Trade-offs between developmental parameters of two endoparasitoids developing in different instars of the same host species

Trade-offs amongst life history traits is a major theme in evolutionary biology. Parasitoid wasps are important biological control agents and make excellent organisms to examine trade-offs in fitness related traits such as size, development rate and survival. Here, we examined trait-related trade-offs in 2 solitary endoparasitoids developing in different stages (or instars) of the same caterpillar host, the cabbage moth Mamestra brassicae. Microplitis mediator is a small specialist parasitoid that attacks first (L1) to third (L3) instars of M. brassicae; Meteorus pulchricornis is a larger highly generalized parasitoid that attacks L1-L4 instars of the same host species. When developing in early host instars (e.g. L1-L2), both parasitoids differently traded-off size against development time. In M. mediator, adult body mass was smaller in wasps developing in L1 than in L2 and L3 hosts, whereas development time was unaffected by instar. By contrast, adult body mass in M. pulchricornis was smaller and development time longer when developing in L1 and L2 than in L3 and L4 instars. Periodic starvation of M. brassicae caterpillars parasitized by M. pulchricornis further reduced adult mass and extended development time of wasps in L2 (but not L4) hosts. Maximum egg load in M. pulchricornis (but not M. mediator) was correlated with adult female body size. Our results imply that rapid development time is more important than body size for fitness in both species, although in M. pulchricornis both development time and adult size are traded off in determining the optimal phenotype. Developing a better understanding of association-specific patterns of development in parasitoids can assist in the optimization of mass rearing of these insects for biological control. © 2014 Elsevier Inc

Development of two related endoparasitoids in larvae of the diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae)

We compare the growth and development of two related solitary endoparasitoids (Braconidae, Microgastinae) in different instars (second and third) of the diamondback moth Plutella xylostella. Cotesia vestalis is a well-studied parasitoid whose larvae feed primarily on host hemolymph and fat body whereas Dolichogenidea sicaria is a parasitoid whose larvae consume the entire host caterpillar before pupation. Little is known about the biology of D. sicaria including its association with P. xylostella. When developing in L2 and L3 host instars, survival of both parasitoids to adult was similar. However, development time was longer in D. sicaria than in C. vestalis but the adult wasps were also larger. Both species were protandrous and exhibit sexual size dimorphism, where females were the larger sex. Our results suggest that D. sicaria is a promising new biological control agent of P. xylostella, augmenting better studied parasitoids such as C. vestalis

The cabbage moth or the sorrel moth (Lepidoptera: Noctuidae)?

When insect herbivores develop over many generations on the same plant species, their descendants may evolve physiological adaptations that enable them to develop more successfully on that plant species than naive conspecifics. Here, we compared development of wild and lab-reared caterpillars of the cabbage moth, Mamestra brassicae, on a cultivar of cabbage Brassica oleracea (cv. Cyrus) and on a wild plant species, sorrel, Rumex acetosa, on which the wild strain had been collected and reared for two earlier consecutive generations. The lab strain had been reared on the same cabbage cultivar for more than 20 years representing > 200 generations. Survival to adult did not vary with strain or plant species. Both strains, however, developed significantly faster when reared on R. acetosa than B. oleracea. Pupae from the field strain were larger when reared on B. oleracea than on R. acetosa, whereas the identity of the plant species did not matter for the lab strain. Our results show that long-term rearing history on cabbage had little or no effect on M. brassicae performance, suggesting that some generalist herbivores can readily exploit novel plants that may be chemically very different from those on which they have long been intimately associated

Short-term seasonal habitat facilitation mediated by an insect herbivore

In nature some organisms may facilitate others by creating shelter or other niches that they use for variable periods. We describe a natural multitrophic-species complex in the Netherlands involving a plant, the common hogweed (Heracleum sphondylium) a specialist chewing herbivore, the parsnip webworm (Depressaria pastinacella) and various arthropods associated with them. Larvae of D. pastinacella feed on H. sphondylium seeds and, after they have finished feeding, chew holes in the hollow stems where they pupate. In some areas of the country almost 50% of plants are attacked by webworms. The holes are used by other arthropods to gain access to the stems including herbivores, omnivores, predators and decomposers. The duration of plant occupancy varies between 3 and 4 months, until the plants die. Plants without moth-produced holes were always free of other arthropods, whereas plants with holes, in addition to pupae (and/or mummified-parasitized webworm larvae), often contained many woodlice, earwigs and/or spiders. Earwigs and woodlice perform important ecological functions as predators (in orchards) and decomposers respectively. Our results show that the simple biological activity of one herbivore species can have at least short-term effects on the local arthropod community. In der Natur können manche Organismen andere begünstigen, indem sie Refugien oder andere Nischen erschaffen, die sie für unterschiedliche Zeiträume nutzen. Wir beschreiben einen natürlichen multitrophischen Artenkomplex in den Niederlanden, der den Wiesen-Bärenklau (Heracleum sphondylium), die Pastinakmotte (Depressaria pastinacella) und verschiedene mit ihnen assoziierte Arthropoden umfasst. Die Larven der Pastinakmotte fressen an Bärenklausamen und beißen später Löcher in die hohlen Stengel, um sich darin zu verpuppen. Die Löcher werden von anderen Arthropoden genutzt, um Zugang ins Stengelinnere zu erhalten. Die Pflanze wird für etwa drei bis vier Monate besiedelt bis sie abstirbt. Pflanzen ohne Mottenlöcher wurden niemals von anderen Arthropoden besiedelt, während Stengel mit Löchern zusätzlich zu den Mottenpuppen bzw. parasitierten Larvenmumien häufig viele Asseln, Ohrwürmer und/oder Spinnen enthielten. Ohrwürmer und Asseln erfüllen wichtige ökologische Funktionen als Räuber in Obstplantagen bzw. als Zersetzer. Unsere Ergebnisse zeigen, dass die einfache biologische Aktivität einer Herbivorenart zumindest kurzfristige Auswirkungen auf die lokale Arthropodengemeinschaft haben kann

Convergent development of a parasitoid wasp on three host species with differing mass and growth potential.

Plant science

Convergent development of a parasitoid wasp on three host species with differing mass and growth potential

Article / Letter to editorInstituut Biologie Leide