Figure 3.

The time pea aphids and cowpea aphids spent in various feeding activities on alfalfa grown under ambient or elevated CO₂ and O₃. (a–g) Various feeding activities of pea aphids, (h–n) Various feeding activities of cowpea aphids. ‘Phloem feeding’ indicates that aphids are injecting watery saliva into the sieve element and ingesting the phloem sap; ‘potential drops’ indicates that aphids briefly puncture cells during plant penetration; ‘nonpenetration’ indicates that stylets are outside the plants; ‘pathway’ indicates that mostly intramural probing activities between mesophyll or parenchyma cells. Values are the means (±SE) of 21 biological replicates. Different lowercase letters indicate significant differences among the CO₂ and O₃ treatments within the same plant developmental stage. Different uppercase letters indicate significant differences between developmental stages within the same CO₂ and O₃ concentrations.