Which life stage is targeted by horticultural oils for oystershell scale?

Which life stage is targeted by horticultural oils for oystershell scale?

• A. Crawlers
• B. Eggs
• C. Adults
• D. Pupae

Answer: (A)

Horticultural oils are most effective when they cover exposed, soft-bodied life stages. For oystershell scale, the crawlers—the first-instar nymphs that have hatched and are moving to feed—are the vulnerable stage. They lack the protective scale cover that adults have and aren’t yet sealed off, so a thorough oil film can smother them and prevent respiration. Eggs are tucked under the female’s scale and aren’t reached well by oil, and adults are largely protected by their hard outer covering, making them much less susceptible. So the crawler stage is the best target for this treatment.

Horticultural oils are most effective when they cover exposed, soft-bodied life stages. For oystershell scale, the crawlers—the first-instar nymphs that have hatched and are moving to feed—are the vulnerable stage. They lack the protective scale cover that adults have and aren’t yet sealed off, so a thorough oil film can smother them and prevent respiration. Eggs are tucked under the female’s scale and aren’t reached well by oil, and adults are largely protected by their hard outer covering, making them much less susceptible. So the crawler stage is the best target for this treatment.