The preference of Trichopria drosophilae for pupae of Drosophila suzukii is independent of host size

Chromosome-level genome assembly of the bethylid ectoparasitoid wasp Sclerodermus sp. 'alternatusi'

The Bethylidae are the most diverse of Hymenoptera chrysidoid families. As external parasitoids, the bethylids have been widely adopted as biocontrol agents to control insect pests worldwide. Thus far, the genomic information of the family Bethylidae has not been reported yet. In this study, we crystallized into a high-quality chromosome-level genome of ant-like bethylid wasps Sclerodermus sp. 'alternatusi' (Hymenoptera: Bethylidae) using PacBio sequencing as well as Hi-C technology. The assembled S. alternatusi genome was 162.30 Mb in size with a contig N50 size of 3.83 Mb and scaffold N50 size of 11.10 Mb. Totally, 92.85% assembled sequences anchored to 15 pseudo-chromosomes. A total of 10,204 protein-coding genes were annotated, and 23.01 Mb repetitive sequences occupying 14.17% of genome were pinpointed. The BUSCO results showed that 97.9% of the complete core Insecta genes were identified in the genome, while 97.1% in the gene sets. The high-quality genome of S. alternatusi will not only provide valuable genomic information, but also show insights into parasitoid wasp evolution and bio-control application in future studies.

Biological control potential of a laboratory selected generalist parasitoid versus a co-evolved specialist parasitoid against the invasive Drosophila suzukii

A few generations of laboratory selection can increase the developmental success of native parasitoids on invasive targets. However, for this approach to be used more widely for biological control, we need to understand if the improved performance of native species, achieved under artificial laboratory conditions, translates to improved control in more natural environments. It is also unknown what the biocontrol potential of laboratory selected generalist native parasitoids may be compared to co-evolved specialists that are typically introduced for biological control of invasive species. To assess how rearing in artificial diet affected host finding ability in natural hosts, we used laboratory selected (adapted) and nonadapted populations of the generalist native parasitoid Trichopria drosophilae to parasitize the invasive fly, Drosophila suzukii in three different fruit types. In a separate experiment, we compared the effectiveness of adapted and nonadapted populations of T. drosophilae in raspberries with a co-evolved specialist larval parasitoid Ganaspis brasiliensis from Asia that was recently approved for release in the USA. More adult parasitoids emerged in each fruit type of the adapted compared to the nonadapted population of T. drosophilae. D. suzukii emergence rates were reduced on average by 85% by the adapted T. drosophilae population indicating that the artificial rearing conditions did not significantly impair the ability of parasitoids to locate and attack hosts in natural hosts. The specialist G. brasiliensis had higher adult emergence than the adapted population of T. drosophilae; however, both parasitoid species were able to reduce D. suzukii populations to the same extent. These results show that despite the lower developmental success of the laboratory selected T. drosophilae, they killed the same proportion of D. suzukii as G. brasiliensis when host choice was restricted. In nature, where host choices are available, specialist and generalist parasitoids will be unlikely to exhibit the same biocontrol potential.

Effect of Short-Term High-Temperature Stimuli on the Functional Response of Trichopria drosophilae (Matsumura)

Researchers have previously investigated the role of Trichopria drosophilae as a pupal parasitoid in the biological control of Drosophila suzukii in China. Here, we investigated the ability of T. drosophilae to parasitize D. suzukii pupae at different temperatures. To do this, we evaluated the functional response of T. drosophilae to D. suzukii pupae at different temperatures and investigated the specific effects of density on parasitism. The results show that the parasitic functional response of T. drosophilae under different high-temperature stimuli is Holling type II. After processing at 29 °C, the instantaneous search rate was 1.1611; the theoretical maximum parasitic value was 20.88 at 31 °C. The parasitic efficiency decreased with increasing stimulation temperature, as the host pupa density increased from 5 to 25, and the strongest search effect occurred at 0.87 at 27 °C. The searching effect of T. drosophilae at each temperature fell gradually with an increase in prey density from 5 to 25. At 31 °C, the theoretical parasitic maximum of T. drosophilae reached a maximum of 20.88 pupae. At this temperature, when a pair of T. drosophilae was placed in a pupa density of 50, its actual total number of parasites was 18.60.

Below ground efficiency of a parasitic wasp for Drosophila suzukii biocontrol in different soil types

The parasitoid wasp Trichopria drosophilae is promising as a biocontrol agent for controlling the ubiquitous pest Drosophila suzukii (Matsumura). Crucial for the successful implementation of any biocontrol agent is a high parasitisation rate by the parasitoid. Most studies investigating the parasitisation rate of D. suzukii pupae have focused on parasitisation in the fruit or in a petri dish. However, the predominant pupation site of D. suzukii in the field is the soil. Unfortunately, little is known on how well parasitoid wasps can detect and parasitise pupae of D. suzukii buried in the soil. Therefore, we conducted soil parasitisation experiments of T. drosophilae on D. suzukii pupae using two pupation depths in three different soil types (loamy sand, loam, and clay). In all three soil types, we found generally low D. suzukii pupae parasitisation rate by T. drosophilae, independent of the pupation depth. The pupation behaviour of D. suzukii and the parasitisation behaviour of T. drosophilae are discussed in detail. For pest control in most soil types, our results mean that the number of D. suzukii larvae pupating in the soil should be reduced, e.g., by adding a layer of sandy soil or covering the soil with plastic mulch. This might increase the probability of success when using T. drosophilae as a biocontrol agent.

More Power with Flower for the Pupal Parasitoid Trichopria drosophilae: A Candidate for Biological Control of the Spotted Wing Drosophila

Simple Summary

Parasitic wasps are important natural enemies of the spotted wing drosophila, an invasive fruit pest. Releases of mass reared wasps require the presence of all resources necessary to ensure their effectiveness in the crop system. We investigated the utility of floral resources to feed Trichopria drosophilae, one of the candidate species, in a laboratory study. Survival of males and females increased by three to four times when they had access to flowers of buckwheat or of two cultivars of sweet alyssum. The number of offspring produced was also much higher for flower-fed wasps. Given that almost a threefold increase in overall fitness of the wasps was observed, it is advisable to introduce flowering plants into the crop system to enhance their activity for biological control of the spotted wing drosophila. However, any unwanted advantages on the pest itself need to be carefully avoided.

Abstract

Parasitoids are currently considered for biological control of the spotted wing drosophila (SWD) in berry crops. Releases of mass-reared parasitoids require the presence of all resources necessary to ensure their effectiveness in the crop system. The use of floral resources to feed Trichopria drosophilae, one of the candidate species, was investigated in a laboratory study. The life expectancy of males and females increased by three to four times when they had access to flowers of buckwheat or of two cultivars of sweet alyssum. Female realized lifetime fecundity increased from 27 offspring/female exposed to water only to 69 offspring/female exposed to buckwheat flowers. According to this almost threefold increase in parasitoid fitness, it is advisable to introduce flowering plants into the crop system, when parasitoid releases are carried out. Sweet alyssum offers the advantage of not growing too tall in combination with an extended blooming. However, adult SWD were also able to feed on flowers of both plants and survived for at least 27 days, much longer than starving flies. The introduction of flowering plants to promote natural enemies therefore requires further consideration of the risk–benefit balance under field conditions to prevent unintended reinforcement of this pest.