Abstract Borellia bruneri, a common grasshopper in much of the grasslands of Argentina and Uruguay, is considered, according to the categories widely accepted for defining the pest status of grasshopper species, a “Frequent plague of importance”. In order to determine fundamental aspects of its biology and reproduction, three cohorts of B. bruneri were monitored under controlled conditions (30º C, 14L: 10D, 40% RH). The total duration of nymphal development was 50.6 days, both males and females having five nymphal instars. There was a significant difference in the duration of the different stages within each cohort. In the three cohorts, the first instar duration (12.87 days) was longer than the rest, approximately 5.6 days more than the second that was the shortest (7.26 days). The average longevity of female adults was 56.6 days, and in males, 54.4 days. The number of egg-pods per female was 3.5 and the amount of eggs per egg-pod was 10.8. Mean fecundity was 37.9 eggs per female with an oviposition rate of 1.20 eggs/female/day. Finally, knowing the life cycle of B. bruneri is relevant in order to optimize the control measures for this species.

The grasshopper Dichroplus maculipennis is considered one of the most characteristic and damaging species of Argentina, mainly in areas of Pampas and Patagonia regions. In outbreak years, this species causes serious damage to grasslands as well as to implanted pastures and various crops. Considering this, the main goal of this study was to estimate the loss of forage caused by different densities of D. maculipennis in adulthood on a pasture of forage value as Festuca arundinacea, under field conditions. The experience was conducted in a field of Tandil County, during January 2016. Adult individuals of D. maculipennis were placed in cages in a sex ratio 1:1. Forage loss caused by three different densities was estimated with 8 ind/m², 16 ind/ m² and 32 ind/m². Three replicates were performed for each assayed density; also three cages were established without grasshoppers as control. The harvested biomass at the end of the experiment in control cages was 337,8 ± 7,5 g/m², in cages with a density of 8 ind/m² was 262,9 ± 11,8 g/m², those with 16 ind / m² was 227,6 ± 6 g / m² and in cages with 32 ind/m² was 154,6 ± 9,9 g/m². The three densities caused a significant decrease in the biomass of F. arundinacea respect to the control (p <0,0001). Plant biomass harvested from cages with the highest density of grasshoppers was significantly lower than that obtained from cages with the other two densities (p <0,05). One insect per day caused a forage loss of 0,02 ± 0,236 g/m², on average. From the results, it can be inferred that a density of 8 ind/m² would produce a forage loss of 749 kg/ha, 16 ind/m² would produce a forage loss of 1107,4 kg/ha, and with 32 ind/m² the loss would be 1873 kg/ha. The latter would cause a decrease of 55% of the biomass of pasture in one month.

Dichroplus maculipennis es una de las especies de tucura más característica y perjudicial de Argentina, principalmente en zonas de la región pampeana y la Patagonia. En años de explosiones poblacionales esta especie ocasiona importantes daños en pastizales naturales, pasturas implantadas y en diversos cultivos. Considerando esto, el objetivo principal de este estudio fue estimar la pérdida de forraje ocasionada por diferentes densidades de D. maculipennis en el estado adulto, sobre una pastura de valor forrajero como Festuca arundinacea, en condiciones de campo. La experiencia se realizó en un campo del partido de Tandil, durante el mes de enero de 2016. Se utilizaron jaulas donde se colocaron individuos adultos de D. maculipennis en una proporción 1:1 de machos y hembras. Se estimó la pérdida de forraje ocasionada por tres densidades diferentes: 8 ind/m², 16 ind/m² y 32 ind/m². Se realizaron tres réplicas por densidad ensayada y también se establecieron tres jaulas sin tucuras como control. La biomasa cosechada al final de la experiencia en las jaulas control fue 337,8 ± 7,5 g/m², en las jaulas con una densidad de 8 ind/m² fue de 262,9 ± 11,8 g/m², en aquellas con 16 ind/m2 fue de 227,6 ± 6 g/m² y en las jaulas con 32 ind/m² fue de 154,6 ± 9,9 g/m². Las tres densidades utilizadas ocasionaron una disminución significativa en la biomasa de F. arundinacea respecto del control (p<0,0001). Asimismo, la biomasa vegetal cosechada en las jaulas con la mayor densidad de tucuras fue significativamente menor a la obtenida en las jaulas con las otras dos densidades (p <0,05). En promedio un individuo por día ocasionó una pérdida de forraje de 0,236 ± 0,02 g. A partir de los resultados obtenidos, se puede inferir que 8 ind/m² producirían una pérdida de forraje de 749 kg/ha. Con 16 ind/m² la pérdida sería de 1107,4 kg/ha y con 32 ind/m² la pérdida sería de 1873 kg/ha. Esta última densidad ocasionaría una disminución del 55% de la biomasa de la pastura en el lapso de un mes.

Dichroplus maculipennis (Blanchard) and D. elongatus Giglio-Tos are two of the most important melanoplines in Argentina, both ecologically and economically. The postembryonic development and forage loss (consumption of Bromus brevis Ness + fallen material) caused by older nymphs (instars IV, V, VI) and adults of both species were studied under controlled conditions (30ºC, 14L:10D, 40% RH). Five nymphal instars were recorded in D. elongatus, and six in D. maculipennis. Total nymphal development was similar in both species (D. elongatus: 32 ± 0.70 days; D. maculipennis: 34.5 ± 0.37 days). Daily consumption increased from nymphal instars to pre-reproductive adult stage. In both species, pre-reproductive females had higher consumption rates than other stages considered (D. elongatus: 30.6 ± 0.56 mg dry weight/day; D. maculipennis: 48.7 ± 0.74 mg dry weight/day). In the reproductive stage, consumption decreased significantly in both sexes. When feeding, D. maculipennis let some plant material to drop, increasing total loss. The percentage of fallen material was greater in reproductive adults, representing 3.9% and 2.9% of the total daily loss for males and females, respectively. Females and males of D. maculipennis were heavier than those of D. elongatus (P < 0.05), and daily consumption was significantly higher (P < 0.05). Regardless sex and reproductive status, adults of D. maculipennis consumed 29.1 ± 0.64 mg dry weight/day on average, while one of D. elongatus 20.0 ± 0.3 mg dry weight/ day.