Pigeonpea, Cajanus cajan (L.) Millsp. (Leguminosae), was found hosting Piezodorus guildinii (Westwood) (Hemiptera: Pentatomidae) in Parana State, Brazil. In the laboratory, nymphs performed better on immature pods of soybean, Glycine max (L.) Merrill (Leguminosae), than on immature pods of pigeonpea. Although nymphs required similar time to complete development, and attained similar weights at adult emergence, mortality was much lower on soybean (57.7%) than on pigeonpea (94.4%). Adult P. guildinii also performed better on soybean than on pigeonpea. Females and males showed similar longevity on both foods, but 34.5% of females oviposited on soybean compared to 10.3% on pigeonpea, with an oviposition delay of 26 days on pigeonpea compared to soybean. Fecundity (eggs/females) was 6.5 greater on soybean than on pigeonpea, and adult body weight gain after 14 and 28 days was 13-23% greater on soybean than on pigeonpea. P. guildinii also showed greater feeding activity on, and greater feeding preference for, soybean than pigeonpea. Bugs colonized soybean during summer and early autumn (January-March), and pigeonpea during autumn, early winter (April-July), and spring (October-November). These results indicate that pigeonpea, although a less preferred and less suitable plant food source of P. guildinii in Brazil, plays an important role to the bug's life history by serving as a temporary host.