Off-season egg parasitism of the corn leafhopper, Dalbulus maidis: influence of volunteer plants and insecticide-treated seedlings in northern Argentina

Abstract

The corn leafhopper Dalbulus maidis is a key vector of maize stunting pathogens in the Americas. In Argentina, unusually warm and dry winters have enabled the persistence of volunteer maize, potentially bridging seasonal gaps in vector reproduction. This study investigates off-season egg parasitism of D. maidis in volunteer and insecticide-treated maize seedlings. Field and laboratory experiments assessed adult colonization, oviposition, and parasitism rates across four plant treatments. Despite reduced adult survival on treated seedlings, oviposition occurred in all treatments. Volunteer plants exhibited higher egg densities and parasitism rates, particularly in autumn, under post-harvest conditions. The egg parasitoid guild during the maize off-season is composed of four species, with Mymaridae being dominant, and Anagrus virlai emerging as the most prevalent species. These findings demonstrate that egg parasitoids remain active during the off-season and may exploit volunteer maize as a host bridge. The study highlights the ecological importance of conserving parasitoid populations that develop on native vegetation patches harboring alternative hosts during periods when the crop is absent, as well as the unintended consequences of seed-applied insecticides on beneficial arthropods. Although seed treatments could initially reduce parasitism, the developmental requirements of D. maidis eggs (≈236 degree-days) generate a temporal window of exposure in which parasitoids can exploit their host once insecticidal protection declines. Integrating these insights into maize management practices could strengthen biological control and reduce reliance on chemical inputs.