How the Iberian Ant Can Help Control Pests in Olive Groves

Researchers from the National Museum of Natural Sciences of Madrid and the Biological Station of Doñana, both affil­i­ated with the Spanish National Research Council and the University of Granada, have released a joint study into the effec­tive­ness of the Iberian ant, Tapinoma iber­icum, as a means of con­trol­ling olive grove pests such as the olive moth.

The study, pub­lished in the Journal of Applied Entomology, con­cludes that the species is an ideal can­di­date.

Tapinoma niger­ri­mum was pre­vi­ously con­sid­ered a sin­gle ant species harm­ful to European agri­cul­ture. However, a 2017 study deter­mined that the T. niger­ri­mum com­plex com­prises four dis­tinct species that can be iden­ti­fied only by high-res­o­lu­tion numeric mor­phol­ogy-based alpha-tax­on­omy meth­ods. One of these species is the Iberian ant Tapinoma iber­icum.

To cor­rectly iden­tify the species involved in their study, the team sent spec­i­mens from olive orchards and nat­ural habi­tats through­out the sur­vey area to the Senckenberg Museum of Natural History in Görlitz, Germany, to be iden­ti­fied using the numeric mor­phol­ogy-based alpha-tax­on­omy tech­nique.

The results showed that T. niger­ri­mum tends to inhabit more nat­ural ecosys­tems than T. iber­icum, which was found to inhabit olive orchards in the study region.

Far from being detri­men­tal to agri­cul­ture, the study showed that the oppo­site is true for the Iberian species, which feed on the same type of food regard­less of the agri­cul­tural man­age­ment applied in the dif­fer­ent olive orchards.

This is impor­tant because a preda­tor not affected by man­age­ment could be used to enhance local bio­log­i­cal con­trol plan­ning and strate­gies.

“Undoubtedly, this study can help those who work with agri­cul­tural ecosys­tems, such as farm­ers and tech­ni­cians, to apply bio­log­i­cal pest con­trol both in olive cul­ti­va­tion and in other plan­ta­tions,” said Rubén Martínez-Blázquez, a researcher at the Biological Station of Doñana.

To deter­mine the role of Tapinoma iber­icum in Iberian olive orchards, the researchers applied sta­ble iso­tope analy­sis. This novel approach ana­lyzes the quan­tity and ratio of sta­ble iso­topes in the tis­sues of organ­isms.

Stable iso­topes are atoms with the same num­ber of pro­tons but a dif­fer­ent num­ber of neu­trons and are not radioac­tive. Different iso­topes accu­mu­late in liv­ing tis­sue at dif­fer­ent rates accord­ing to envi­ron­men­tal fac­tors.

Analyzing the iso­topes nitro­gen-15 and car­bon-13 makes it pos­si­ble to track energy or mass flow through ecosys­tems and dis­cern com­plex trophic inter­ac­tions within a food web.

This is because car­bon-13 is elim­i­nated through res­pi­ra­tion and nitro­gen-15 through urine excre­tion, allow­ing one to esti­mate both the car­bon sources in an organism’s diet and the posi­tion of said species within a food web.

However, this requires a set of prior data, such as the time needed for iso­topes to accu­mu­late in the tis­sues of the organ­ism in ques­tion and how the iso­topic fin­ger­print changes or is main­tained over time accord­ing to diet.

The research team acquired this base dataset by rear­ing ants within a lab­o­ra­tory set­ting, feed­ing them with one of four diets: a mix­ture of honey and yeast, aphids that con­sume cover crop plants, olive moth lar­vae or the car­niv­o­rous insect Chrysoperla carnea (green lacewing) which is another impor­tant olive moth preda­tor.

The final analy­sis con­cluded that Tapinoma iber­icum read­ily preys upon Prays oleae at crit­i­cal stages in the pest’s life cycle, mak­ing it an inte­gral part of the bio­log­i­cal con­trol of the species.

In addi­tion, includ­ing the green lacewing in the ini­tial lab­o­ra­tory stage allowed the researchers to con­clude that the ants do not assume the role of hyper-preda­tor, con­sum­ing other species ben­e­fi­cial to the nat­ural con­trol of the olive moth.

“Ants are oppor­tunis­tic, and if there are pests, such as the olive moth (Prays oleae), the ants feed on them,” co-author Francisca Ruano said. ​“Having also proven that they do not become hyper-preda­tors, which could be a prob­lem for other species nec­es­sary to main­tain the health of the soil and the olive tree itself, [they are] ideal can­di­dates to act in the con­trol of this type of pest.”

In Andalusia, the world’s largest olive-pro­duc­ing region, the olive moth is one of the most com­mon olive pests.

Prays oleae pro­duces three gen­er­a­tions per year: the phyl­lophagous gen­er­a­tion, which feeds on olive leaves from November to April and over­win­ters in the canopy; the anthophagous gen­er­a­tion, which feeds on flo­ral buds from April to June; and the car­pophagous gen­er­a­tion when lar­vae pen­e­trate the fruit and feed on the stone from June to October.

All three gen­er­a­tions can cause dam­age to olive groves, and the suc­cess or fail­ure of each gen­er­a­tion deter­mines the size of the fol­low­ing gen­er­a­tion.

Throughout the study, the researchers note that bio­di­ver­sity is crit­i­cal to con­trol­ling pest species by nat­ural preda­tors. This is demon­strated by the increased abun­dance of ants in areas with more com­plex semi-nat­ural habi­tats and reduced pes­ti­cide use.

They found, for exam­ple, that ants liv­ing next to and within organic olive orchards tend to move from the nat­ural adja­cent veg­e­ta­tion to the olive trees mainly when the ground cover starts to wither, cor­re­spond­ing with the time that the olive moth lays its eggs on young olive fruits. Predation at this stage can have a marked impact on sub­se­quent gen­er­a­tions.

• Spanish National Research Council
• AntWiki