New insights into predation through imaging

Authors: PICKETT, CHARLES - California Department Of Food And Agriculture; BORKENT, CHRISTOPHER - California Department Of Food And Agriculture; POPESCU, VIOLA - California Department Of Food And Agriculture; LIGHTLE, DANI - Oregon State University; Hogg, Brian; GRETTENBERGER, IAN - University Of California, Davis

Submitted to: Biocontrol Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/1/2021
Publication Date: 10/20/2021
Citation: Pickett, C.H., Borkent, C.J., Popescu, V., Lightle, D., Hogg, B.N., Grettenberger, I.M. 2021. New insights into predation through imaging. Biocontrol Science and Technology. 32(2):196-222. https://doi.org/10.1080/09583157.2021.1990856.
DOI: https://doi.org/10.1080/09583157.2021.1990856

Interpretive Summary: Although predators can help in controlling agricultural pests, their impacts can be difficult to measure, especially if they are active at night. We used field cameras to observe and identify predators attacking eggs of brown marmorated stink bug and bagrada bug, two damaging stinkbug pests that have spread throughout California. A field camera helped to identify the predators attacking the eggs of these pests, and allowed the impacts of different predators to be measured. Predation of bagrada bug eggs, which are laid in soil, was much greater than for eggs of brown marmorated stink bug, which lay their eggs in the foliage of plants. Predators that attacked brown marmorated stink bug eggs included beetles, various species of earwigs, cockroaches and spiders. The most important predators of bagrada bug eggs were two ant species and springtails (Collembola). We found that spiders and ants caused more damage to brown marmorated stink bug eggs when they were acting together than when they were on their own. The importance of springtails as a predator of bagrada bug eggs was also surprising, because these insects are usually scavengers.

Technical Abstract: The role of generalist natural enemies has long been considered an important component of mortality for many agricultural pests, but can be difficult to quantify. This is due largely to the difficulty in their identification. We present the use of digital imaging along with sentinel egg cards as a means of both identifying key stink bug egg predators and measuring their relative impact on egg survivorship. Two exotic, invasive stink bug species have recently entered California. Brown marmorated stink bug (BMSB), Halyomorpha halys, and bagrada bug, bagrada hilaris, are now spreading throughout the state and represent serious pests to production agriculture. As part of an effort to introduce specialized egg parasitoids for each of these stink bug species, a statewide survey was conducted to identify resident natural enemies of their eggs. A field camera aided in the identification of arthropods attacking these eggs, sometimes to the species level, and in the quantification of the relative impact each had on the eggs. Predation of bagrada bug eggs, which are naturally oviposited into the soil, was much greater than for eggs of BMSB, which oviposit like most stink bugs onto the foliage of plants. The top ranked morphotaxa of predators of BMSB were the carabid Laemostenus complanatus, two species of earwigs, the European earwig Forficula auricularia and ring legged earwig Euborellia annulipes, the oriental cockroach Blatta orientalis, and the spider Trachelas spp. most likely pacificus. The two most common and important morphotaxa predators of bagrada bug were two ant species, Solenopsis xyloni and Monomorium ergatogyna, and Collembola. Two activity indices were developed to rank and compare these predators, one based on contact time plus predation efficiency, the second based entirely on the frequency of visits that included egg contact. Two striking, unanticipated results are also reported: an apparent synergistic interaction between Trachelas spp. and the native ant Monomorium ergatogyna in causing damage to sentinel eggs of BMSB, and the predaceous role for Collembola on bagrada bug sentinel eggs. These results highlight the importance of imaging in characterizing the role of arthropod predators in suppressing agricultural pests.