A parasitoid’s decision to reject or accept a potential host is fundamental to its fitness. Superparasitism, in which more than one egg of a given parasitoid species can deposit in a single host, is usually considered sub-optimal in systems where the host is able to support the development of only a single parasitoid. It follows that selection pressure may drive the capacity for parasitoids to recognize parasitized hosts, especially if there is a fitness cost of superparasitism. Here, we used microsatellite studies of two distinct populations of Cotesia vestalis to demonstrate that an egg laid into a diamondback moth (Plutella xylostella) larva that was parasitized by a conspecific parasitoid 10 min, 2 or 6 h previously was as likely to develop and emerge successfully as was the first-laid egg. Consistent with this, a naive parasitoid encountering its first host was equally likely to accept a healthy larva as one parasitized 10 min prior, though handling time of parasitized hosts was extended. For second and third host encounters, parasitized hosts were less readily accepted than healthy larvae. If 12 h elapsed between parasitism events, the second-laid egg was much less likely to develop. Discrimination between parasitized and healthy hosts was evident when females were allowed physical contact with hosts, and healthy hosts were rendered less acceptable by manual injection of parasitoid venom into their hemolymph. Collectively, these results show a limited capacity to discriminate parasitized from healthy larvae despite a viability cost associated with failing to avoid superparasitism.

/pdf/mechanism-and-consequences-for-avoidance-of-superparasitism-3ahswj6tp7.pdf

Mechanism and consequences for avoidance of superparasitism in the solitary parasitoid Cotesia vestalis.

Invasive alien species can act as ‘evolutionary traps’ for indigenous parasites and predators when the alien species is accepted as prey or a host but is unsuitable for consumption or development. We tested the relationship between acceptance and suitability of eggs of the invasive alien Halyomorpha halys (Hemiptera: Pentatomidae) in North America relative to eggs of the indigenous Podisus maculiventris (Pentatomidae) for the indigenous generalist egg parasitoid Telenomus podisi (Hymenoptera: Scelionidae). T. podisi accepted 0–24 h old H. halys eggs at a rate similar to P. maculiventris eggs (87.5 ± 6.0 and 70.2 ± 9.1 %, respectively). Successful development of T. podisi occurred in 98.3 % of attacked P. maculiventris eggs, but was not observed in H. halys eggs. Oviposition by T. podisi did, however, reduce the developmental success of H. halys embryos relative to unattacked controls by 24.1 % in 0–24 h old eggs and 29.6 % in 24–48 h old eggs. We suggest that as H. halys spreads and increases in abundance in North America, it could operate as an evolutionary trap for indigenous egg parasitoids, thereby indirectly causing an increase in population levels of indigenous pentatomids. This predicted indirect effect would be a result of H. halys eggs acting as an egg sink for T. podisi. We also introduce the concept of a ‘time sink’, which may be particularly relevant for parasitoids such as T. podisi that spend considerable time protecting their reproductive investments.

An invasive stink bug as an evolutionary trap for an indigenous egg parasitoid

Parasitoid Sex Ratios and Biological Control

Oviposition behavior, intra- and interspecific host discrimination, and super- and multiparasitism by the scelionids Telenomus busseolae and T. isis were studied using batches of eggs of the noctuid stalk borer Sesamia calamistis as the host. Both Telenomus species were able to discern eggs already parasitized. As a result, self-superparasitism was only 4.0% for T. busseolae and 5.8% for T. isis. Likewise, intraspecific superparasitism was avoided by both species and was significantly higher for T. busseolae than T. isis, and higher when parasitized eggs were offered immediately (0 h) and after 48 h than after 24 h; apparently, the recognition of parasitized eggs at 24 and 48 h was based on the presence of parasitoid larvae rather than a specific marking substance. Multiparasitism was avoided if the female had a choice between unparasitized and parasitized eggs. In a choice experiment, it was 10.2 and 2.5% for T. busseolae and T. isis, respectively. In a nonchoice experiment, multiparasitism did not vary between species and time treatment; it was low, varying between 9.6 and 24.1%. In the 0-h treatment, T. busseolae always outcompeted T. isis, accounting for 63.4 or 91.7% of the offspring, when T. isis or T. busseolae, respectively, was the first species. In the 24-h treatment, the first species emerged more often than the second did but the host egg mortality, i.e., eggs from which neither borer larvae nor parasitoid emerged, was >40%. Whereas T. busseolae is ubiquitous in Africa, T. isis has never been reported from eastern Africa, and it has been proposed for introduction against the prevailing noctuid pest Bussoela fusca. Based on earlier life table and host suitability studies and on the present findings, it is concluded that T. isis would establish in the midaltitudes but not the highlands of eastern Africa.

Self-, Intra-, and Interspecific Host Discrimination in Telenomus busseolae Gahan and T. isis Polaszek (Hymenoptera: Scelionidae), Sympatric Egg Parasitoids of the African Cereal Stem Borer Sesamia calamistis Hampson (Lepidoptera: Noctuidae)

Interspecific competitive interactions can occur either between adult parasitoids searching/exploiting hosts (extrinsic competition) or between parasitoid larvae developing within the same host (intrinsic competition). Understanding how interspecific competition between parasitoids can affect pest suppression is important for improving biological pest control. The purpose of this work was to review both extrinsic and intrinsic competition between egg parasitoid species. These are organisms that are often candidates for biological control programs due to their ability to kill the pest before the crop feeding stage. We first reviewed the literature about interspecific competitive abilities of adult parasitoids in terms of comparative host location strategies highlighting which ecological and behavioral factors are likely to shape extrinsic competition. Then we focused on the interspecific competitive interactions between immatures developing within the same host taking into account which factors play a key role in the outcome of intrinsic competition. Finally we conclude stressing on the need to elucidate the overall competitive interaction that parasitoid species may experience in the field in order to enhance biological control success.

Interspecific extrinsic and intrinsic competitive interactions in egg parasitoids

Ovipositional behavior and host discrimination in three scelionid egg parasitoids of stink bugs

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Ovipositional behavior and host discrimination in three scelionid egg parasitoids of stink bugs