Age- and Density-Dependent Parasitism Rate and Development Time of the Generalist Egg-Parasitoid Ooencyrtus telenomicida (Hymenoptera: Encyrtidae) on Eggs of the Brown Marmorated Stink Bug, Halyomorpha halys

Simple Summary The brown marmorated stink bug, Halyomorpha halys, is a pentatomid bug that feeds on a wide range of economically important crops. Crop protection in newly invaded areas mainly relies on the use of broad-spectrum chemical insecticides, while little to no information is available regarding a classical biological control approach. The overall purpose of the present study was to estimate the parasitism rate and development time of the native egg parasitoid Ooencyrtus telenomicida Vassiliev (Hymenoptera: Encyrtidae) when offered H. halys egg-masses, taking into consideration several parameters. Specifically, we tested different parasitoid ages and densities on 1–4-day-old H. halys eggs. According to our results, parasitoid density and the age of host eggs significantly affected the parasitism rate of O. telenomicida. High parasitoid density along with younger host eggs led to higher parasitism rates. Likewise, a significant interaction was observed between the parasitoid density and their age. Successful parasitisation occurred with host eggs up to 4 days old, with parasitism rates decreasing as host egg age increased. A three-fold higher parasitism rate of H. halys eggs was observed when they were parasitised by older O. telenomicida females, compared to younger ones. Concerning the development time of O. telenomicida, individuals that developed in younger host eggs displayed a shorter development time. Parasitoid age did not affect the development time of O. telenomicida, nor did the density of parasitoids. Abstract Halyomorpha halys (Hemiptera: Pentatomidae) is an invasive pest species that was imported into Greece in 2011 and since then, has caused severe qualitative and quantitative damage to economically important crops. Its management relies mainly on the use of broad-spectrum insecticides, with little to no information available concerning the potential use of native parasitoids in terms of classical biological control. Our study aimed to assess the parasitism rate and development time of the gregarious egg parasitoid Ooencyrtus telenomicida (Hymenoptera: Encyrtidae) on H. halys egg-masses, depending on several factors such as: (i) age of parasitoids, (ii) density of parasitoids, (iii) age of host eggs, and (iv) oviposition experience of parasitoids. According to our results, the younger the host eggs and the more parasitoids, the higher the parasitism rate achieved by adults of O. telenomicida, with the maximum mean value of the parasitism rate observed with 1-day-old host eggs and 4 parasitoid pairs (57.3%). On the contrary, the lowest mean value of the parasitism rate was observed with 4-day-old host eggs and 1 parasitoid pair (6.5%). Similarly, the age of parasitoids significantly affected parasitisation. The older the parasitoids were, the higher the parasitism rate achieved by adults of O. telenomicida, with a three-fold higher parasitism rate observed at 3–4 and 5–6-day-old O. telenomicida, compared to 1–2-day-old (31.8, 32.4, and 12.1%, respectively). Individuals that developed in younger host eggs displayed a shorter development time, and the shortest development time was observed for O. telenomicida laid by 2 parasitoid pairs. Parasitoid age did not affect the development time of O. telenomicida, although there was a tendency for individuals laid by younger female parasitoids to exhibit a shorter development time. Our findings provide valuable information on the potential use of O. telenomicida as a biocontrol agent of H. halys.