Impact of Two Attending Ants, Crematogaster subnuda and Camponotus compressus (Hymenoptera: Formicidae), on the Parasitism of Sugarcane Aphid Melanaphis sacchari (Zehnt.)

The survey of sugarcane fields was conducted every year from July to April (1998-2003) for five years to record the number of different species of ants and their parasitoids associated with aphid M. sacchari in Western Uttar Pradesh. The behaviour of Crematogaster subnuda Mayr. and Camponotus compressus against Paratrechina longicornis (Latr.) and Tapinoma melanocephalum (Fabr.) and parasitoids Lysiphlebia mirzai Shujauddin, and Aphelinus desantesi Hayat was studied in the field. The presence of ants especially Crematogaster subnuda Mayr. and Camponotus compressus and their role on the effectiveness of parasitoids had been established by selecting three plants with healthy aphid populations for parasitoids activity (i) in the presence of Crematogaster subnuda Mayr. (ii) Camponotus compressus and (iii) in the absence of ants. Ten mated females of L. mirzai were released on each plant and after five days 100 aphids were randomly dissected for evaluating % of parasitism in each case and the experiment were repeated three times. The whole experiments were conducted in a screened glasshouse under controlled condition (22 ± 3℃ Tem. 70%-80% R.H.) described by Kennedy and Booth (1954) and El-Ziady (1960). Statistical analyses and significance tests (P <0.05) were performed using STATISTIX, 1998, and the difference among the percentage parasitism of the aphids attended by ants were tested using chi-square test.

The sugarcane aphid M. saccchri is attended by four species of ants, viz. Crematogaster subnuda Mayr., Camponotus compressus, Paratrechina longicornis (Latr.) and Tapinoma melanocephalum (F.). The first two species are found in abundance (66-30%).Throughout, winter Crematogaster subnuda Mayr. is conspicuously in greater number than Camponotus compresus Fabr. With the result that the former does not permit an easy stay of the later in an aphid colony.These two dominant ants do not permit the other two species Paratrechina longicornis (Latr.) and Tapinoma melanecephalum (F.) to develop contact with the aphids so much so that they are chased away on their mere appearance in the vicinity. The ants dislike the parasitoids and markedly decrease their efficiency is supported from the field observations, where % of parasitism of the aphids attended by Crematogaster subnuda Mayr. had been found very low (20%) than unattended as well as the aphids attended by other ants. Similar results were obtained under controlled condition. The aphids in the absence of ants show highest % of parasitism 68.6% (Table I) and the tendency of dispersion might be due to excess of parasitoids activity. These attended by C. compressus got 31% (Table I) parasitism. However, those attended by the Crematogaster subnuda Mayr. are parasitized in the smaller number (26.3%) (Table I).

When Crematogaster subnuda Mayr. is in abundance and predominantly attending the aphids, it may provide heavy protection by building a cover over the rapidly declining populations. Even, at times it is practically impossible to see the aphids under such covers. It had been found that slight disturbance of aphids by foreign invaders or even by artificial means unquiet the attending ants. The members immediately retaliate assuming an aggressive posture by raising their abdomens vertically upwards. The quick and simultaneous alerting of all the members under such circumstances might be due to the release of pheromones by some ants. Similar, behavior has been noticed for an approaching predator or other wasps attracted to the honeydew, although, neither aphids are disturbed nor there is any possibility of simultaneous perception by all of them. However, if an approaching parasitoid or another kind of ant is noticed, it is chased by the single aggressive ant without alerting other members. It indicates that pheromones are only released in the presence of vague stimuli received via host for searching the invaders or concentrating other members to combat with bigger enemies. The disquiet members start a vigorous search for such invaders and if perceived chase and drive them out for quite long distances. Even at times, they directly attack them by their mandibles and may cause fatal injuries.

The parasitoids are also afraid of the ants which are apparent by frequent interruptions in oviposition under the pressure of aggressive ants and they were seen running away from the hosts before completing a succession and generally taking shelter on the reverse side of the leaf. Even sometimes they have left the host after macro contact before stinging though other condition remains quite favorable. On the other hand, under similar conditions, some female parasitoids behave quite differently. They camouflage

themselves among disturbed aphids by sitting quiet, though, frequently overrun or even occasionally palpated by the disquiet ants. Immediately, after normalization of timid aphids, consequently, settling the aggressive ants, they again resume normal oviposition till other conditions remain favorable. It is quite interesting that a female parasitoid even during its course of oviposition if palpated by the ant is not recognized as intruder unless it gets frightened. The conclusions of Banks (1962), Pontin (1960) and Wichmann (1955) that “ants disregarded the parasites; parasites were not noticed,” a possible explanation for this unique behavior of ants against parasitoids is might be chemical mimicry in which chemical cues on the cuticular surface of some wasps prevent them from being recognized and attacked by mutualistic ants (Völkl, 1992; Völkl and Mackauer, 1993).

The present observations confirm the findings of El-Zaidy and Kennedy (1956), El-Ziady (1960), Völkl and Mackauer (1993), Stechmann et al. (1996), Stadler and Dixon (1999) and Kaneko (2003) that (i) the ants dislike even the nonspecific species, (ii) any foreign invader disturbing the normal life of their attended aphids and (iii) may directly attack them causing fatal injuries with their mandibles are new additions. Some studies on interactions between ants and aphid parasitoids have reported opposing results. Where several studies showed that ant attendance enhanced primary parasitism by some species of aphid parasitoids (Völkl, 1992; Völkl and Stechmann, 1998). A possible reason for this parasitoid preference is that ant tending protects the parasitoid’s offspring against hyperparasitoids and predators (Teegelar et al., 2012; Tegelaar, 2015). Furthermore, wasps developing in ant-attended colonies may benefit from reduced predation, since many predators are attacked and repelled from the aphid colony by tending ants (Banks, 1962; Teegelar et al., 2012; Tegelaar, 2015).

The present writers based on field and laboratory studies on the behavior of aforesaid ants conclude that ants dislike any source which disturbs the normal life of their tended aphids and is an important factor controlling the parasitoid effectiveness.

The authors would like to extend their appreciation to the Research Center for Advanced Materials Science (RCAMS), King Khalid University, Abha, KSA. The second author (ZA) extends his gratitude to the Research Center for Advanced Materials Science (RCAMS), King Khalid University for funding through research program (RCAMS)-04/20.

The authors have declared no conflict of interest.