Abstract
The solenopsis mealybug, Phenacoccus solenopsis, has been recently recognized as an aggressively invasive pest in China, and is now becoming a serious threat to the cotton industry in the country. Thus, it is necessary to investigate the molecular mechanisms employed by cotton for defending against P. solenopsis before the pest populations reach epidemic levels. Here, we examined the effects of exogenous jasmonic acid (JA), salicylic acid (SA), and herbivory treatments on feeding behavior and on development of female P. solenopsis. Further, we compared the volatile emissions of cotton plants upon JA, SA, and herbivory treatments, as well as the time-related changes in gossypol production and defense-related genes. Female adult P. solenopsis were repelled by leaves from JA-treated plant, but were not repelled by leaves from SA-treated plants. In contrast, females were attracted by leaves from plants pre-infested by P. solenopsis. The diverse feeding responses by P. solenopsis were due to the difference in volatile emission of plants from different treatments. Furthermore, we show that JA-treated plants slowed P. solenopsis development, but plants pre-infested by P. solenopsis accelerated its development. We also show that P. solenopsis feeding inhibited the JA-regulated gossypol production, and prevented the induction of JA-related genes. We conclude that P. solenopsis is able to prevent the activation of JA-dependent defenses associated with basal resistance to mealybugs.
Highlights
The solenopsis mealybug, Phenacoccus solenopsis Tinsley (Hemiptera: Pseudococcidae), was described originally from U.S.A in 1898 [1], suggesting it is native there
Feeding choice of mealybugs When P. solenopsis adults were offered a choice between leaves from jasmonic acid (JA)-treated and control plants, more adults chose for the leaves from control plants than for the leaves from JA-treated plants, regardless of JA dose (1 mM, G = 11.0, P,0.001; 0.1 mM, G = 7.1, P = 0.008; 0.01 mM, G = 4.7, P = 0.03; Figure 1A)
When P. solenopsis adults were offered a choice between leaves from SAtreated and control plants, the number of adults choosing leaves from control plants did not differ from those choosing for leaves from salicylic acid (SA)-treated plants, regardless of SA dose
Summary
The solenopsis mealybug, Phenacoccus solenopsis Tinsley (Hemiptera: Pseudococcidae), was described originally from U.S.A in 1898 [1], suggesting it is native there. This exotic insect pest has been spreading through out the entire American region since it was first reported in Mexico in 1978. P. solenopsis has been reported to severely affect the cotton industry in Pakistan and India. If P. solenopsis cannot be controlled in all these areas, Wang et al [12] forecasted that the losses in cotton yield in 2008/2009 would be 1.4 million tons in China, 1.12 million tons in India and 0.48 million tons in Pakistan. A basic understanding of the mechanisms of cotton resistance to the mealybugs will provide a new insight into how the eruption of mealybugs occurred and how to develop more durable resistance
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