The sting bug species Bagrada hilaris, sometimes known as the painted bug or bagrada bug, arrived in Chile in 2016 and has quickly become a pest crops—but, for the first time, it has also begun to infest homes, as reported this month in the Journal of Medical Entomology. (Photo credit: Eduardo Faúndez, Ph.D.)

By Eduardo Faúndez, Ph.D.

The stink bug species Bagrada hilaris, also known as the painted bug or bagrada bug, is a stink bug that lately had become a pest in several countries. The species—which has been described from India, where it is a pest of Cruciferae plants—has been recorded in Africa and Europe, and lately it arrived to the New World in 2008 when it was found in California. After that, it started to expand its distribution in the U.S., reached México, and more recently traveled so far as to reach Chile in South America.

Eduardo Faúndez, Ph.D.

B. hilaris is actually a pest in all these places, affecting several crops, mostly Brassica oleracea crops. However, it has been recorded feeding on more than 15 families of plants. In fact, it has become one of the most important stink bug pests worldwide and even has its own chapter in the recent book Invasive Stink Bugs and Related Species (Pentatomoidea): Biology, Higher Systematics, Semiochemistry, and Management. In the Chilean case, we found it near an international airport and an international road in 2016, near the Chilean capital, Santiago.

It rapidly started to expand its distribution and affect growers. However, as it was the first time it had been found that far south in South America, a lot of questions arose on if the insect could become established in the country and what impacts it could cause. Shortly after, in 2017, we found extensive invasion to crops and expanded range distribution, and the bugs started to appear near houses. By the second half of the year, an unexpected situation occurred: For the first time, Bagrada hilaris started to invade homes.

In an article published last week in the Journal of Medical Entomology, I report the first cases of extensive invasions of this bug in homes, finding from a very few specimens to near 300 specimens in a single home. Moreover, these invasions started to affect people, as several residents alleged allergic reactions because of the gland secretions of the bugs. But, perhaps most surprising, the first case of an adventitious bite on a human was recorded.

Here I will stop a little bit to talk about adventitious bites. There is a large misconception in general about true bugs’ biting behavior. It is true that bed bugs and several kissing bugs feed on human blood. Many people believe that these are the only true-bug groups that can bite humans. However, it is common that people get bitten by giant water bugs, damsel bugs, assassin bugs, and many others, usually predaceous. But also, leaf-footed bugs, stink bugs, and other plant feeding bugs have also been recorded to bite humans less frequently. All these bites, the ones from predaceous bugs and plant feeding bugs, are called adventitious bites. These bites do not have the intent of feeding but may happen for one of two main reasons: defense (most common when we are manipulating them) and hydration (i.e., obtaining of water or solutes).

In the case of the B. hilaris bite that I recorded, the bite was most probably for hydration purposes, as there was not a defense situation involved. On the other hand, the home invasions seem to be a more tricky thing to explain. Another invasive stink bug, the brown marmorated stink bug (Halyomorpha halys) is well known to be a nuisance because it forms big aggregations to overwinter in homes. In our case with B. hilaris, that is not a very good explanation, as the invasions started in the spring and worsened in the summer. What I found more likely to be an explanation is that the bugs have been extremely successful in the country, and the populations are so big that they are leaving the wild and agricultural areas with almost no food sources; then, they moved to homes likely just searching for something to eat. That hypothesis also may be related with why they may have started to inflict adventitious bites, and the number of cases may increase in the future.

What catches my attention about this situation and why I decided to collect the data to generate this report is that it struck me as a big shift in behavior for Bagrada hilaris when it reached Chile, and, with a world that is currently changing environmentally, this situation may occur in other places. Also, unfortunately, this situation is hard to treat in Chile, as there are several control programs focused on agroecosystems but nothing related to urban environments. Another problem is that, in agroecosystems, the bugs get a dose of chemical control; however, if they run away from these pesticides and take shelter in homes, they may then return to the crops in short order, as their reproduction rate in the country is very rapid.

As a take-home message, it is interesting to witness the explosion of invasive stink bugs like B. hilaris or H. halys. These species have been restricted to their native ranges for a long time, but just in recent years they have started to expand like crazy and affect us in different and somehow unexpected ways. As it is used to be said, don´t let the bed bugs bite; may I say this time, instead, don’t let the painted bugs bite!

Eduardo I. Faúndez, Ph.D., is an entomologist at the Instituto de la Patagonia, University of Magallanes, in Punta Arenas, Chile. His major research areas are systematics of the Heteroptera and medical zoology.