Although ants can be beneficial by suppressing various pests when they are active only on orchard floors, they are generally a problem when they move upwards into citrus trees (Bownes et al., 2014).
Ants intentionally and directly visit Hemipteran insect pests such as soft scales, aphids, whiteflies and mealybugs because of the honey-dew they produce (Samways et at, 1998; Bedford, 1968; Buckley, 1987: Bartlett, 1961; Itioka & Inoue, 1996; Samways et at, 1982).
According to Samways et al. (1982), of the 123 ant species that have been recorded in citrus orchards in South Africa to date, only 44 foraged in trees and only 25 attended to honeydew-producing insects. However, only four species have attained pest status and are listed in order of importance:
- the pugnacious ant, Anoplolepsis custodiens Smith (Hymenoptera: Formicinae),
- the brown house ant, Pheidole megacephale Fabricius,
- the black pugnacious ant, A. steingroeveri Forel, and
- the Argentine ant, Linepithema humile Mayr.
Ant attendance on honeydew-producing hemipteran insect pests is mainly to harvest honeydew, thus protecting the host against parasitoids, predators and even some entomopathogenic fungi.
Observations record that ants assist with the transport of insects and parental care of some hemipteran species to enhance brood production, so confirming their mutualistic, symbiotic relationship.
Red scale does not produce honeydew and it is not, therefore, directly attended by ants. However, increased ant activity disrupts the parasitoids and predators of red scale, and it has been established that certain ant species cause coincident infestations of red scale, among other non-honeydew producing insect pests (Rosen & DeBach, 1979; DeBach et al., 1951; Steyn, 1954b; Compere, 1961; Annecke, 1958; Bedford, 1968; Steyn, 1954a; Pekas et al., 2011; Samways et al., 1982; Samways, 1983; Samways et al., 1998; Flanders, 1945).
It has also been demonstrated that ants compete with parasitoids, including Aphytis spp., for honeydew as a source of carbohydrates produced by non-Aphytis hosts (Calabuig et al., 2015; Tena et al., 2013) and also prey on Aphytis wasps (Heimpel et al., 1997). The constant dis- ruption and interference of host examination and oviposition lead to dramatically reduced efficacy in host parasitism (Rosen & DeBach, 1979; Martinez-Ferrer et al., 2003).
Pugnacious ants tending to a citrus mealybug.
Valencia trees treated with special ant-limiting bands had significantly lower ant (P. megaceph- ala) and red scale infestations than untreated trees (Steyn, 1954a). Similar observations were made by Itioka and Inoue (1996), where the infestation by mealybug (Pseudococcus citriculus Green) in a Satsuma orchard decreased by 94% when the attendant ants (Lasius niger Linnae- us) were excluded. Moreno et al. (1987) found that in the absence of ants, populations of honeydew-producing citrus mealybug (Plano- coccus citri Risso), woolly whitefly (Aleurothrixus floccosus Maskell) and non-honeydew-produc- ing red scale were effectively reduced by their respective natural enemies.
Even in the absence of honeydew-producing scale, the reduction of parasitism of armoured scale by Aphytis spp. due to ant disturbance can be significant, and the effect of ants on Aphytis is rated next to weather extremes and detrimental pesticides (Heimpel et al., 1997; DeBach, Fleschner, et al., 1951; Rosen & DeBach, 1979). Consequently, control of ants is recommended in order to facilitate the biological control of red scale (Rosen & DeBach, 1979; DeBach, Dietrick, et al., 1951; Buckley, 1987; Bartlett, 1961).
Antlions (family Myrmeleontidae) trap ants on orchard floors and are an effective natural enemy of ants when present.
Brown house ants tending to cottony cushion scales.
Pugnacious ants tending to soft brown scales on a new growth flush.
References:
1. Annecke, D.P. 1958. Citrus Grower. Ants and citrus: 1–3.
2. Bartlett, B.R. 1961. The influence of ants upon parasites, predators and scale insects. Annals of the Entomological Society of America, 54: 543–551.
3. Bedford, E.C.G. 1968. The biological control of red scale, Aonidiella aurantii (Mask.), on citrus in South Africa.
Journal of the Entomological Society of Southern Africa, 31(1): 1–15.
4. Bownes, A., Moore, S.D. & Villet, M.H. 2014. My enemy’s enemies: Recruiting hemipteran-tending generalist ants for biological control in citrus orchards by spatial partitioning of foraging webs. African Entomology, 22(3): 519–529.
5. Buckley, R.C. 1987. Interactions involving plants, Homoptera and ants. Annual Review of Ecology and Systematics., (18): 111–135.
6. Calabuig, A., Tena, A., Wäckers, F.L., Fernández-Arrojo, L., Plou, F.J., Garcia-Marí, F. & Pekas, A. 2015. Ants impact the energy reserves of natural enemies through the shared honeydew exploitation. Ecological Entomology, 40(6): 687–695.
7. Compere, H. 1961. The red scale and its insect enemies. Hilgardia, 31(7): 173–278.
8. DeBach, P., Dietrick, E.J. & Fleschner, C.A. 1951. Ants and citrus pests. Calif. Agric., 5(7): 7,14.
9. DeBach, P., Fleschner, C.A. & Dietrick, E.J. 1951. A biological check method for evaluating the effectiveness of
entomophagous insects. Journal of Economic Entomology, 44(5): 763–766.
10. Flanders, S.E. 1945. Coincident infestations of Aonidiella citrina and Coccus hesperidum, a result of ant activity.
Journal of Economic Entomology, 38(6): 712.
11. Heimpel, G.E., Rosenheim, J.A. & Mangel, M. 1997. Predation on adult Aphytis parasitoids in the field.
Oecologia, 110(3): 346–352.
12. Itioka, T. & Inoue, T. 1996. The role of predators and attendant ants in the regulation and persistence of a population of the citrus mealybug Pseudococcus citricuus in a Satsuma orange orchard. Journal of Applied Entomology and Zooligy, 31: 195–202.
13. Martinez-Ferrer, M.T., Grafton-Cardwell, E. & Shorey, H.H. 2003. Disruption of parasitism of the California red scale (Homoptera: Diaspididae) by three ant species (Hymenoptera: Formicidae).
Biological Control, 26(3): 279–286.
14. Moreno, D.S., Haney, P.B. & Luck, R.F. 1987. Chlorpyrifos and diazinon as barriers to Argentine ant (Hymenoptera: Formicidae) foraging on citrus trees. Journal of Economic Entomology, 80(1): 208–214.
15. Pekas, A., Tena, A., Aguilar, A. & Garcia-Marí, F. 2011. The impact of canopy foraging ants on California red scale Aonidiella aurantii in a Mediterranean citrus orchard. IOBC-WPRS Bull., 62(July 2014): 113–117.
16. Rosen, D. & DeBach, P. 1979. Species of Aphytis of the world (Hymenoptera: Aphelinidae). First. David Rosen & Paul DeBach, eds. London: Dr. W. Junk BV Publishers.
17. Samways, M.J. 1983. Inter-relationship between an entomogenous fungus and two ant-homopteran (Hymenoptera: Formicidae-Hemiptera: Pseudococcidae & Aphididae) mutualisms on guava trees. Bulletin of Entomological Research, 73(2): 321–331.
18. Samways, M.J., Grout, T.G. & Prins, A.J. 1998. Ants as citrus pests. In Second, ed. Citrus pests in the Republic of South Africa. Nelspruit: Dynamic Ad: 288.
19. 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.
20. Steyn, J.J. 1954a. The effect of the cosmopolitan brown house ant (Pheidole megacephala F.) on citrus red
scale (Aonidiella aurantii Mask.) at Letaba. Journal of Entomological Society of Southern Africa, 17: 252–264.
21. Steyn, J.J. 1954b. The pugnatious ant (Anoplolepsis custodiens Smith) and its relation to the control of citrus at Letaba. First. J. J. Steyn, ed. Pretoria: The Society.
22. Tena, A., Pekas, A., Wäckers, F.L. & Urbaneja, A. 2013. Energy reserves of parasitoids depend on honeydew from non-hosts. Ecological Entomology, 38(3): 278–289.
More articles by Dr. Ernst de Beer
The definitive field guide
The Laeveld SCOUT™ manuals, a must-have for anybody in the agricultural industry, are authored by Dr. Ernst de Beer, Dr. Jeanne de Waal and Annemarie Bekker.
