Trouble comes in pairs: Invasive stink bugs in California

Worldwide, stink bugs are an economically important insect group that can be injurious to food crops. California (CA) has more than 70 stink bug species, a mixture of non-native and native species (Froeschner 1988; Lara et al. 2016). Among the non-natives are bagrada bug (BB; Bagrada hilaris) and brown marmorated stink bug (BMSB; Halyomorpha halys). Their invasion into CA poses a considerable threat to the state’s specialty crop production and has triggered the development of pest management programs. Both stink bugs use their needle-like mouthparts to pierce and feed on plants and fruit, which may cause economic damage. With respect to BMSB and BB, there are notable differences and similarities in their invasion ecology which have influenced management programs in CA. BB was first detected in the U.S. in CA (Los Angeles County) during 2008 and follow-up DNA analyses indicate CA populations originated from Pakistan (Reed et al. 2013; Sforza et al. 2017). In the U.S., BB has been recorded on 32 host plants from 8 families (Bundy et al. 2018). However, BB is mainly a pest threat to cultivated cole crops (Brassicaceae), including broccoli, cauliflower, cabbage, and kale. Feeding damage from BB causes stunted/malformed vegetative growth, wilting, and stippling (Fig 1). Severe damage symptoms from BB feeding, leading to plant death, are commonly observed with direct-seeded cole crops. BB’s distribution in the U.S. is limited to southwestern states (CA, AZ, NV, NM, TX, and UT) and it thrives in warm climates, more so than BMSB. BB’s current CA distribution ranges from Imperial Valley to parts of the Sacramento Valley, for a total of 22 invaded CA counties (Bundy et al. 2018). In CA, BB has peak activity occurring in spring and fall months, coinciding with the cole crop field season in agricultural areas in the state (Reed et al. 2013). It is estimated that during 2010-2014 BB generated >10% stand losses and plant injury to commercial broccoli crops in AZ and CA (Bundy et al. 2018).