Overwintering Eggs of the Alfalfa Weevil in Delaware1

Abstract

Studies in 1960 and 1961 in northern Delaware revealed presence of large over-wintering egg populations of the alfalfa weevil, Hypera postica (Gyllenhal). In 1962 and 1963 field cage tests were conducted to evaluate the larval-feeding injury resulting from known numbers of fall and spring-Iaid eggs. These tests showed that t the injury per larva at the average time of first cutting (ca May 20) was highest in those treatments containing all or nearly all fall-laid eggs and lowest in those treatments where all or nearly all spring-laid eggs were added. Field studies in 1964-66, employing cages but depending upon natural egg deposition, further confirmed these findings and indicated that a high percent of the total feeding injury at the time of first cutting can be caused by larvae originating from fall-laid eggs. The injury occurring to alfalfa in northern Delaware does not appear to be solely related to the number of larvae present at the time of first cutting but rather to a combination of factors, including population size, survival rate of the egg and larval stages, cutting time, and especially to the stage of weevil development at this time.