Hemiptera plant. Phloem sap, which has a higher concentration of sugars and nitrogen, is under positive pressure unlike the more dilute xylem sap. Most of the Sternorrhyncha and a number of Auchenorrhynchan groups feed on phloem. Phloem feeding is common in the Fulgoromorpha, most Cicadellidae and in the Heteroptera. The Typhlocybine Cicadellids specialize in feeding on non-vascular mesophyll tissue of leaves, which is more nutritious than the leaf epidermis. Most Heteroptera also feed on mesophyll tissue where they are more likely to encounter defensive secondary plant metabolites which often leads to the evolution of host specificity. Obligate xylem feeding is a
Xylosandrus compactus and "Melia azedarach". It is particularly damaging in tree nurseries, killing seedlings and young saplings. A study in Uganda's shaded robusta coffee systems, tree species suppressing "X. compactus" infestation characteristically exuded copious sap regardless of any stress. Therefore, the presence or absence of copious sap exuding from trees upon injury likely differentiates "X. compactus" hosts from non-hosts. In Florida, where "X. compactus" has been introduced, the life cycle is completed in about twenty-eight days. Like other ambrosia beetles, the adult female carries a fungal symbiont, in this case "Fusarium solani". This fungus attacks the xylem tissue of the plant host,