Preference and performance in grasshopper, Melanoplus sanguinipes (Orthoptera: Acrididae), feeding on kochia, oats, and wheat: implications for population dynamics

Distribution in binary choice experiments using growing plants or cut leaves indicated that the grasshopper Melanoplus sanguinipes (F.) preferred wheat (Triticum aestivum (L.)) and kochia rather than oats (Avena sativa (L.)). Wheat was preferred more than kochia but only in experiments with cut leaves. The amount of each plant consumed was correlated with preference. Percentage of survival of grasshoppers to adult was highest when they were fed wheat (48.4), followed by oats (16.4) and kochia (10.4). Rate of development was the same in both sexes and was in the same order as survival, ranging from 33 d on wheat to 50 d on kochia. Mean adult weight was affected by diet more in females than in males, and was greater in wheat, followed by oats and kochia. Degree of development of the ovaries in surviving adults was affected also by diet and was in the order wheat oats kochia, and showed the greatest variance of any parameter measured. The average number of eggs per female was 18.4 when grasshoppers were reared on wheat, 7.9 on oats, and 4.7 on kochia. Grasshoppers fed kochia had the highest percentage of egg viability (70.7), followed by those fed on oats (66.1) and wheat (53.1). Biotic potential of M. sanguinipes (a summation of the effects of survival, development, and reproduction) was highest on wheat and lowest on kochia. Thus, grasshopper preference was not correlated with performance on oats and kochia. Where kochia is the dominant plant species, it is likely to have an adverse effect on susceptible species