none Hylobius radicis; HYMENOPTERAN-PARASITES; Microctonus pachylobii; New host record & parasite biology notes; WISCONSIN-; Jackson County, Milston; New hymenopteran parasite record & parasite biology notes Microctonus pachylobii; COLEOPTERAN-HOSTS; Hylobius radicis; New host record & biology notes; POPULATION-DYNAMICS; Seasonal occurrence in coleopteran hosts; MORTALITY-; Parasite in coleopteran hosts; POPULATION-SEX-RATIO; WISCONSIN-; Jackson County, Milston; New coleopteran host record & biology notes The endoparasite Microctonus pachylobii was discovered parasitizing a new weevil host, Hylobius radicis. Thirteen of the 154 H. radicis adults collected were parasitized (8.5%). The median numbers of parasites per weevil were 26 ( hivin X = 22.5) during the period April through June, and 4 ( hivin X = 9.4) during August and September. The median male:female sex ratio was 0.91 ( hivin X = 0.65). Males emerged approximately 1 day erlier than females. Median parasite mortality while in the cocoon was 10.2% per parasitized weevil ( hivin X = 11.8%). Microctonus pachylobii was not found parasitizing two previously recorded weevil hosts from field samples, Hylobius rhizophagus and H. pales, and a laboratory study suggests that the parasite may have difficulty parasitizing the latter species.