Search

The lineage G1 of Ganaspis brasiliensis is a larval parasitoid of the worldwide pest Drosophila suzukii and one of its most effective natural enemies in the native area. Because of its high degree of host specificity, G. brasiliensis G1 is considered a suitable species for introduction in areas invaded by D. suzukii following a classical biological control approach. Indeed, the release of the parasitoid is currently implemented in the USA and Italy. G1 females attack only host larvae developing in ripening fresh fruits on the plant and not larvae that develop in decaying fruits. To date, virtually no information is available on the cues regulating the foraging behavior of G1. In this study, we therefore aimed to find out whether chemical cues are exploited by G1 females to: (i) locate host fruits; (ii) locate suitable host larvae within infested fruit; (iii) discriminate between infested fresh fruits and infested rotting ones. We used a model system composed of blueberries and D. suzukii tested in two-choice olfactometer bioassays (with D. suzukii-infested fruits, healthy fruits, and pure air as odor targets), followed by the collection and the characterization of volatile organic compounds (VOCs) released by the tested targets. The results showed a clear time-dependent choice made by G1 females of infested versus healthy fruits related to the concomitant development of D. suzukii larvae and fruit degradation. Attraction to infested fruits was recorded during the early stages of infestation, followed by a repellent phase coinciding with fruits largely degraded by larval feeding. We found that the attractiveness of G. brasiliensis G1 towards fruits infested by young larvae was associated with the detection of VOCs released by the infested blueberries, and host’s cuticular hydrocarbons. Conversely, the repellence of older and deteriorated fruits hosting developed D. suzukii larvae was associated with the detection of a fermentation compound produced by microorganisms likely carried inside the fruit by the flies. The response of G1 females to the temporal dynamics of chemical cues emitted by the fruit–host larvae complex was consistent with the high degree of specificity of the parasitoid towards the ripening host fruits and towards D. suzukii.

[Display omitted] • Ganaspis brasiliensis G1 is a larval parasitoid highly specific to Drosophila suzukii. • G. brasiliensis G1 females attack only young host larvae in ripening fruits. • VOCs from blueberries infested by young host larvae attract G1 females. • VOCs from blueberries deteriorated by developing host larvae are repellent to G1 females. • VOCs emitted by uninfested ripe fruits are not attractive towards G1 females. The lineage G1 of Ganaspis brasiliensis is a larval parasitoid of the worldwide pest Drosophila suzukii and one of its most effective natural enemies in the native area. Because of its high degree of host specificity, G. brasiliensis G1 is considered a suitable species for introduction in areas invaded by D. suzukii following a classical biological control approach. Indeed, the release of the parasitoid is currently implemented in the USA and Italy. G1 females attack only host larvae developing in ripening fresh fruits on the plant and not larvae that develop in decaying fruits. To date, virtually no information is available on the cues regulating the foraging behavior of G1. In this study, we therefore aimed to find out whether chemical cues are exploited by G1 females to: (i) locate host fruits; (ii) locate suitable host larvae within infested fruit; (iii) discriminate between infested fresh fruits and infested rotting ones. We used a model system composed of blueberries and D. suzukii tested in two-choice olfactometer bioassays (with D. suzukii -infested fruits, healthy fruits, and pure air as odor targets), followed by the collection and the characterization of volatile organic compounds (VOCs) released by the tested targets. The results showed a clear time-dependent choice made by G1 females of infested versus healthy fruits related to the concomitant development of D. suzukii larvae and fruit degradation. Attraction to infested fruits was recorded during the early stages of infestation, followed by a repellent phase coinciding with fruits largely degraded by larval feeding. We found that the attractiveness of G. brasiliensis G1 towards fruits infested by young larvae was associated with the detection of VOCs released by the infested blueberries, and host's cuticular hydrocarbons. Conversely, the repellence of older and deteriorated fruits hosting developed D. suzukii larvae was associated with the detection of a fermentation compound produced by microorganisms likely carried inside the fruit by the flies. The response of G1 females to the temporal dynamics of chemical cues emitted by the fruit–host larvae complex was consistent with the high degree of specificity of the parasitoid towards the ripening host fruits and towards D. suzukii. [ABSTRACT FROM AUTHOR]

• Adult parasitoids freely searched for hosts under up to 150 cm of chickpeas. • Parasitoids kept bruchid populations below 10% that of the control. • Parasitoid wasps can be an alternative to pesticides for controlling C. chinensis. In this study, two predatory mites and two parasitoid wasps were evaluated for their effectiveness in controlling Callosobruchus chinensis (Coleoptera: Chrysomelidae), a common pest in stored chickpeas. The predatory mite Amblyseius swirskii (Acari: Phytoseiidae) preyed on the bruchid's eggs but did not consume a large amount; the mite Blattisocius tarsalis (Acari: Ascidae) did not consume C. chinensis eggs. However, the larval parasitoids Anisopteromalus calandrae and Lariophagus distinguendus (Hymenoptera: Pteromalidae) were effective at reducing the bruchid's larval population, producing mortality rates above 90% in controlled conditions (28 ± 2 °C, 75 ± 5% relative humidity [RH]). In tubes of 20-cm diameter filled with 9–35 kg of chickpeas, both parasitoids were able to parasitize the host at depths of 40, 100, and 150 cm, even when larvae were offered simultaneously at all depths. This indicates that parasitoids will probably be able to locate hosts at least at 150 cm of distance in a storage facility. A. calandrae was similarly effective at reducing the bruchid population at different parasitoid-to-host ratios (1:7, 1:15, 1:30, and 1:60). Moreover, A. calandrae efficiently reduced C. chinensis populations when released in 25-kg commercial polypropylene bags of chickpeas in simulated warehouse conditions (27 ± 2 °C and 65 ± 4% RH). This is the first time that A. calandrae and L. distinguendus are shown to be effective biological control agents for the integrated management of C. chinensis in stored chickpeas and can be an alternative to the application of pesticides for maintaining low bruchid population levels. [ABSTRACT FROM AUTHOR]