Pachycondyla obscuricornis as natural enemy of the spittlebug Deois flavopicta

Pachycondyla obscuricornis como inimigo natural da cigarrinha-das-pastagens Deois flavopicta

NOTAS CIENTÍFICAS

Pachycondyla obscuricornis as natural enemy of the spittlebug Deois flavopicta

Pachycondyla obscuricornis como inimigo natural da cigarrinha-das-pastagens Deois flavopicta

Edison Ryoiti Sujii^I; Maria Alice Garcia^II; Eliana Maria Gouveia Fontes^I; Robert James O'Neil^III

^IEmbrapa Recursos Genéticos e Biotecnologia, Caixa Postal 02.372, CEP 70849-970 Brasília, DF, Brazil. E-mail: [e-mail], [e-mail]

^IIUniversidade Estadual de Campinas, Dep. de Zoologia, Caixa Postal 6109, CEP 13083-970 Campinas, SP, Brazil. E-mail: [e-mail]

^IIIPurdue University, Dep. of Entomology, West Lafayette, 47 907-1158 IN, USA. E-mail: [e-mail]

ABSTRACT

The objective of this work was to evaluate the potential control of the ant Pachycondyla obscuricornis Emery (Hymenoptera Formicidae) on populations of nymphs of the spittlebug, Deois flavopicta Stal (Hemiptera Cercopidae). Foraging behavior and prey consumption rate of P. obscuricornis were evaluated. Field data revealed that P. obscuricornis does not show aggressive behavior against individuals of the same species, when they are not carrying a prey; they can patrol distances larger than 10 m searching for prey, and they can build their nest as close as 1 m from each other. The ant has a solitary patrolling habit, there is no recruitment behavior, and individuals dislocate fast, browsing on soil and vegetation for prey. Predation rate on spittlebug nymphs increased relative to the spittlebug abundance, reaching 93.8% of captured prey. Pachycondyla obscuricornis is a voracious predator and may control the population of spittlebugs in cultivated pastures.

Index terms: Insecta, biological control, foraging behavior, predation.

RESUMO

O objetivo deste trabalho foi avaliar se a formiga Pachycondyla obscuricornis Emery (Hymenoptera Formicidae) pode atuar no controle biológico de populações de ninfas da cigarrinha-das-pastagens, Deois flavopicta Stal (Hemiptera Cercopidae). Foram estudados o comportamento de caça da formiga e sua taxa de consumo da presa. Pachycondyla obscuricornis não apresenta comportamento agressivo em relação a indivíduos da mesma espécie, quando estes não carregam presas; pode deslocar-se por distâncias superiores a 10 m em busca de presas e pode nidificar a até 1 m de ninhos da mesma espécie. A formiga apresentou hábito de caça solitário, ausência de recrutamento, e deslocamento rápido pela vegetação. A taxa de predação aumentou com a abundância da cigarrinha, chegando a representar 93,8% das presas capturadas. Pachycondyla obscuricornis é predadora voraz e representa potencial agente de controle de populações da cigarrinha-das-pastagens em pastagens cultivadas.

Termos para indexação: Insecta, controle biológico, comportamento de forrageamento, predação.

Spittlebugs (Hemiptera Cercopidae) are the main pest in cultivated pastures of Central Brazil due to their frequent outbreaks and wide distribution (Valério & Koller, 1992). Production of spittle protects the nymphs against natural enemies and desiccation and, besides the high capacity of colonizing introduced grasses, represents another trait that increases spittlebug's survivor and fitness, facilitating its population growth and damage to pastures (Valério & Koller, 1992; Pires et al., 2000).

Previous studies showed that unspecific predators and parasitoids cause mortality to eggs and nymphs of Deois flavopicta Stal (Hemiptera Cercopidae), reducing their population (Sujii et al., 2002). Various species of arthropods, nematodes and birds have been reported as spittlebug's natural enemies (Carneiro, 1984; Batista Filho, 1988), including few parasitoid insects, such as the egg parasitoid Anagrus sp. which attacks 2% of the eggs (Pires et al., 1993), and predators, such as ants (Hymenoptera Formicidae) (Hewitt & Nilakhe, 1986) and the fly species Salpingogaster nigra Schiner (Diptera Syrphidae) (Marques, 1988).

Surveys in pastures have shown that ants are the most abundant predators and a potentially important biological control agent of spittlebug populations. Individuals of Pachycondyla, Camponotus, Ectatoma, Pheidole, Labidus and Mycocepurus were observed in pastures carrying spittlebug nymphs, and Pachycondylaobscuricornis outstands as the most frequent (Sujii et al., 2002).

The objective of this work was to determine if the ant Pachycondyla obscuricornis has potential to control spittlebug nymph populations.

Methods used focused on P. obscuricornis foraging behavior and prey consumption rate. The foraging behavior of P. obscuricornis was observed by following individuals leaving the nests, attacking prey and carrying them back to the nests, at different periods of the day. At least 40 individuals were observed, 20 in the morning and 20 in the afternoon, to confirm the behavior patterns. To further explore the potential of this species for the spittlebug's population control, this study focused on its patrolling behavior, how it locates and captures the spittlebug nymphs, and its response when encountering other ants.

To evaluate the distribution of P. obscuricornis in a pasture of Brachiaria ruziziensis, a 30x30 m grid was set, with sardine baits placed in Petri dishes 5x5 m apart. Ants foraging at the baits were followed to locate their nests. Some individuals were collected to confirm identification.

A study to evaluate the importance of D. flavopicta in the diet of P. obscuricornis was carried out by observing ants arriving at two nests during a period of intense activity (9–12 AM) on January 16 and 30. Each prey carried to the nest was taken from ants and identified. The densities and instars distribution of D. flavopicta in the field for the same day was estimated by sampling 10 randomly selected quadrats of 0.25 m² in the pasture. To determine occurrence of preference for prey instars, all nymphs were counted, had their developmental stage determined, and had their frequency distribution compared to the frequency distribution of nymphs observed being carried by the ants to the nests´ entrances. The frequency distribution of spittlebug nymphs present in the area and captured by the ants was compared by a Kolmogorov-Smirnov test for the two samples (Wilkinson, 1990).

During the study, D. flavopicta was the main item found in P. obscuricornis diet. The ant was particularly successful in finding nymphs and attacking them inside the spittle. This ant, 12 mm long and displaying a black coloring, has a patrolling habit; individuals hunt and quickly catch all individuals observed. This species shows a solitary foraging behavior; there is no recruitment of other ants for catching or carrying the prey. The Pachycondyla genus has several species specialized in preying on termites (Holldobler & Wilson, 1990). Although there is no reference of P. obscuricornis predating termites, these insects could be the preferred prey attacked in the absence of spittlebugs. Longino (2003) reports P. obscuricornis hunting and carrying caterpillars, in Costa Rica.

P. obscuricornis does not show territorial behavior, but may aggressively dispute prey. Antagonistic or fighting behavior in defense of territories was not observed between individuals from different nests encountering each other (12 observations). The proximity of nests, which can be separated by distances shorter than 1 m (Figure 1), reinforces the absence of territorial aggressive behavior in P. obscuricornis, a trait that can be useful for a biological control agent. Aggressive behavior may occur however, if one of the ants is carrying a prey. In this case, the encounter usually resulted in fight for the prey (three observations). Therefore, even though individuals seem not to frequently compete by interference with each other, competition for food may occur in this system, and is more related to food exploitation, with individuals trying to attack and carry more of the same prey item to their nests.

Observation at the entrance of P. obscuricornis nests showed that the amount of D. flavopicta in ant's diet rose from 63.6% to 93.7% when prey density increased from 40 nynphs/m², at the beginning of the infestation, to 55 ninphs/m² (2^nd–5^th) (Figure 2). The number of nymphs removed by the ants varied from 14 to 61 nymphs, in a three-hour-period (9–12 AM). The frequency of capture was positively correlated with the relative abundance of D. flavopicta and the distribution of prey instars captured was positively correlated with the distribution of instars available in the field. Kolmogorov-Smirnov test on January 16 (MD = 0.75, p=0.13) and January 30 (MD = 0.50, p =0.5) showed that there is no preference for a specific stage or size of spittlebug nymphs, although relative contributions to the diet changed as spittlebug nymphs´ size and abundance increased.

Even though P. obscuricornis patrols distances greater than 10 m from the nest (Figure 1), field observations of presence of nymphs next to the nests (<1 m) suggest that the stimulus for attack is generated by visual perception of nymph movement inside the spittle, and not by the encounter with the spittle itself. This may allow the ant to save time by not searching empty spittle.

From the observations in this study, it can be inferred that, although D. flavopicta is the main component of the P. obscuricornis diet during some periods of the year, and although ants actively search for nymphs in the field, the presence of remaining nymphs of spittlebugs close to the nests indicates the need of further studies to evaluate the control level imposed by P. obscuricornis ants on the spittlebug population.

Acknowledgements

To João Sávio O. Paes, Cristiane Avelar, Shirley Silva, and Andrea Serafini for help surveys and experiments; to Jacques Delabie for the identification of the ant; to Peter Inglis for revision and comments; to Embrapa and CNPq for financial support (141.803/95-9).

Received on November 11, 2003 and accepted on March 19, 2004

• BATISTA FILHO, A. Cigarrinha das pastagens. In CRUZ, B.P.B. (Ed.). Pragas das culturas e controle biológico Campinas Fundação Cargil, 1988. p.78-87.
• CARNEIRO, M.F. Ocorrência de nematóides parasitando ninfas de Deois flavopicta no Município de Goiânia, Goiás Goiânia Emgopa, 1984. 5p. (Pesquisa em Andamento, 9).
• HEWITT, G.B.; NILAKHE, S.S. Environmental factors affeting the survival of eggs and early instar nymphs of spittlebugs Zulia entreriana and Deois flavopicta during the rainy season in central Brazil. Anais da Sociedade Entomológica do Brasil, v.15, p.61-76, 1986.
• HOLLDOBLER, B.; WILSON, E.O. The ants Cambridge Harvard University Press, 1990. 733p.
• LONGINO, J.T. Ants of Costa RicaAvailable in < http //www. evergreen.edu/ants/genera/ Pachycondyla/SPECIES/obsc.../obscuricornis.htm>. Acessed in Oct. 25, 2003.
• MARQUES, I.M.R. Distribuição de Salpingogaster nigra Schiner, 1868 (Diptera Syrphidae) predador específico de ninfas de cigarrinhas da raiz (Homoptera Cercopidae) em algumas regiões do Brasil. Anais da Sociedade Entomológica do Brasil, v.17, p.67-74, 1988. Suplemento.
• PIRES, C.S.S.; FONTES, E.M.G.; SUJII, E.R.; FERNANDES, H.M.C.; GOMES, D.F. Ocorrência de Anagrus sp. (Homoptera Mymaridae) parasitando ovos de Deois flavopicta (Homoptera Cercopidae) em pastagens do Brasil Central. Anais da Sociedade Entomológica do Brasil, v.22, p.411-413, 1993.
• PIRES, C.S.S.; PRICE, P.; SUJII, E.R.; AVELAR, C.S. Feeding behavior of the spittlebug Deois flavopicta (Homoptera Cercopidae) on wild and cultivated host species. Anais da Sociedade Entomológica do Brasil, v.29, p.750-757, 2000.
• SUJII, E.R.; GARCIA, M.A.; FONTES, E.M.G.; O'NEIL, R.J. Predation as a mortality factor in populations of the spittlebug, Deois flavopicta Stal (Homoptera Cercopidae). Neotropical Entomology, v.31, p.581-588, 2002.
• VALÉRIO, J.R.; KOLLER, W.W. Proposição para o manejo integrado das cigarrinhas-das-pastagens. Campo Grande Embrapa-CNPGC, 1992. 37p. (Embrapa-CNPGC. Documentos, 52).
• WILKINSON, L. SYSTAT the system for statistics. Evanson SYSTAT, 1990. 676p.

Publication Dates

• Publication in this collection
  03 Aug 2004
• Date of issue
  June 2004

History

• Accepted
  19 Mar 2004
• Received
  11 Nov 2003