Increased infestation of Asian citrus psyllids on cold treated sour orange seedlings: Its possible relation to biochemical changes in leaves

Cold stressed sour orange (Citrus aurantium L.) seedling attracted significantly more Asian citrus psyllid (ACP) (Diaphorina citri Kuwayama) during 5 and 24 h recovery periods compared to control plants in choice test experiment. Cold stressed plants were held placed at 6±1°C for 6 days and then transferred to a cage at room temperature (28±2°C) for the ACP choice test. During these 5 and 24 h recovery periods, levels of free alpha amino nitrogen increased by 27% in 24 h post treated samples. Levels of ammonia, a known insect attractant, also increased throughout the recovery period, and after the 24 h ammonia emission was 170% higher in the cold stressed plants than in the controls. Higher levels of putrescine and spermidine were found during 24 h recovery period in cold treated plants than controls. On the other hand, spermine levels in the cold treated leaves decreased by 25% in the first 5 h but then increased to the same levels as the controls in 24 h post cold treatment samples. A number of polyphenols known to be insect deterrents decreased in cold stressed plants. For example, chlorogenic acid, rutin, homoorientin, caffeic acid, naranginin and eriodictoyl decreased significantly in the cold treated plants during 5 and 24 h recovery period. In general, cold stress that increased ACP infestation of sour orange leaves also increased the levels of biochemical insect attractants and decreased the levels of insect deterrents.