Relating feeding rates to sex and size in six species of grasshoppers (Orthoptera: Acrididae).

Abstract

Nymphs and adults of both sexes of six species of grasshoppers. Camnula pellucida, Dissosleira carolina, Melanoplus infantilis. M. sanguinipes, M. packardii and M. bivillalus, were fed wheat seedlings to determine daily feeding rates. The relationships between the feeding rates and five indices of body size were checked with five types of equations - power, parabolic, exponential. linear, and logarithmic. For combined data for all species. the power equation (y = axb) produced the best correlations with the feeding rate being proportional to the 1.56 power of pronotum length, 1.87 of femur length, 1.94 of body length, 0.72 of live weight, and 0.66 of dry weight. The power equation underestimated nymphal feeding and overestimated adult feeding. Better correlations were obtained when separate power equations were used for nymphs and adults. While the b parameters for the nymph equations did not differ significantly from those for the adult equations, the a parameters for nymphs were much larger, reflecting that nymphs ate more relative to their size than adults. For individual species, the parabolic equation (y = a + bx + cx2)was as good or sometimesbetter than the power equation. Generally, ranking the indices of body size by their coefficients of determination (r values) produced the following hierarchy: pronotum length (best), femur length, live weight, dry weight, and body length (worst). However, as the differences between the best and worst indices were minor (usually less than 10%) and as live weight and body length are easy to determine, we recommend the use of either of these two indices for estimating feeding rates.