Leaf-cutting ants in the genus Atta F. (Formicidae, Attini) are among the most important pest arthropods in Central and South America, consuming more vegetation than any other animal group. Among the organisms attacking ants in nature, flies of the family Phoridae have been proposed as the most promising biocontrol agents for pest ants. Four phorid species, Apocephalus setitarsus Brown, Myrmosicarius brandaoi Disney, Myrmosicarius gonzalezae Disney, and Eibesfeldtphora trilobata Disney, were reared from ants collected at Atta vollenweideri Forel nests and off foraging trails in Santa Fe province in Argentina. E. trilobata attacked larger ants and had bigger adults than the other species, also exhibiting the longest developmental time. Correlations between size of hosts and size of adults, as well as between size of adults and developmental times, could be established only in some cases. No differences were found between the sizes of the hosts from which males and females emerged. The natural percentage of parasitism varied throughout the seasons and seemed to be influenced by the extreme drought affecting the study site. We discuss why all four species would be suitable candidates for integrating an assemblage of biocontrol agents against A. vollenweideri.

Tetranychus urticae is a serious pest of several crops worldwide. It performs differentially on diverse hostplant species. Because dispersion is mainly passive, the process of host-plant selection should be viewed in terms of host-plant acceptance and not in terms of host finding. The objectives of this study were to investigate: (1) the acceptance of strawberry (S) in comparison with onion (O), leek (L) and parsley (P) by T. urticae; and (2) the suitability of these host plants for the performance of T. urticae, in terms of fecundity and survival. Host-plant acceptance was measured through females that settled on a test plant or females that left for another host plant. In another experiment, for a duration of 5 days, individual newly mated females were assigned to discs of each host plant and the fecundity, the maximum number of offspring obtained from one female that settled on the disc, the survival and the percentage of females that oviposited at least one egg were analysed. A choice test to measure the preference of females for different host plants was performed. Movements took place towards (S) from the three plants: (O), (L) and (P). Mites significantly moved to other places in the Petri dishes from leek-origin discs. Dispersal of T. urticae from (S) to other host-plant discs was similar for all plants. Mean fecundity was higher on (S) than on the other plants. The maximum number of offspring per female was highest on (S), lowest on (L) and (O), and intermediate on (P). Survival of females and percentage of females that laid at least one egg were independent of the host plant. The choice test showed that oviposition was higher on (S) and (P) and very poor on (L) and (O) and that more females settled on (S) and (P). Although mites migrated from parsley to strawberry, the first host plant has a higher acceptance of T. urticae in terms of maximum number of offspring per female than onion and leek, and a lower performance in terms of fecundity than strawberry. Parsley could be a good candidate for an associate plant in a strawberry crop; however, it needs more research under field conditions.

Leafcutter ants in the genus Atta (Hymenoptera: Formicidae: Attini) are considered major pests of agriculture and forestry in the Neotropics. Phorid flies (Diptera: Phoridae) have been proposed as viable candidates for biological control of ants because of the importance of their trait-mediated effects on their hosts. However, the impact of different densities of phorid flies has never been assessed in the field. Experiments were conducted by isolating 3-m sections of Atta vollenweideri Forel foraging trails with tunnels, and sampling ants in trails with 0, 1, or 4 Eibesfeldtphora trilobata Disney female parasitoid flies. Samples were collected every 30 min from these trails. We also collected a sample before introducing the parasitoids and another one 30 min after removing them from the trail. We measured traffic of ants on the trails, weight and type of plant material transported, and the proportion and size of the workers collected. The presence of phorids on the trails reduced the ant traffic and amount of plant material transported into the nests and decreased the proportion of workers on the trails in the size range preferred as hosts by the flies. The effect on worker size, as well as the lag effect recorded after phorids were removed from the tunnels, was more pronounced with four phorids. The presence of phorids also affected the weight of monocotyledon and dicotyledon material transported. Even at the minimum density possible, phorids significantly influenced a key aspect of the colony life, the food intake through foraging. From an applied point of view, our results show that releases of these phorids into the field should not necessarily involve many individuals to reduce foraging by A. vollenweideri, making them potentially useful candidates for biological control of these ants.

Phorid flies have been considered viable options for biological control of leaf-cutter ants because they are highly specific to these hosts, producing direct mortality and also affecting the normal functioning of colonies. Designing protocols for mass rearing of these insects requires knowing the temperature and humidity conditions that optimize their development in terms of duration, survivorship and longevity of adults. We reared Apocephalus setitarsus Brown, Eibesfeldtphora trilobata Disney, and Myrmosicarius brandaoi Disney, which are specific leaf-cutter ant parasitoids of Atta vollenweideri Forel, and Apocephalus neivai Borgmeier and Myrmosicarius catharinensis Borgmeier, which are parasitoids of Acromyrmex lundii Guérin-Méneville. Phorids were maintained under one of five different rearing conditions, 20°C high humidity (20HH), 24°C low and high humidity (24LH and 24HH), and 28°C low and high humidity (28LH and 28HH). Flies from all species could complete their development under all the conditions tested. As expected, the 20HH treatment significantly lengthened all developmental periods in all species, whereas the shortest duration was achieved under 28HH. Although pupal survivorship was highest at 24HH, the greatest longevity of adults was achieved at 20HH. Percentage of pupae obtained and pupal survivorship also exhibited the highest values at 24HH. The rearing efficiency index was highest for all species at 24HH. Therefore, we suggest this temperature and humidity combination as the most suitable for rearing these species, whereas the 20HH treatment is ideal for maintaining adults for longer periods, which would be advantageous for synchronizing matings and mass releases of adults in the field.

In southern South America, Ada vollenweideri Forel (Hymenoptera: Formicidae) is a significant pest of several crops and forestry, also considered to reduce the carrying capacity of pastures. The most usual control method used in Latin America is the application of synthetic pesticides, mainly chlorpyrifos and fipronil. However, no studies have assessed the effects of these agrochemicals on natural enemies of ants. We aimed to evaluate the efficiency of these pesticides on leaf-cutter ants' control and to test their effect on phorid fly parasitoids. Chlorpyrifos failed to exert complete control over ant colonies in the field and was gravely detrimental to specific parasitoids, reducing their percentage of parasitism, pupal survivorship, and adult longevity. Fipronil, however, exerted complete control over the treated colonies. Laboratory tests using both pesticides, either on ants from foraging trails or on pupariae, showed that chlorpyrifos and fipronil decreased larval and pupal survivorship, as well as adult longevity of parasitoids, in comparison to controls. In conclusion, these pesticides will likely affect parasitoids with regard to their reproductive capacity, leading to the decreased levels of natural parasitism observed in the field after treatments. We discuss why neither pesticide should be taken into account for integrated pest management programs.

The damage to plantations by pests is often determined by perceptions rather than objective data, resulting in excessive use of pesticides. Leafcutter ants are considered important pests to plantations in America. We evaluated the difference in Pinus taeda biomass consumption by four Acromyrmex leafcutter ant species which co-inhabit plantations of this pine species. These ants exhibit morphological and behavioral differences, i.e., Ac. heyeri has mandibles adapted to cut monocots, while the other species cut dicots, which may result in differences in their consumption of pine. We collected the plant biomass that ants carried into their nests and recorded the foraging activity in different seasons throughout a year. The P. taeda biomass carried into leafcutter nests was less than 20 % compared to total plant biomass. Colonies with greater foraging activity carried a greater amount of total biomass, but they did not carry more pine biomass. The leafcutter ant species studied differed in their use of pine biomass, but not of total biomass. Acromyrmex ambiguus and Ac. crassispinus were the species carrying the greatest amount of pine biomass and with more colonies using pine, whereas very little amounts of pine were carried by Ac. heyeri and by very few colonies. Thus, leafcutter ant species do not cause the same damage to pine plantations. Our results also highlight the importance of pest management strategies based on a thorough knowledge of the biology of the species, including those characteristics which can predict the use that each species will make of the plantation.

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https://doi.org/10.25085/rsea.763409Nuevos registros y nuevas interacciones hospedador-parasitoide de fóridos (Diptera: Phoridae) que parasitan hormigas cortadoras de hojas (Hymenoptera: Formicidae) en Argentina RESUMEN. Las hormigas cortadoras de hojas son una de las plagas más importantes de la región Neotropical. En el presente estudio, fueron recolectados representantes de cuatro provincias de Argentina, con el objetivo de identificar las especies de fóridos que las parasitan. Como resultado, se registraron siete especies de fóridos, Apocephalus neivai Borgmeier, Ap. noetingerorum Disney, Neodohrniphora unichaeta Disney, Myrmosicarius catharinensis Borgmeier, M. cristobalensis Disney, M. crudelis Borgmeier y M. gracilipes Borgmeier, obtenidos en hormigas cortadoras de hojas de las especies Acromyrmex ambiguus Emery, Ac. crassispinus Forel, Ac. heyeri Forel, Ac. lobicornis Emery y Ac. lundii Guérin. Asimismo, son reportados todos los registros previos de hospedadores y su distribución geográfica en Argentina para las siete especies de fóridos. Se citan nuevos registros en todas las especies estudiadas, ampliando así sus rangos geográficos y estableciendo once nuevas interacciones hospedador-parasitoide. Nuestros datos amplían el conocimiento de este poco estudiado sistema y proveen importantes consideraciones para el uso potencial de estos parasitoides como controladores biológicos de hormigas cortadoras de hojas. PALABRAS CLAVE. Enemigos naturales. Rango geográfico. Sistema hormiga-parasitoide.ABSTRACT. Leafcutter ants are one of the most important crop pests in the Neotropics. In the present study, several specimens were collected from four provinces in Argentina in order to determine the species of phorid flies parasitizing them. We report our findings on seven phorid species, Apocephalus neivai Borgmeier, Ap. noetingerorum Disney, Neodohrniphora unichaeta Disney, Myrmosicarius catharinensis Borgmeier, M. cristobalensis Disney, M. crudelis Borgmeier and M. gracilipes Borgmeier, over the leafcutter ants Acromyrmex ambiguus Emery, Ac. crassispinus Forel, Ac. heyeri Forel, Ac. lobicornis Emery and Ac. lundii Guérin. All the known hosts and geographic ranges for these seven phorids in Argentina are provided. The seven phorid species represent new records for all the provinces studied, expanding their geographical ranges; furthermore, we establish a total of eleven new host-parasitoid interactions. Our data expand the knowledge of this little studied system and provide important considerations for the potential use of these parasitoids as biological control candidates of the leafcutter ants.