Natural biological control of Bagrada hilaris by egg predators and parasitoids in north-central California

Abstract

Bagrada bug, Bagrada hilaris Burmeister (Hemiptera: Pentatomidae), is an invasive stink bug from Asia that has become a major pest of cruciferous crops (Brassicaceae) in California. Conventional insecticides are currently the most effective means for controlling this pest. In organic production, options are limited and generally ineffective. As part of an effort to develop a biological control program for bagrada bug, we documented attack rates by resident parasitoids and predators on sentinel bagrada bug eggs throughout north-central California, including the Salinas Valley, which is the largest cruciferous crop growing region in the US. A total of 51 sites were sampled over three years. Sentinel eggs were placed on the ground, where bagrada bug lays most of its eggs, and in foliage, where all other known stinkbug species deposit their eggs and resident egg parasitoids are most likely to search. Predation rates exceeded 20% per day on some sample dates (averaging 7.2, 7.4 and 6.3% per day in 2017, 2018 and 2019, respectively) and were generally higher on the ground than in the foliage, although temporal patterns were inconsistent and predation levels varied among the sampled regions. Burying eggs in sand did not consistently reduce predation rates, indicating that bagrada bug’s habit of burying its eggs provides only partial protection from predators. Of the 25,387 eggs deployed over the three years of this study that were not predated or missing (out of the 35,673 total eggs that were deployed), only 47 (0.19%) were parasitized. Gryon aetherium Talamas (Scelionidae), a biological control agent for bagrada bug that is currently undergoing testing, was found at one site. Only five of the parasitized sentinel eggs were on the ground, suggesting that few resident parasitoids in north-central California attack bagrada bug eggs, particularly on the ground. These results show that a parasitoid that co-evolved with bagrada bug in its native range is necessary to provide successful biological control of bagrada bug in California.