Cricket Virus Leads to Illegal Importation of Foreign Species for Pet Food
By Joe Ballenger
(An earlier version of this article originally appeared at www.JoeBallenger.com.)
I’m trying to to get back into the tarantula breeding hobby, and decided to set up a cricket colony to help me feed the animals for cheap. I’m not thrilled about using crickets, because they’re not the best feeders for reasons I’m about to discuss. Cockroaches are considered to be the best feeders, but are unfortunately very highly allergenic, even the cockroaches in the pet hobby.
Crickets are curious, oblivious, and relatively defenseless. This combination often leads them to either investigate or ignore the hungry animal that eventually makes them their dinner. Healthy crickets aren’t particularly difficult to keep in captivity, and care-sheets are widely available online. Unfortunately, crickets have been difficult to breed in captivity for some time because the stock from the U.S. isn’t healthy due to an ongoing disease outbreak. The cricket industry has responded in a variety of ways, some of which are quite surprising.
Crickets really don’t need a whole lot to breed. The adults need dirt to lay their eggs, a water source, some food, and crumpled up newspapers to hang out in. Unfortunately, a lot of store-bought crickets die soon after purchase, and most of their offspring don’t make it to maturity. This is because there is an ongoing outbreak of a cricket paralysis virus called Acheta domesticus Densovirus (AdDNV), which has paralyzed the cricket industry.
AdDNV is a virus, originally isolated from pet-store crickets, which causes the crickets to become paralyzed. They’re infected when the nymphs feed on feces or corpses of infected individuals. The virus infects the major tissues of the insects, and eventually they become paralyzed and die as adults.
Densoviruses are arthropod-specific viruses, and are also a huge problem for the shrimp industry. In fact, several densoviruses are among the most problematic pathogens for industrial shrimp farming. Densoviruses are extremely resistant to heat and PH extremes, and are extremely virulent, which makes them able to spread quickly in a population of captive insects. Their intrinsic resistance to environmental extremes makes cricket-rearing facilities very difficult to decontaminate. Furthermore, AdDNV can be found in the dust of cricket-rearing facilities and virtually every surface can test positive for AdDNV. As a result, AdDNV is very difficult to control, and most control measures involve discarding the infected individuals and starting over in a new location. This approach can add up to millions of dollars in losses, and has forced some cricket suppliers into bankruptcy.
Cricket-rearing facilities can be surprisingly large, up to 10,000 square meters. They can also contain an immense amount of crickets; some contain more than 50 million crickets. Each facility can ship to hundreds — or thousands — of pet stores across the U.S. Due to the size of the reptile-breeding industry, the cricket-breeding industry is a multimillion dollar business in the U.S.
The industry reaction to the AdDNV outbreak has been interesting. The obvious reaction is to import resistant species, and use those to replace the susceptible Acheta domesticus, and this is exactly what the cricket industry has done. Many of the species which have been imported as potential replacements are extremely hardy species with a wide diet range, which makes them potentially invasive species. Although there are regulations in place to prevent the import of invasive species, there hasn’t been a whole lot of care taken to follow regulations, and this has become a potentially serious issue.
Domestic Versus Imported Crickets
Now, a little bit about cricket biology and why crickets are potentially problematic, environmentally speaking. Acheta domesticus, the common house cricket, is the cricket which is most important in the pet trade. They’ve been kept as pets since at least the 1700s. They are, for all intents and purposes, as domesticated as dogs or cats.
The crickets you hear around your house during the summer are field crickets in the genus Gryllus. These crickets are, for the most part, widespread in terms of habitat, and they can be abundant in many areas. Both Gryllus and Acheta have broad diets, and can eat a wide range of plant and animal products in captivity. Both are also hardy and can withstand a lot of neglect in captivity. Cricket breeders haven’t had luck breeding A. domesticus that are resistant to AdDNV, so replacement seemed to be the best strategy to keep producing food for reptiles. Thus, Gryllus species were particularly attractive alternatives because they’re hardy and resistant to AdDNV.
The characteristics which make Gryllus species widespread in nature — wide diet preference and tolerance of a broad range of environmental conditions — make them attractive candidates to replace Acheta as pet food. Unfortunately, the fact that they’re widespread in nature also means that they’re likely invasive species. Non-native Gryllus species could become invasive if imported into the U.S., and native Gryllus species could become invasive if imported into different areas of the U.S.
So, importing exotic Gryllus species shouldn’t be desirable because of the risk of releasing a potentially invasive species. Unfortunately, this is exactly what happened after the outbreak of AdDNV. As described in a 2012 Zootaxa article, four new species representing two genera were found to be distributed by American cricket suppliers shortly after the outbreak began. Three were from the genus Gryllus, while another was from the genus Gryllodes.
One species, Gryllus bimaculatus, is a European species which is very widespread. Its range covers at least three continents, from Europe to Asia to Africa. It’s the standard cricket sold in European pet stores, and has replaced A. domesticus as a feeder in Europe. Other pet stores started selling a native U.S. species, Gryllus assimilis, as a feeder species. The USDA has approved G. assimilis because it’s native, whereas sale of the non-native G. bimaculatus is illegal.
Another illegal Gryllus species was also found, but this one was unexpected. Although it looked similar to G. assimilis, its song was different than any other Gryllus species. Scientists eventually discovered that this insect — the crazy red cricket — was genetically distinct from native crickets. In fact, it was a species that had never been described before. They were completely new to science, and nothing was known about their biology — except, of course, that they were resistant to AdDNV. They appear to be related to New World crickets — those from North and South America — but all anyone knows about them is that they might be American. The species was named Gryllus locorojo after its common name (locorojo means “crazy red” in Spanish).
I’m not privy to a lot of details about how the cricket industry is regulated, but I suspect that this potentially serious issue won’t be resolved anytime soon. Crickets, due to their generalist and resilient nature, are potential invasives. Crickets can get released in lots of ways, which makes them especially risky. Pet owners release them into the wild on purpose, and some escape during transfer, so it’s very likely that these crickets will end up in the environment one way or another.
Even worse, it appears the USDA has little power to regulate the market. Regulations in California are a lot more lax than the federal regulations. Even if this weren’t the case, the USDA appears to have little power to regulate the market because the agency lacks a cricket taxonomist.
The industry, for their credit, has apparently adopted the less invasive species. Gryllus locorojo had a reputation for being aggressive, whereas the others were a bit more docile. Many cricket farms nowadays advertise their stock as Acheta domesticus, although there’s no way of knowing if that’s true until you order some. Many don’t even advertise their crickets’ identification.
There was also a fourth species which was imported, Gryllodes sigillatus. This species is found largely in tropical climates, but it’s always found around people. It appears to have adapted to human habitations, and lives specifically in the types of environment we create. According to researchers, it’s the best choice for Acheta replacement as it’s resistant to AdDNV and has a narrow habitat tolerance, which means it’s unlikely to become invasive. The USDA also seems to have been issuing permits for the sale and transport of this species.
I wasn’t aware of any of these issues when I started shopping for my own crickets, and I’m glad I found out about this stuff. I got curious, and decided to look at my breeding stock a bit closer. The females were brown, with wings extended past the tip of their abdomens, which means I procured A. domesticus.
So even after all of this, the original A. domesticus are still for sale.
Liu K., F.-X. Jousset, Z. Zadori, J. Szelei, Q. Yu, H. T. Pham, F. Lepine, M. Bergoin & P. Tijssen (2011). The Acheta domesticus Densovirus, Isolated from the European House Cricket, Has Evolved an Expression Strategy Unique among Parvoviruses, Journal of Virology, 85 (19) 10069-10078. DOI: http://dx.doi.org/10.1128/jvi.00625-11
Meng G., P. Plevka, Q. Yu, P. Tijssen & M. G. Rossmann (2013). The Structure and Host Entry of an Invertebrate Parvovirus, Journal of Virology, 87 (23) 12523-12530. DOI: http://dx.doi.org/10.1128/jvi.01822-13
Szelei J., M.S. Goettel, G. Duke, F.-X. Jousset, K.Y. Liu, Z. Zadori, Y. Li, E. Styer, D.G. Boucias & R.G. Kleespies & (2011). Susceptibility of North-American and European crickets to Acheta domesticus densovirus (AdDNV) and associated epizootics, Journal of Invertebrate Pathology, 106 (3) 394-399. DOI: http://dx.doi.org/10.1016/j.jip.2010.12.009
Weissman D., Gray D., Pham H. & Tijssen P. (2012). Billions and billions sold: Pet-feeder crickets (Orthoptera: Gryllidae), commercial cricket farms, an epizootic densovirus, and government regulations make for a potential disaster, Zootaxa, 3504 67-88. http://www.mapress.com/zootaxa/list/2012/3504.html
Joe Ballenger is an entomologist who specializes in molecular biology and has a thing for wasps. By day, he dreams about having the opportunity to work in pest management research. By night, he loves curling up with a good review paper. Follow him on Twitter at @Stylopidae and at @BugQuestions, and follow his blog at www.JoeBallenger.com.