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ria, treat with antibiotics." Therefore, we 

 fed our female ladybirds tetracycline in 

 syrup (the best way to get ladybirds to take 

 medicine). 



Our frugal approach paid off. Almost 

 immediately, the hatch rate of eggs laid by 

 the treated females increased, suggesting 

 that males were now surviving. And in- 

 deed, when we examined the offspring 

 produced by these females, we found 

 roughly equal numbers of each gender. 

 Our killer appeared to be a bacterium. Mi- 

 croscopy subsequently corroborated this 



analysis, and further work by Jack Werren, 

 of the University of Rochester, produced 

 molecular confirmation: a bacterium, 

 passed down from mother to daughter, had 

 killed the sons. 



Like any other organism, this bacterium 

 should be trying to reproduce, to perpetu- 

 ate itself. But in killing the males, it ap- 

 pears to be committing suicide. So what 

 does the bacterium have to gain by such 

 misandrous behavior? A great deal, sug- 

 gests ladybird ecology. By killing male 

 embryos early in their development, a bac- 



The typical two-spotted ladybird beetle is 

 a rich red with two black spots. Dark 

 individuals, however, are not uncommon 

 and are as successful as their more 

 traditionally colored conspecifics at 

 finding food and mates. 



Michael Majerus 



33 



