Pest insects in natural and sown pastures of Paraguay

Paraguayan livestock production is based mainly on the use of natural and sown pastures as basic cattle feed. Several genera of harmful insects reported in forage grasses can cause damage to both yield and quality of forage. A review of the insect collection of the Plant Protection Area of the Faculty of Agrarian Sciences, National University of Asunción was carried out, in order to prepare a list of insects with incidence in grasses. Then random sampling of different species of Poaceae showing insect damage in open areas of paddocks grazed by cattle was carried out during 2014‒2017 in all Regions of Paraguay. Thirteen different genera and species of pastures were collected and 20 species of insects were identified in the following orders: Hymenoptera (Formicidae family: 5 species); Isoptera (Termitidae: 3 species); Hemiptera (Cercopidae: 6 species; Lygaeidae: 1 species); Lepidoptera (Noctuidae: 2 species); and Orthoptera (Acrididae: 3 species). The most common forms of damage observed in pastures were: leaf consumption (25%), leaf cutting (25%) and leaf yellowing-drying (35%).


Introduction
Paraguayan cattle ranching has experienced a significant improvement in number and quality in the last 20 years, and Paraguay is the seventh largest beef exporter in the world (ARP 2017). The country currently has 15 million hectares being used for livestock, and sown (5.6 million ha) and natural pastures (10 million ha) are the primary feed source for cattle, since it is the most economic and practical approach to meat production (Glatzle and Stosiek 2001;ARP 2017). This has created an ideal environment for the proliferation of different genera of insects, which can be harmful to forage crops (Fowler 1979;Glatzle 1999;Benítez 2002;Sarubbi 2016 of these insects are widely distributed over the American continent and cause a range of symptoms from defoliation to death of plants (Gallo et al. 2002;Brandão et al. 2011). Knowing the distribution and potential hosts of insects and damage caused is an important step in the development of adequate management strategies (Picanço et al. 1999;Nakano 2011).
The objective of this work was to identify harmful insects and determine their distribution throughout Paraguay, plant hosts infested and description of damage caused.

Materials and Methods
First, a review of the insect collection of the Plant Protection Area of the Faculty of Agricultural Sciences, National University of Asunción was carried out, in order to produce a list of registered pests causing damage to pastures. Subsequently, insect collections were carried out at random, Insect pests were collected, recording date, location, host and type and extent of damage, were photographed and immediately deposited in plastic containers for identification. The collection was manual using an entomological sweep net (50 cm ring diameter and 1 m bag length). The samples were transported to the Entomology Laboratory and examined with a stereoscope for identification. Insects were identified using the following reference sources: Fowler (1979), Kidono (1982), Glatzle (1999), Valério et al. (1999), Gallo et al. (2002), Sarubbi (2016) and Tolotti et al. (2018).

Results and Discussion
Twenty (20) species of insects in the orders Hymenoptera, Isoptera, Hemiptera, Lepidoptera and Orthoptera were found on 12 pasture hosts (Table 1). In Hymenoptera, 6 were in Formicidae family; in Isoptera, 3 were in Termitidae; in Hemiptera, 1 was in Lygaeidae and 6 in Cercopidae; in Lepidoptera, 2 were in Noctuidae; and in Orthoptera, 3 were in Acrididae.
The Urochloa and Megathyrsus genera represent the most important pasture grasses in the country, and consequently the greatest variety of insects was found on them. A unique case was observed in Urochloa arrecta × U. mutica (tangola grass), which was the exclusive host of Blissus antillus (grass bug). In relation to the occurrence of insects across Regions, some species, such as defoliating ants and cicadas, cover the whole country, while other species are confined to certain regions or places, such as the locust (Staurorhectus longicornis) and the cutter ant (Atta vollenweideri) in Chaco. The types of damage to pastures most commonly observed were: leaf consumption 25% [caterpillars (Mocis latipes, Spodoptera frugiperda) and locusts], cutting 25% (cutter ants) and leaf yellowing and drying 35% [grass bug and spittlebug (Notozulia entreriana and Mahanarva fimbriolata)] (Table 1).
Insects with the highest number of species (12) and distribution were cutter ants and spittlebug as mentioned by Fowler (1979), Kidono (1982), Glatzle (1999), Benítez (2002) and Sarubbi (2016). Valério (2006) and Tolloti et al. (2018) consider that spittlebugs are among the most important harmful insects of tropical pastures, attacking several genera, species and varieties, as observed in this research, as they were present in the whole territory of Paraguay and with a wide host range.
Incidence of Blissus antillus in tangola pasture agrees with reports of Valério et al. (1999) and Fazolin et al. (2012), who found that tangola grass (a natural Urochloa hybrid) and Urochloa arrecta were the only hosts of Blissus antillus in Brazil.
The damage caused by termites is considered indirect since this species develops mounds that are obstacles for agricultural machinery, causing loss of useful area in the paddocks.
Occurrence of most of these insects is seasonal and some appear in large numbers at specific times. Some which can cause serious damage are: caterpillars (Mocis latipes), bug (Blissus antillus) and cicadas (Notozulia entreriana and Mahanarva fimbriolata), as was mentioned by Gallo et al. (2002) and Tolotti et al. (2018).

Conclusions
This study has provided an overview of the range of insects which occur in pastures in Paraguay. Whether or not active measures to control them should be undertaken would depend on the extent of damage they cause and the impact on both pasture production and resultant animal performance. Observations on degree of damage to pastures under a range of conditions should supply some information on which to base decisions.