Carmine spider mites (Tetranychus cinnabarinus) and cotton aphids (Aphis gossypii) are both serious pests of cotton, and cause reductions in yields of this key agricultural crop.  In order to gain insights into how plant defense responses induced by one herbivore species affect the behavior and performance of another, we examined how infestation with T. cinnabarinus influences the development of A. gossypii using cotton as a model.  In this study, we measured the activities of several important biochemical markers and secondary metabolites in the leaves of cotton seedlings responding to infestation by T. cinnabarinus. Furthermore, the influences of T. cinnabarinus infestation on the development of A. gossypii in cotton were also examined.  Our data showed that the activities of several key defense enzymes, including phenylalanine ammonia-lyase (PAL), peroxidase (POD), lipoxygenase (LOX), and polyphenol oxidase (PPO), were substantially increased in cotton seedlings responding to spider mite infestation.  Further, the contents of gossypol and condensed tannins, key defensive compounds, were significantly enhanced in leaves of cotton seedlings following T. cinnabarinus infestation.  Moreover, the T. cinnabarinus-induced production of defense enzymes and secondary metabolites was correlated with infestation density.  The developmental periods of A. gossypii on cotton seedling leaves infested with T. cinnabarinus at densities of 10 and 15 individuals cm^–2 were 1.16 and 1.18 times that of control, respectively.  Meanwhile, the mean relative growth rates of A. gossypii on cotton leaves infested with T. cinnabarinus at densities of 8, 10 and 15 individuals cm^–2 were significantly reduced.  Therefore, these data suggested that the developmental periods of A. gossypii were significantly lengthened and the mean relative growth rates were markedly reduced when cotton aphids were reared on plants infested with high densities of spider mites.  This research sheds light on the role that inducible defense responses played in plant-mediated interspecific interactions between T. cinnabarinus and A. gossypii.

The red imported fire ant (Solenopsis invicta) is a global major invasive pest, and has caused significant economic, social and environmental impacts since its invasion to mainland of China in 2004. To date, chemical control has been the most effective measure. However, the long-term use of chemicals would lead to an unexpected rebound. To understand the risks and explore the mechanisms of detoxification or induction to insecticides in S. invicta, the O-demethylase activity and expression of cytochrome P450 genes of workers and queens, and the effects of chlorpyrifos and fipronil exposure in workers were investigated. Biochemical assays showed the O-demethylase activity of cytochrome P450 was significantly higher in workers than in queens (1.66-fold), and was significantly induced in workers exposed to chlorpyrifos and fipronil, reaching a maximum (3.00- and 1.95-fold) at 48 h and then decreasing dramatically compared to controls (exposed to acetone counterpart). The relative expression levels of 12 cytochrome P450 expressed sequence tags (ESTs) in workers were significantly higher than in queens (from 2.3- to 36.4-fold). Multiple cytochrome P450 genes (except 9E4) were co-up-regulated (from 1.5- to 2.86-fold) in workers exposed to fipronil. These results indicated that the increased O-demethylase activity may result from the increased transcription levels of cytochrome P450 related to detoxification of insecticides in S. invicta. It appears that cytochrome P450 plays an important role in enhanced metabolic detoxification of insecticides. At the same time, it also provides the theoretical basis for resistance management and rational usage of insecticides to control S. invicta.

In order to explore the response dynamics of the activities of defense related enzymes in cotton leaves towards the interactive stress of Helicoverpa armigera herbivory and omethoate application, the activities of phenylalanine ammonia-lyase (PAL), lipoxygenase (LOX), and polyphenol oxidase (PPO) were examined from 6 to 126 h after cotton leaves were treated 12 h of H. armigera herbivory, and then sprayed with 800 mg L–1 omethoate. The results showed that the changes in the activities of PAL, LOX and PPO that occured under the interactive stress of H. armigera herbivory and omethoate application reflected the interactive effects of the two stresses on cotton defense. The similarity between the response dynamics of PAL, LOX, and PPO activities in cotton leaves under the interactive stress and that under H. armigera herbivory treatment alone showed that the induction of H. armigera herbivory on the activities of PAL, LOX and PPO in cotton leaves played a leading role in the interactive effects, and the effect of omethoate application played only a minor role. A joint factor analysis was performed according to a method which has been used to analyze the joint toxicity of pesticides; this analysis sought to clarify if there was a synergistic, antagonistic, or additive effect on PAL, LOX, and PPO activity in cotton leaves resulting from the interactive H. armigera herbivory and omethoate treatment. In the interactive effect on the response of PAL activity in cotton leaves, antagonistic effects of the omethoate application towards H. armigera herbivory were observed at 6 and 12 h. Synergistic effects were then observed at 18 and 30 h. Antagonistic effects were observed from 54 to 78 h and synergistic effects were finally observed at 126 h. The correlation between H. armigera herbivory and omethoate application in the interactive effect on cotton defense responses of LOX activity also fluctuated from synergism to antagonism during the time course. In the interactive effect on PPO activity, only antagonism was observed between H. armigera herbivory and omethoate application. In the interactive stress of H. armigera herbivory and omethoate application on cotton defense responses, omethoate affected the defense responses of cotton to H. armigera herbivory by producing antagonistic and synergistic effects. These results will be useful to understand the relationship between host plant and herbivorous pest.

The 7-ethoxycoumarin O-deethylase (ECOD) activities of cytochrome P450s and differential expression of six cytochrome P450 genes induced by the volatiles from both damaged and undamaged maize plants were investigated in the cotton bollworm, Helicoverpa armigera (Hübner). The ECOD activity changed with time of exposure to maize volatiles. At 36 h after cotton bollworm larvae exposure to maize volatiles, the ECOD activities in cotton bollworm damaged and artificially damaged groups were 2.36 and 4.53 times higher than the control group respectively. The relative expression levels of CYP4S1, CYP6B2 and CYP6B7 in the cotton bollworm were significantly increased in artificially damaged plant group, which was 2.93, 5.09 and 10.66 times higher than that in the control group, respectively. The expression levels of CYP6B2, CYP6B6, CYP9A12, and CYP9A14 were much lower in the larvae exposure to volatiles from both healthy and pest damaged maize seedlings than in the control group at 12 h after larvae exposure to maize volatiles. For the cotton bollworm damaged maize group, the expression of CYP4S1 and CYP9A14 increased.

The gene expression and activity of (+)-d-cadinene synthase during cotton development and in response to stress, as well as the spatial and temporal pattern of sesquiterpene biosynthesis, constitute one of chemical defense mechanisms in cotton plants. In order to explore the effects of omethoate on the cotton defense in relation to (+)-d-cadinene synthase and gossypol, effects of omethoate treatments on activity of (+)-d-cadinene synthase and gossypol content in cotton seedlings were investigated. Cotton seedlings treated with 400 mg L-1 omethoate exhibited a significant decrease in the specific activity of (+)-d-cadinene synthase from 12 to 120 h after treating when compared to the untreated control; significantly lower (+)-d-cadinene synthase activity was also observed in cotton seedlings treated with 200 mg L-1 omethoate from 72 to 120 h after treating; but for cotton seedlings treated with 100 mg L-1 omethoate, from 12 to 120 h after treating, no significant changes were observed for activity of (+)-d-cadinene synthase. The gossypol content in cotton seedlings treated with 100, 200 or 400 mg L-1 omethoate for different time periods showed no significant changes compared to that of the control. These results indicated that the activity of (+)-d-cadinene synthase in cotton seedlings in responses to exposure of omethoate at three concentrations for different time periods followed dose- and time-dependent responses to omethoate exposure. With omethoate as a chemical stress factor for cotton seedlings, the cotton defense in relation to the activity of (+)-d-cadinene synthase in cotton seedlings may be affected by omethoate application.