Forage Loss Caused By Dichroplus Maculipennis (Acrididae: Melanoplinae)

DE WYSIECKI MARÍA LAURA; MARIOTTINI YANINA; LANGE, CARLOS E.

Illheus

Congreso; 12th International Congress of Orthopterology; 2016

Orthopterists Society

Grasshoppers are among the major groups of herbivorous insects in most grassland ecosystems. In many situations, they are considered harmful insects because they compete with livestock for available forage. The melanopline Dichroplus maculipennis (Blanchard) occurs in Argentina, Uruguay, Chile and Brazil. It is a polyphagous and univoltine species that presents obligatory embryonic diapause. Dichroplus maculipennis is considered the main grasshopper pest in Argentina, especially in areas of the Pampas and Patagonia regions, causing damage in grasslands and a wide variety of important crops. A major outbreak was recorded in the south of Buenos Aires province from late 2008 to early 2011 in an area of approximately 2.5 million ha.The aim of this study was to evaluate the forage loss caused by different densities of D. maculipennis under field conditions. Estimation of forage losses (plant material consumed + destroyed) was carried out with last (sixth) instars and adults. These developmental stages were selected because in most grasshoppers they tend to produce most of the damage. The study was conducted in Tandil, Buenos Aires province, in a pasture of Festuca arundinacea, the forage grass most commonly used in cultivated pastures of Argentina. Twelve aluminum-framed cages with wire-screened walls (70 x 50 x 50 cm) were placed, three replicates for each density tested (8 ind/m2, 16 ind/m2, and 32 ind/m2) and three cages without grasshoppers (0 ind/m2) as a control. The insects were placed in a 1: 1 male to female ratio. The experiment was carried out for a month Weather conditions favored pasture growth. Both, average precipitation and temperature of January were higher than the historical average values for the area. The pasture in absence of grasshoppers (control cages) increased approximately five times its biomass within one month from 68.2 ± 5.5 gr/m2 to 337.8 ± 7.5 gr/m2. In presence of grasshoppers, a significant difference in the amount of biomass at the end of the experience was recorded. The reduction of plant biomass produced by D. maculipennis at the three tested densities was significantly different from control (p