136 BR. J. ENT. NAT. HIST., 6: 1993 



elytra and that many tended colonies may not be so well defended, it may be worthwhile 

 for the ladybird to stay and assess the situation and decide whether to remain still 

 and hope to continue feeding or to flee. Wichmann (1955) suggested that Coccinellidae 

 are adapted to attacking ant-tended colonies by keeping still when molested. It is 

 also interesting to note that different species appear to be treated differently by the 

 ants, some being attacked more violently than others. Our observations suggest a 

 number of differences in the interactions between M. ruginodis and different ladybird 

 species. These should be investigated further. 



The ant response results show an increased level of ant hostility after the ladybird 

 has been found on the colony and for about 2 minutes after it has left the colony. 

 This result was suported by observational evidence; for example, on the colony tended 

 by L. niger, after the ladybird had been found on the plant, the ants would sometimes 

 all leave the colony to search for the ladybird, for several minutes. This was the only 

 time we saw the colony untended during the day. 



There could be a number of explanations for these observations; a pheromonal 

 messenger, causing the increase in hostility, could be released either by the ants which 

 encounter the ladybird or by the aphids themselves. This could either be released into 

 the air, in which case it might take several minutes for levels to fall below a threshold 

 value sufficient to stimulate the ants; or it could be released directly onto the ladybird, 

 in which case the formic acid used by the ants is a possible candidate. The latter 

 should seem less likely as the effect seems to be a more general increase in ant activity 

 rather than a specific increase in hostility to the ladybird. This needs to be tested 

 experimentally. 



Acknowledgements 



We are indebted to Mr John Bebbington, the Field Studies Council and the 

 staff at Juniper Hall Field Studies Centre for their help and the use of their 

 facilities. We also thank Maureen Blake and Joanne Griffiths for their typographical 

 services. 



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