California Pest Rating Proposal for
Difficult White-Footed Ant | Technomyrmex difficilis Forel
Current Pest Rating: Q
Proposed Pest Rating: A
♦ Comment Period: 3/2/18 – 4/16/18 ♦
Technomyrmex difficilis is currently Q-rated. A permanent pest rating proposal is required to support an official pest rating.
History & Status:
Background: Technomyrmex difficilis is a small (2.5-3 mm in length) ant that is mostly dark brown in color with distinctively paler tarsi (Warner et al., 2016). There are other potentially harmful species in the genus that look very similar, and microscopic examination of minute characters is necessary for a specific diagnosis (Wetterer, 2008; Wetterer, 2013). This ant feeds on plant nectar, honeydew (a sugary liquid produced by plant sap-feeding insects), and dead insects or other protein-rich foods (Warner et al., 2016). This and other Technomyrmex species may protect plant-feeding Hemiptera and thus be agricultural pests (Deyrup, 2016; Samways et al., 1982). Technomyrmex difficilis occurs in man-made (urban and residential areas) and natural (e.g., forest) environments and appears to be most abundant in disturbed and coastal areas. Nests can be found in leaf litter, in trees (in tree holes or under bark), and in buildings (in wall cavities or attics) (Wetterer, 2008). This ant often occurs in large numbers, and although it does not bite or sting and it has not been reported to cause structural damage to buildings, it is an annoyance to homeowners (Warner et al., 2016).
Worldwide Distribution: Technomyrmex difficilis is probably native to Madagascar. It has been introduced to Asia (including Indonesia, Malaysia, and the Philippines), Australia, the Caribbean, Central America, and the United States, where it has been reported from Georgia, Hawaii, Louisiana, Missouri, North Carolina, Oklahoma, South Carolina, Washington, Washington D.C., and Florida (Deyrup, 2016; Warner et al., 2016; Wetterer, 2008; Wetterer, 2013).
Official Control: This ant does not appear to be under official control anywhere.
California Distribution: Technomyrmex difficilis is not known to occur in California (Essig Museum of Entomology holdings database; Symbiota Collections of Arthropods Network; Wetterer, 2013).
California Interceptions: Technomyrmex difficilis has been intercepted on fruit (grapefruit and longan) and miscellaneous goods from Florida (PDR # BL0P06126651, 430P06002358, 010P06220447, WHOPO6180098, 010P06220393, 070P06223950, BL0P06612374, NE0P06374846, NE0P06655880, WH0P06181195, 190P06619841, and NE0P06654767), cut flowers and leaves from Hawaii (PDR # 100P06282884, 190P06619904, 410P06325136, 410P06325130, and 100P06282591), and a bee colony from Texas (PDR # VL0P06677067).
The risk Technomyrmex difficilis would pose to California is evaluated below.
Consequences of Introduction:
1) Climate/Host Interaction: Technomyrmex difficilis has become established in many different parts of the world, but (with the exception of greenhouses, zoos, and other artificial environments in temperate areas) it appears to be limited to areas with a tropical or sub-tropical climate. It is possible that it could become established in a larger, but limited part of California. Therefore, Technomyrmex difficilis receives a Medium (2) in this category.
– Low (1) Not likely to establish in California; or likely to establish in very limited areas.
– Medium (2) may be able to establish in a larger but limited part of California.
– High (3) likely to establish a widespread distribution in California.
2) Known Pest Host Range: Technomyrmex difficilis is known to feed on nectar, honeydew, and a variety of protein-rich foods, which could include insects and other animals. Therefore, it receives a High (3) in this category.
– Low (1) has a very limited host range.
– Medium (2) has a moderate host range.
– High (3) has a wide host range.
3) Pest Dispersal Potential: Winged females and males are produced by the colony each year. They fly, copulate, and establish new colonies. Movement of infested landscaping plants may be an important means of artificial dispersal (Warner et al., 2016). Therefore, this ant receives a Medium (2) in this category.
– Low (1) does not have high reproductive or dispersal potential.
– Medium (2) has either high reproductive or dispersal potential.
– High (3) has both high reproduction and dispersal potential.
4) Economic Impact: Technomyrmex difficilis is reported to protect plant sap-feeding insects, including mealybugs, from natural enemies. Another species of Technomyrmex was reported to protect the scale Aonidiella aurantii, which became abundant enough to cause defoliation of citrus trees (Samways et al., 1982). Technomyrmex difficilis could have the same impact in California, and this could lower crop yield and increase production costs. Therefore, it receives a Medium (2) in this category.
Economic Impact: A, B
A. The pest could lower crop yield.
B. The pest could lower crop value (includes increasing crop production costs).
C. The pest could trigger the loss of markets (includes quarantines).
D. The pest could negatively change normal cultural practices.
E. The pest can vector, or is vectored, by another pestiferous organism.
F. The organism is injurious or poisonous to agriculturally important animals.
G. The organism can interfere with the delivery or supply of water for agricultural uses.
Economic Impact Score: 2
– Low (1) causes 0 or 1 of these impacts.
– Medium (2) causes 2 of these impacts.
– High (3) causes 3 or more of these impacts.
5) Environmental Impact: Ants of the genus Technomyrmex have been shown to be capable of having positive and negative impacts on plants. An example of a possible positive impact is feeding on herbivorous insects, thus protecting the plant. An example of a possible negative impact is tending (feeding on honeydew produced by, and protecting from natural enemies) herbivorous insects, such as mealybugs, which would hurt the plant. This suggests that these ants could disrupt natural communities; they could for instance, facilitate the invasion of an ecosystem by an introduced plant through feeding on herbivorous insects (Lach et al., 2010). The species albipes was shown to have “supercolony” characteristics by Dejean et al. (2010); members from widely-separated colonies recognized each other, which could give this species a competitive advantage. Technomyrmex difficilis could behave similarly. Therefore, it receives a Medium (2) in this category.
Evaluate the environmental impact of the pest on California using the criteria below.
Environmental Impact: A
A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.
B. The pest could directly affect threatened or endangered species.
C. The pest could impact threatened or endangered species by disrupting critical habitats.
D. The pest could trigger additional official or private treatment programs.
E. The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.
Score the pest for Environmental Impact. Score:
Environmental Impact Score: 2
– Low (1) causes none of the above to occur.
– Medium (2) causes one of the above to occur.
– High (3) causes two or more of the above to occur.
Consequences of Introduction to California for Technomyrmex difficilis: Medium (11)
Add up the total score and include it here.
–Low = 5-8 points
–Medium = 9-12 points
–High = 13-15 points
6) Post Entry Distribution and Survey Information: Technomyrmex difficilis is not known to occur in California. It receives a Not established (0) in this category.
–Not established (0) Pest never detected in California, or known only from incursions.
–Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).
–Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.
–High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.
7) The final score is the consequences of introduction score minus the post entry distribution and survey information score: Medium (11)
This ant has been confused with the very similar T. albipes. Both T. difficilis and T. albipes have been widely introduced, neither are known to occur in California, and they probably pose a similar economic and environmental threat to the state (Wetterer, 2008; Wetterer, 2013). Because of the confusion between T. difficilis and other Technomyrmex species, the distribution and impact of T. difficilis as it is currently understood may be an underestimate (Wetterer, 2013).
Conclusion and Rating Justification:
Technomyrmex difficilis is not yet known to occur in California. It has demonstrated an ability to become established and abundant in a variety of habitats. It poses a threat to California’s agriculture and environment. For these reasons, an “A” rating is justified.
Dejean, A., Fisher, B.L., Corbara, B., Rarevohitra, R., Randrianaivo, R., Rajemison, B., & Leponce, M. 2010. Spatial distribution of dominant arboreal ants in a Malagasy coastal rainforest: Gaps and presence of an invasive species. PLoS ONE. 5(2): 1-7.
Deyrup, M. 2016. Ants of Florida. CRC Press. 437 pp.
Essig Museum of Entomology holdings database. Accessed February 27, 2018.
Lach, L., Tillberg, C.V., & Suarez, A.V. 2010. Contrasting effects of an invasive ant on a native and an invasive plant. Biological Invasions. 12: 3123-3133.
Samways, M.J., Nel, M., & Prins, A.J. 1982. Ants (Hymenoptera: Formicidae) foraging in citrus trees and attending honeydew-producing Homoptera. Phytophylaciica. 14: 155-157.
Symbiota Collections of Arthropods Network. Accessed February 27, 2018. http://scan1.acis.ufl.edu
Warner, J., Scheffrahn, R.H., & Cabrera, B. 2016. White-footed ant, Technomyrmex difficilis (=albipes) Forel (Insecta: Hymenoptera: Formicidae: Dolichoderinae). Department of Entomology and Nematology, UF/IFAS Extension. https://edis.ifas.ufl.edu/pdffiles/IN/IN55100.pdf
Wetterer, J. K. 2008. Technomyrmex difficilis (Hymenoptera: Formicidae) in the West Indies. Florida Entomologist. 91(3): 428-430.
Wetterer, J.K. 2013. Worldwide spread of the difficult white-footed ant, Technomyrmex difficilis (Hymenoptera: Formicidae). Myrmecological News. 18: 93-97.
Kyle Beucke, 1220 N Street, Room 221, Sacramento, CA, 95814, 916-403-6741, plant.health[@]cdfa.ca.gov
Jason Leathers, 2800 Gateway Oaks, Sacramento CA 95833, (916) 654-1211, plant.health[@]cdfa.ca.gov
3/2/18 – 4/16/18
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