Influence of host plant abundance and insect diet on the host selection behavior of Maruca testulalis Geyer (Lepidoptera: Pyralidae) and Riptortus dentipes Fab (Hemiptera: Alydidae)

The influence of juvenile nutritional history of two legume pests, the pyralid moth Maruca testulalis (Geyer) and the alydid bug Riptortus dentipes (Fabricius) on host selection by adult and F1 progeny was investigated on cowpea and soybean. Larval counts suggested that juvenile dietary experience in M. testulalis did not influence choice of oviposition substrate by the adults. In screen house experiments, cowpea was always selected over soybean, both by parental adults and F1 larvae, regardless of the larval feeding history. The number of adult moths in the various cowpea and soybean crop combinations was a function of the proportion planted to cowpea; moth distribution was generally unaffected by the area cropped with soybean. The choice of host by adult R. dentipes was also unaffected by the nutritional history of the nymphs. Bug distribution on the two crops varied with crop phenologies; distribution in plots of different cowpea:soybean ratios was a function of the proportion of cowpea in that treatment only when podding occurred earlier on cowpea. However, when podding was synchronized in both crops, there was no distinct preference between the two crops. These results are discussed in the light of the possibility of both pests expanding their host range in Africa to include soybean, or possibly shifting completely from cowpea to soybean.