Insect response to mixture and monoculture patches of Michigan old-field annual herbs

1. The response of insects to the presence of discrete arrays of mixture and monoculture plots of weed species normally dominant in first-year Michigan old-fields was studied. 2. Plant species used were Amaranthus retroflexus, Chenopodium album, Panicum capillare and Setaria viridis. 3. Two experiments were implemented, one with pure stands of each species and the other with mixture stands of equiproportionate numbers of each plant species (Fig. 1). 4. Sucking insects had significantly higher weights, lower diversities and greater expressions of dominance in Chenopodium stands (Tables 2 and 3) (Fig. 2). Chewing insects showed a similar response with regard to weight (Fig. 2), but not with respect to diversity and evenness indices (Tables 2 and 3). Non-herbivorous insects did not differentiate between the species when in pure stands. 5. Although there was a significantly greater mean weight of sucking insects in the mixture plots, none of the insect guilds differed significantly among the mixture treatments with respect to the parameters tested (Tables 2 and 3). 6. Results of this study support the C₄ avoidance hypothesis (Caswell et al., 1973), especially with regard to sucking insects. 7. Continued studies investigating plant-insect interaction are discussed.