Radioisotopes—A Potential Means of Evaluating the Host Specificity of Phytophagous Insects

When a single plant of alligatorweed, Alternanthera phylloxeroides (Mart.) Griseb. (Amaranthaceae), was tagged with a 0.5-mc solution of P32 (about 1×10−7M) the radioactive material translocated to the leaves and meristematic tissues via the root system in 48 hours under continuous light. Ten of 26 adult male flea beetles of Agasicles , n. sp., starved 4 hours and then held on the plant for 23 hours at a temperature of 24.7°C, 40% relative humidity and under a 12-hour photoperiod had an average count per minute of 9550. Five of 12 adult alligatorweed thrips, suborder Tubulifera, family Phloeothripidae, n. gen. and n. sp., allowed to feed 69 hours on the same plant beginning 35½ hours after completion of the beetle assay, had an average net count per min of 6460. Although the flea beetle was 87.5 times heavier than the thrips, the thrips ingested 2.13 times more P32 per unit weight after corrections were considered. A separate study of the uptake of the alligatorweed showed that 87.2% of the p32 was absorbed within 54 hours, but the concentration in the tissues of old leaves, young leaves, and meristems differed as much as 6:1.