Some exotic varieties of papaya (Carica papaya) were observed to be highly susceptible to mealybug infestations in 2014 in Sierra Leone, but all local cultivars within the same vicinity were not infested by the same pest. All exotic cultivars infested die. Can somebody help explain why?
Just as in the case of cassava in Nigeria, there was a period that we were losing the available [local] varieties to mealybugs until IITA brought new varieties that were resistant to mealybugs. The plant breeders might have considered incorporating factors that will help the hybrids resist mealy bugs, may be some anti feedants, alkaloids etc. In the situation in Sierraleone it is the other way round; the local varieties are resistant because they have qualities inherent in them that offer that advantage and the exotic cultivars lack what local varieties have.
Intriguing question! As Ogbalo states there must be resistance in the local cultivars, but why? Perhaps local cultivars have "harder growth" that makes feeding more difficult or thief less sugar qualities are less attractive. Another thought is that natural enemies are more abundant on locals. I'd Try increasing nitrate vs ammoniac nitrogen and optimizing potassium and calcium nutrition. We've had excellent results with Cryptolaemus beetles indoors. Can't say if they'd work as well outdoors on papayas, but worth trying.
I suggest you conduct a study comparing the local and the exotic cultivars in terms of morphology, biochemistry, physiology and/or ecology. I'm sure that research will provide valuable insights regarding your observation, and you might even yield findings worth publishing.
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