Bagrada Project

Lead scientist: RFH Sforza

Presentation & Context

The painted bug or bagrada, Bagrada hilaris (Burmeister, 1835) (Hemiptera: Pentatomidae), is a pest on Brassicaceae crops worldwide. Since its first introduction in California in 2008, it has become invasive and has now spread to southern US states and beyond to Hawaii, Mexico and Chile. Bagrada bug is native to Africa, the Middle East and Asia where it can sporadically damage local crops in agricultural settings; severe economic losses have been reported when injury occurred during early development of broccoli, cabbage and cauliflower at the seedling stages.

Mating couple of Bagrada hilaris on a caper plant (Pantelleria island, Italy) (Photo by RFH Sforza)

This pest is multivoltine with gregarious behavior. Among stinkbugs, bagrada has a unique oviposition behavior, as it is able to deposit eggs singly into the soil. Surveys for biocontrol agents were conducted in 2015 in Pakistan through collaboration between CABI and ARS. One potential candidate for biocontrol, the egg parasitoid Gryon aetherium (formerly G. gonikopalense) (Hymenoptera, Scelionidae) was received at EBCL and is routinely maintained since.

A female Gryon aetherium parasitizing a bagrada egg covered with sand particles collected from our
permanent rearing in the EBCL quarantine facility (Photo by RFH Sforza)

Research components

Foreign exploration/biological traits of Bagrada hilaris and Gryon aetherium/Sterile Insect Technique

Under laboratory conditions, this parasitoid completes development in 25 days and females can produce up to 60 progeny on average. Beyond its reproductive capacities and its high longevity, its major advantage is its ability to detect and parasitize buried eggs of bagrada. Pentatomid stinkbugs usually deposit clustered eggs on their host plants. As an exception, the phytophagous pest Bagrada buries single eggs in the ground. We then aimed to evaluate the capacity of G. aetherium to respond to the original bagrada ovipositional behavior. Our results showed that G. aetherium exhibits a well-adapted foraging behavior observed by tracing and successfully parasitizing 2mm-deep buried bagrada eggs, which was further supported by video recordings. Four conditions of egg detectability and foraging duration were tested. After 2 hours, 71% of tested parasitoids succeeded, and after 72 hours 100% of them succeeded. Our data suggested that host egg detection was based on chemical cues since parasitism success was reduced by up to 20% when eggs were manually buried under a clean substrate (without chemicals) or a substrate previously used for oviposition but disturbed. Evidently, G. aetherium is able to overcome both the egg detection and physical barrier constituted by the sand to parasitize the pest, though fitness limitations must be considered.

Since 2016, EBCL has conducted surveys in Kenya and South Africa to study the native biodiversity of bagrada egg parasitoids using "classical" sentinel eggs. We plan to investigate development of a new “prototype” for sentinel eggs. In this project, derived from the mating of irradiated males with virgin females, the overall idea is to use the Sterile Insect Technique (SIT) to produce eggs to be used in the field as new natural (but sterile) substrate for egg-parasitoid oviposition and larval development. Sentinel eggs can be associated with classical biological control as they allow discovery of new native and resident parasitoids and improve the monitoring of dispersal of new biocontrol agents in a new environment, without introducing viable stink bugs. A preliminary phylogeography study suggested Pakistan as a source population for invasive Bagrada in North America.

Field work in South Africa to collect bagrada from wild Brassicas in Citrus orchard (Photo by RFH Sforza)

Students involved

Martel (PhD, 2017-21), M. Ponchon (Master2, 2018), F. Scirpoli (Master2, 2019-20)

Selected recent publications

Martel & Sforza 2023. Biological Control

Cristofaro et al. 2022. Insects

Martel & Sforza 2021. Biological Control

Martel, Scirpoli & Sforza 2021. Entomologia Generalis

Martel & Sforza 2021. Journal of Pest Science

Conti et al. 2020. Entomologia Experimentalis et Applicata.