years ago [2] has evolved to such a complex level that the ants and fungi cannot survive separately; they live in symbiosis. The fungus supplies the ants with nutrients obtained from metabolising plant materials that can be easily assimilated. In exchange, its environment is highly protected by the ants, which remove contaminants and secrete antibiotics from their metapleural glands [3, 4].

The symbiotic fungus, which exhibits high carbohydrate and protein content but low content, constitutes the main food source for leaf-cutting ant colonies [5] and is the single nutrient source for the queen, larvae, and temporary alate castes. Only 9% of the energy requirements of adult workers, which ingest plant sap when handling plant fragments, are obtained from the fungus [6]. Moreover, the symbiotic fungus produces large amounts of enzymes, which are ingested by the ants and are returned to the fungal garden through faecal liquid to facilitate the digestion of plant tissue [7, 8].

Leaf-cutting ants are considered the main agricultural and forest pest in countries such as Brazil, as they attack plants at any stage of their development, cutting their leaves, flowers, buds, and branches, which are then transported to the interior of their underground nest [9]. A colony of *Atta laevigata* (F. Smith) (Hymenoptera: Formicidae) can cut approximately 5 kg

*urophylla* S.T. Blake) (Myrtaceae) [17]. Certain plant-derived substances can promote aggres‐ sive behaviour of ants towards their sisters, as reported for *β*-eudesmol extracted from eucalyptus leaves. [18, 19, 20] This sesquiterpene is able to modify the chemical composition of the worker's cuticle, impairing nest recognition, which triggers warning and aggressive behaviours among ants [20]. Plant extracts can also be toxic to the symbiotic fungus (*L. gongylophorus*), which represents an interesting target for new products for ant control. Such effects can be observed for extracts of *R. communis*, *Helietta puberula* R.E.Fr. (Rutaceae), *Simarouba versicolor* St. Hill (Simaroubaceae), and *Canavalia ensiformis* (L.) DC. (Fabaceae) [15,

Plant–Derived Products for Leaf–Cutting Ants Control

http://dx.doi.org/10.5772/55035

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**2. Leaf–cutting ants of the genera** *Atta* **and** *Acromyrmex* **and their symbiotic**

Leaf-cutting ants comprise over 12,000 species and are considered social insects because they participate in parental care, reproductive castes, overlapping generations, and a division of labour [24]. These insects live in permanent colonies and are holometabolous. Taxonomically, they belong to the order Hymenoptera, family Formicidae, subfamily Myrmecinae, and tribe Attini [25]. Leaf-cutting ants belong to the genera *Atta* Fabricius and *Acromyrmex* Mayr as well as the basal genera *Apterostigma* Mayr, *Kalathomyrmex* Klingeberg and Brandão, *Mycetagroi‐ cus* Brandão and Mayhé-Nunes, *Mycetarotes* Emery, *Mycetaphylax* Fr. Smith, *Paramycetophy‐ lax* Kusnezov, *Sericomyrmex* Mayr, *Trachymyrmex* Forel, *Pseudoatta* Gallardo, and *Attaichnus* Lazã. [21] The Attini tribe is found only in the Neotropical region and is distributed between

The leaf-cutting ants of the genera *Atta* and *Acromyrmex* (known as *saúvas* and *quenquéns* in Brazil, respectively) build nests composed of hundreds of underground chambers that are connected to each other and to the surface through galleries. The exterior of the nest usually exhibits a loose soil mound originating from the chambers formed by the nest [27]. Holes can be found in the loose soil mound or outside of it. According to Mariconi (1970), a large anthill

Leaf-cutting ants cultivate the symbiotic fungus *L. gongylophorus,* which is used as a source of food and of auxiliary enzymes that function in the ants digestive process [29]. After the origination of the ant-fungus symbiosis, a subsequent evolutionary step involved the acquis‐ ition of staphylae-rich monophyletic cultivars by the highly derived Attini (Figure 2), partic‐ ularly the *Atta* and *Acromyrmex* species, which collect only fresh vegetation as the fungal substrate. The conversion of vegetation into substrate requires several different operations and specialisations. The plants are cut by workers who have a head width of 1.6 mm or greater (other tasks, such as defence, involve larger workers), while care of the fungus requires very small workers, and intermediary steps in the garden are performed by medium-sized workers. Among ant species, this great evolutionary change seems to have placed the derived Attini on the path of producing larger and larger colonies due to the increased differences between the

may contain an estimated population of six million ants [28].

21-22 ,23].

of approximately 200 m2

**fungus,** *Leucoagaricus gongylophorus*

southern South America and the southern United States [26].

**Figure 1.** *Atta sexdens* and its fungal garden: mycelial care. Source: Arnhold, 2012.

of plant material/day [10]. Thus, these ants cause direct losses, such as the death of seedlings and reduction of tree growth. Indirect losses also occur as a result of the decreased resistance of trees to other insects and pathogenic agents [11].

Leaf-cutting ant control has been performed almost exclusively through the application of conventional insecticides, including cyfluthrin (pyrethroid), imidacloprid (neonicotinoid), furathiocarb (carbamate), sulfluramid (fluoroaliphatic sulfonamide), and fipronil (phenyl pyrazole) [12]. Due to the problems these products may cause to the environment and humans, their use has been restricted by governments and forest product certification bodies, which have demanded and encouraged the development of alternative control strategies to these insecticides, such as the use of plant-derived products, entomopathogenic fungi, and phero‐ mones [13].

Plant-derived products can be used to control ant populations through several mechanisms. Some of these substances can act directly against the ant, leading to its death, such as citrus seed oils obtained from *Citrus sinensis* (L.) Osbeck, *Citrus limon* (L.) Burm. f. or *Citrus reticula‐ ta* Blanco (Rutaceae) [14] and extracts from the castorbean (*Ricinus communis* L.) (Euphorbia‐ ceae) [15], timbo (*(Ateleia glazioviana* Baill.) (Leguminosae) [16] and eucalyptus (*(Eucalyptus* *urophylla* S.T. Blake) (Myrtaceae) [17]. Certain plant-derived substances can promote aggres‐ sive behaviour of ants towards their sisters, as reported for *β*-eudesmol extracted from eucalyptus leaves. [18, 19, 20] This sesquiterpene is able to modify the chemical composition of the worker's cuticle, impairing nest recognition, which triggers warning and aggressive behaviours among ants [20]. Plant extracts can also be toxic to the symbiotic fungus (*L. gongylophorus*), which represents an interesting target for new products for ant control. Such effects can be observed for extracts of *R. communis*, *Helietta puberula* R.E.Fr. (Rutaceae), *Simarouba versicolor* St. Hill (Simaroubaceae), and *Canavalia ensiformis* (L.) DC. (Fabaceae) [15, 21-22 ,23].
