This document discusses sequential sampling methods for determining when to take action based on pest counts reaching a threshold. It explains that taking multiple small samples over time and tracking the cumulative count allows making a decision sooner than calculating a single average count from a large sample. Graphs are shown plotting cumulative insect counts against number of plants sampled, with zones for deciding to take action, continue sampling, or take no action. The document also describes using a binomial sampling method of simply counting the number of plants with any pests rather than exact counts.

1. Sequential sampling
How to decide when to ‘take
action’ based on a threshold and
counts
Based on: Robson, J.D., Wright, M.G. & Almeida, R.P.P.
2006. Within-plant spatial distribution and binomial
sampling of Pentalonia nigronervosa Coquerel
(Hemiptera: Aphididae) on banana in Hawai'i. Journal of
Economic Entomology 99: 2185-2190. (Funded by
PBARC, WSARE, TSTAR)

2. The ‘average’
• The average count always has ‘error’ –
counts may range say from 3 to 9, with an
average of 6; or 7; or 5. When can you be
sure you have the correct average?
• Sample size calculations – include error
judgments

3. Sequential sampling
• Have an economic threshold – number of
insect that cause you to take action;
• Take a series of small samples
• Add up numbers of insects
• Make quick decision at low or high pest
density

4. No. plants sampled
15 20 25 30 35 40 45 50
Cummulative
No.
Insects
0
100
200
300
400
500
Continue sampling
Take action
Take no action

5. Sample 15 plants, count insects

6. No. plants sampled
15 20 25 30 35 40 45 50
Cummulative
No.
Insects
0
100
200
300
400
500
Continue sampling
Take action
Take no action

7. Sample 5 more, add number of insect to first 15

8. No. plants sampled
15 20 25 30 35 40 45 50
Cummulative
No.
Insects
0
100
200
300
400
500
Continue sampling
Take action
Take no action

9. Sample 5 more, add number of insects to first 25

10. No. plants sampled
15 20 25 30 35 40 45 50
Cummulative
No.
Insects
0
100
200
300
400
500
Continue sampling
Take action
Take no action

11. No. plants sampled
15 20 25 30 35 40 45 50
Cummulative
No.
Insects
0
100
200
300
400
500
Continue sampling
Stop sampling; Take no action
#1
#2 #3
#4
Low numbers?

12. So much counting! Go Binomial
• Just say yes; or no (any aphids or none)
• Count number of plants with aphids, and
plot them on the graph….
• This saves time and effort, and allows a
quick and accurate decision.

13. # Plants sampled
20 40 60 80 100 120
#
Plants
with
any
Aphids
0
2
4
6
8
10
12
14 Stop sampling, take action if count is in this zone
Stop sampling, do nothing if count is in this zone
Keep sampling until
a decision can be made,
if count is in this zone
Upper stop line
Lower stop line
Action threshold
Action Zone!!
Count-more Zone
No-action Zone