Insect eggs, once oviposited, defend against abiotic and biotic factors using thickness, secretions, or other defenses. The eggs of most insect species are attacked by parasitoid wasps, which are often their most significant mortality factors. The present study is the first investigation of microfilaments as defense from parasitoids. Specifically, the effect of the corn leafhopper Dalbulus maidis DeLong (Hemiptera: Cicadellidae) egg microfilaments against parasitism by Anagrus virlaiTriapitsyn (Hymenoptera: Mymaridae) and Paracentrobia subflava (Girault) (Hymenoptera:Trichogrammatidae) was evaluated. Field and laboratory experiments were conducted to evaluate several biological traits related to parasitism in D. maidis eggs with and without microfilaments. An initial field experiment found no difference in parasitism by A. virlai and P. subflava of eggs with vs. without microfilaments after 5 days of exposure of healthy D. maidis eggs to parasitism. A second field experiment then looked at exposure for 1 day, and this treatment found greater parasitism of healthy D. maidis eggs by each parasitoid species in eggs without microfilaments vs. in eggs with microfilaments. Laboratory experiments conducted separately for A. virlai and P. subflava parasitism after 1 day of exposure to healthy D. maidis eggs confirmed a higher percentage of parasitoid emergence in the eggs without microfilaments (both young and mature eggs) vs. mature eggs with microfilaments. These results suggest that eggs without microfilaments are more parasitized than eggs with microfilaments during a 1-day exposure, but that this difference disappears as egg microfilaments regrow over a 5-day period.

Graphical Abstract