If you search for the brown stink bug species Euschistus rugifer in iNaturalist, you won't find much; indeed, zero observations entered in the US. Similarly, an entry on BugGuide.net has little more than a few images of a specimen and its structure. Elsewhere, it seems the species is described primarily in literature out of Latin America (ref. Artropodos de Chamela. edited by Alfonso N. García Aldrete, Barajas Ricardo Ayala, 2004). Yet it seems the range of this species may soon include the US, traveling into the country on board shipments of agricultural products. Several news accounts mention records from San Francisco (2014), Arizona and the Rio Grande Valley of Texas, but perhaps the most dramatic is the identification of insects found in a Customs seizure at Dallas-Fort Worth Regional Airport just this month, strikingly far inland for a new incursion. Information on the life history of this species (in English sources, at any rate) is also scarce, but it would seem E. rugifer has a fondness for culinary herbs. As always seems to be the case, humans in movement and the goods that accompany them are the main means of transport for this potential pest, with small teams of inspectors at points of entry being the nation's only defense.

Ref. "CBP Dallas Discovers Harmful Stinkbug" https://www.cbp.gov/newsroom/local-media-release/cbp-dallas-discovers-harmful-stinkbug#:~:text=“CBP%20agriculture%20specialists%20are%20highly,each%20day%20is%20so%20important.

"Crop-Eating Stinkbug Found on Basil at San Francisco Airport; 1st for Bay Area" https://www.nbcbayarea.com/news/local/crop-eating-stinkbug-found-on-basil-at-san-francisco-airport-1st-for-bay-area/75321/

Observations of this stink bug species continue to accumulate, raising questions about why this insect is in the SoCal region now, and what its impact might be. Last Fall, the CA Department of Food and Agriculture posted a draft pest rating for the species, applying criteria that (at least for now) classify this insect as Low Risk, and proposing an overall Pest Rating of C. Read the complete draft, with natural history notes, at: https://blogs.cdfa.ca.gov/Section3162/?p=9206

Finding other references on the life history of P stictica (at least for English language publications) can present a challenge, though a recent paper from Brazil suggests these insects may utilize plants in the genus Senna as habitat and food source. While only a few iNat observers happen to note plant species associated with the occurrences of P.stictica nymphs or adults, where plants are identified they often seem to involve species related to Senna (in the Subamily Caesalpinioideae, e.g. Parkinsonia and Cassia), plus some other pod-bearing plants (such as the orchid tree Bauhinia, also a legume). The first occurrence of P.stictica in the US (1984) was collected in Texas off citrus. Some iNat records seem to show the insects on Ligustrum (privet); the Brazilian authors made similar observations, but when they tried raising a test sample of the insects on privet berries they reported little success.

Generally speaking, all the above mentioned plant types are prevalent throughout Southern California, but so far this doesn’t seem to tell us much about why P.stictica came to - or how it might have been transported around - the region. Whether iNat observations give us an altogether accurate timeline for the appearance of P.stictica remains to be verified, but the vast majority of the observations would seem to be unique (non-recurring) records. The first in the posted sequence come from late 2019, with only occasional sightings until a rapid increase began in August 2021. Of the 846 iNat observations of P. stictica in the Americas since February 2012, as of this writing 112 have posted locations for Southern California.

Ref: Panizzi, Antônio Ricardo & Grazia, Jocélia, 2001, Stink Bugs (Heteroptera, Pentatomidae) And An Unique Host Plant In The Brazilian Subtropics. Iheringia, Sér. Zool. 90, pp. 21-35: 26-28 https://treatment.plazi.org/GgServer/html/03F3E608FF9CFD73FE45C2D0259B2A4F

Pellaea stictica - a rather attractive and distinctive stinkbug species - seems to have experienced a spike in occurrences throughout SoCal during the past 6 months or so. In fact, it appears the first SoCal record of the species in iNaturalist comes from as recently as 2019. P. stictica is widespread and apparently very well known throughout Latin America, particularly in South America, and may well be on its way to being more common in the southern US. (Its first record in Texas was as recent as 1984.) The life history of the species available (in English, at least) via the internet is pretty sparse: some sources describe the species as an inhabitant of rocky canyons. Individuals of the species can be quite numerous at times, and may frequent plants in the nightshade family (Solanaceae) as well privet (Ligustrum), suggesting expansion in the US could be related to the transportation of landscaping plants.

References:
New data on Pellaea stictica Dallas (Heteroptera: Pentatomidae) in South America. Mariom A. Carvajal, Catalina J. Vargas and Eduardo I. Faúndez. Revista Chilena de Entomología (2019) 45 (3): 419-424. https://www.researchgate.net/publication/335058295_New_data_on_Pellaea_stictica_Dallas_Heteroptera_Pentatomidae_in_South_America

New United States Records For Two Heteroptera: Pellaea stictica (Pentatomidae) And Rhinacloa pallidipes (Miridae).
Thomas J.Henry. Proc. Entomol. Soc. Wash. 86(3),1984,Pp.519-520 https://research.amnh.org/pbi/library/0863.pdf

Thank you to observers @danielleruais , @mooseandsquirrel, @silversea_starsong and others for putting this project "over the top" in recent weeks! Harlequin bug still reigns supreme as the most observed stinkbug species in SoCal, with this August being the busiest month so far for the project's site: 208 new observations from 115 individual observers. Should extensive moisture return to the state in the near future, it will be interesting to see how the Pentatomid diversity responds.

As this project approaches 6000 total observations, it is worth noting that of the over 4000 research grade observations, of the top five most frequently observed species, three were brought to North America by humans. The fourth of these species (Nezara viridula) typically goes by the generic-sounding common name of “Southern green stink bug”, though there’s actually nothing terribly “southern” about the species. It’s now found far outside what might have been its native setting (probably East Africa), and has what amounts to a global distribution, though (like with BMSB) its occurrences seem to coincide with human population centers. While N. viridula doesn’t seem to concentrate in numbers as would a nuisance pest species, it occurs to a sufficient extent - and has a big enough appetite - to be a significant plant pest.

Like Pentatomidae in general, N. viridula thrives in part due to its chemical defense, which has been analyzed to contain a cocktail of at least seven organic compounds (ref. Secret Weapons, Eisner et. al. 2005). This isn’t to say it’s invulnerable: apparently, a parasitic wasp imported to the US (Trissolcus basalis) locates Nazara’s eggs by following the traces of these chemicals; a native species of tachnid fly (Trichopoda pennipes) is unaffected by the stink bug’s defenses, and follows the “scent” of the bug’s pheromones in order to parasitize the adults. Despite these depredations, Nezara viridula persists among California’s tomato and bean crops.

Throughout this project, two species appear to be inextricably linked: harlequin bug and bladderpod. A general search through various references failed to turn up many specific mentions of the relationship between these organisms. It doesn’t help that the taxonomy of the plant remains a rather unsettled question. For iNaturalist users, the specific reference is currently Peritoma arborea, yet many other current references (Encyclopedia of Life, USDA Plants) use the epithet Cleome isomeris, and older publications use the binomial Isomeris arborea. The common names of the plant are also numerous, and include burro fat, spiderflower, and “skunk among plants” (referencing its unpleasant odor).

Bladderpod and its closest relatives are found over a good deal of the western US, but the range of Peritoma arborea/Cleome isomeris is restricted to Southern and Baja California and parts of western Arizona. Within that range it provides vital habitat for at least two insect species: the harlequin bug and Becker’s white butterfly (Pontia beckerii). For the butterfly, bladderpod is an important larval food. In the case of the harlequin, this insect’s entire lifecycle can take place on a single bush.

Outside of the range of bladderpod, these two insects will defer to other plants for sustenance (primarily closely related species of the mustard family), yet bladderpod appears to be especially adept at maintaining the harlequin bug in settings close to people. This may well be attributable the fact that the plant is notably wildfire resistant. So while ever more frequent fires make the SoCal landscape more biologically monotonous, Peritoma arborea (or whatever) continues to provide habitat for our most frequently observed stink bug.

Ref. Bowers, J.E., Shrubs and Trees of the Southwest Deserts (1993) Southwest Parks and Monuments Assoc.

Of all the medium-sized insects that inhabit Southern California, stinkbugs might be the most frequently overlooked…or perhaps more accurately, ignored. Back in 2014, when UC-Riverside entomologist Mark Hoddle and I brainstormed this project, we were interested to see if citizen science might be a way to get a better track on what one species of stinkbug - Halyomorpha halys (the brown marmorated stinkbug) - might be doing this part of the state. At that same time, we thought people would also find other species of stinkbug easy to spot, harmless, and even amusing.

An introduced species that had proven to be a huge nuisance in the eastern US, H. halys (BMSB) was beginning to be established in SoCal, but how extensive would be its distribution? What might be its impact on other Pentatomid species? At this point, almost 2000 iNaturalist users have recorded upwards of 50 stinkbug species in Southern California, occurrences from north of Point Concepcion south to the Tijuana area; from the Imperial Sand Dunes to the southernmost Sierras. By this record, the distribution of BMSB is still fairly restricted, to the greater Los Angeles area with some occurrences in San Diego County. This largely follows the spread of two other introduced species, Bagrada bug and African cluster bug, to the degree that one could conclude that such introduced Pentatomids follow intense human movement and development pretty closely.

By comparison, native species of stinkbug are still seen frequently and over large areas. The flamboyantly-marked harlequin bug is sighted most often (especially in coastal areas associated with habitat of the bladder-pod plant), but stinkbugs of the genus of Thyanta have shown the largest distribution, from mountains to deserts to the coast, in many cases following the distribution of agricultural lands. (T. pallidovirens is apparently a pest of California’s pistachio crops.)

Is there any reason to be thankful to invasive stink bugs?
To be sure, the proliferation of species like Bagrada hilaris and Halyomorpha halys has been a disaster on many levels, but one thing these invasions have accomplished is to direct a great deal more interest toward the Pentatomidae. A casual Internet search or two on the topic of stink bugs, their behavior, impacts, and even simply on their “stink” reveals a wide diversity of new publications - popular and scientific- regarding these insects. Never mind that many websites (especially those based in the eastern US) describe the BMSB as “the most common stink bug”, to their credit these sites have typically gone to some lengths to describe pentatomids, their physical and behavioral features, and even their roles in the environment. More remarkable are the newer findings with respect to the chemicals manufactured and exuded by these insects: not simply their obvious defensive properties, but also their functions as chemical attractants, even the anti fungal and antimicrobial properties apparent in these substances. For an example, see https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5027987/

Over the past several months, there's been what you might call an "outbreak of hope" with regard to introduced species, and including the Brown Marmorated Stink Bug. Some have hypothesized that the violent, cold winter in a good deal of the US this year might spell "curtains" for species introduced from warmer climes, organisms that may lack the adaptations to survive the cold months in North America. This hopeful scenario has been addressed with a good deal of skepticism, in that many insects have a "superpower" for over wintering, a physiological trait known as "vitrification". In this instance the sugars and proteins in an insect's bodily fluids prevent the formation of ice crystals at below-freezing temps; these fluids become glass-like, or "vitrified". Whether any or all of our introduced, outdoor insect pests have this ability may be something we know soon enough. Meantime, laboratory entomologists have been working to find biocontrol weapons (species that kill the pests). In the case of the BMSB, efforts to implement a parasitic wasp species from Asia are looking promising. Stay tuned, and please read this brief report:: https://www.kqed.org/science/1937639/samurai-wasps-say-smell-ya-later-stink-bugs?utm_source=facebook&utm_medium=social&utm_content=pubmedia&utm_campaign=DL_stinkbugs&fbclid=IwAR0DRjWvF34LV3TFWOpr4x_bzhGR1FYu99pqIr5P3GdusM_tdr-8Qf0Kc2s

Though I've been away from this project for a while, it's heartening to see the observations continue to accumulate (approaching 2000 at this writing) as well as the number of members and unique observers (almost 700) continue to grow. The goals of the project have not changed: to track the distribution of introduced pest species (eg. bagrada bug) in SoCal while painting an evolving picture of Pentatomid distribution, diversity and behavior. However, in the years since the project began, the significance of monitoring what are typically innocuous and overlooked insects has increased.

The alarm over the disappearance of common insects has grown steadily, from fairly informal observances to what now is becoming a quantifiable and reproducible determination. Most recently, a report coming out of the Proceedings of the National Academy of Sciences documents not only a striking loss in insect diversity, but a concomitant loss in numbers and diversity on up through the food chain. (See the paper at http://www.pnas.org/content/early/2018/10/09/1722477115.) In other recent studies it has been reported that while conspicuous insect pest species may be on the rise, the "normal" background insect diversity is shrinking.

In summary, as you continue to record your observations, think about how the seasonal appearances - or sudden rarity- of regionally characteristic species of these rather amusing insects may create a record of a thriving - or declining - natural environment.