Parasitization of Helicoverpa zea (Lepidoptera: Noctuidae) by Palexorista laxa (Diptera: Tachinidae): Influence of Host Developmental Stage on Host Suitability and Progeny Production

Palexorista laxa (Curran) (Diptera: Tachinidae) successfully parasitized 2nd through 5th instars and prepupal Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae) in the laboratory. Percent successful parasitization (that which resulted in the production of adult parasitoid progeny) increased with host developmental stage, reaching 97% in 5th instars, but fell to 75% in prepupae. The mean number of fly puparia and adults produced per successfully parasitized larva was greatest in 5th instar hosts, reaching 7.8 ± 0.6 (SEM) and 5.5 ± 0.4, respectively. The sex ratio of adult parasitoid progeny per host larval stadium was variable. Host favorability indices were calculated for each host stadium, and was highest in 5th instars. This index allows a direct comparison of the overall impact and reproductive potential of P. laxa attacking hosts of varying developmental stages.