2.3. Aphid Performance Bioassay

Several life history parameters, including survival rate, pre-reproductive period, fecundity, and adult weight were evaluated to determine the effects of pre-infestation on performance of subsequent aphids on the pre-infested and control shoots. To determine survival, seven newly emerged nymphs were introduced to each shoot and survival was recorded daily until the last nymph molting (six days). Survival rate (%) was calculated as the number of survived aphids divided by the number of total introduced aphids. After survival determination, the number of aphids on each shoot was adjusted to two to assess fecundity. Aphids were checked every 12 h to record the pre-reproductive period (days), and then every 24 h to record cumulative number of nymphs produced until adult aphids were 14 days old (early fecundity). Nymphs were removed daily to prevent populations increasing and facilitate counting. For the adult weight determination, six newly emerged nymphs were transferred to each pre-treated shoot. After 8 days, when aphids entered adult stage, their weights (mg) were measured individually with a microbalance (precision 0.1 mg). Aphid responses were measured from 15 shoots per treatment for each aphid species, and average data from one shoot was considered as a replicate.