## 4 Discussion
In addition, we detected increases in _allo_-ocimene and \(\beta\)-ocimene in response to pysllid infestation that was \(\sim\)1.5-fold higher than in the control trees. [PERSON]. [66] detected increased levels of these two monoterpenes in HLB-infected citrus and as a result of priming healthy citrus trees with methyl jasmonate, similar to what would occur during an infestation. We also saw significant increases in \(\alpha\)- and \(\beta\)-pinene, thymol, p-cymene, and p-cymen-8-ol in the pysllid-infested trees. These compounds were linvicidal to mosquito larvae and reduced oviposition of females at concentrations of 20 mg\(\cdot\)L\({}^{-1}\)[67]. On the other hand, \(\beta\)-pinene increased the oviposition of female mosquitos and neither \(\alpha\)-pinene nor \(\beta\)-pinene were efficient lavricides without the addition of a cytochrome P\({}_{450}\) inhibitor [67]. These data suggest that the efficacy of the individual compounds may suffer compared to the natural blends of VOCs that are produced by plants. Phenylpropanoids and benzenoids, which arise from phenylalanine via phenylalanine ammonia lyase (PAL) to _trans_-cinnamic acid, make up the second largest class of plant VOCs, playing roles in both pollinator mediation and plant defense, and rootstocks can affect changes in the accumulation of these compounds under different abiotic and biotic stresses [9; 59]. In this study, we detected several phenylpropanoids and benzenoids, including chavicol, coumarin, and ethyl 4-ethoxybenzoate, and these were consistently reduced in the infested Sugar Belle/US-897, but increased on the C-35 and SO rootstocks. Overall, however, phenylpropanoids and benzenoids represented the smallest portion of leaf VOCs (2-6% of total peak area), as they are more typically associated with floral VOCs [59]. In 'Moro' blood orange fruits from C-35 rootstock, the concentrations of chlorogenic, ferulic and sinapic acids were highest among eight rootstocks that were tested by liquid chromatography (HPLC) [26]. The low values that were found in our samples are likely a result of both the tissue type and using GC-MS rather than HPLC, which is more suitable for this class of compounds. For example, in our previous work, Sugar Belle was among the highest of 23 varieties for phenolics and flavonoids content, and Dancy tangerine, one of the parents of Sugar Belle, was highest hydroxycinnamic in acid-related compounds by HPLC methods [68]. Higher levels of these compounds may contribute to the reported tolerance of Sugar Belle toward HLB compared to sweet orange and grapefruit varieties. Among the highest increased fold changes that were found in Sugar Belle that was infested with _D. citri_ were in the fatty acids palmitic acid methyl ester and stearic acid. The roles of fatty acids in plant metabolism are well established and are abundantly present in the leaves, flowers, seeds, and cuticle waves of many species. The nutritive value of fatty acids that are found in forage or silage crops is critical to the diets of many animals [69], and are valued as essential nutrients for humans. In citrus, fatty acids are found primarily in the peel oil glands, leaves, seeds, and juice sacs ([PERSON] & [PERSON], 1971). Gueta-Dahanetal. [70] correlated a 20% increase in palmitic acid (C16:0) and linoleic acid (C18:2) content with abiotic stress (salt stress) in a salt-tolerant cultured citrus cell line, and with an accompanying decrease of 50% in linolenic acid (C18:3) content. The changes in lipid metabolism were mediated constitutively by superoxide dismutase (SOD) in an effort to quench reactive oxygen species [70]. Interestingly, we found the opposite effect in psyllid-infested citrus trees, suggesting that biotic stress may alter citrus lipid metabolism through a different mechanism. The infestation with _D. citri_ initiated a severe decline in the levels of methyl linolenate.