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Trapping was done using three sticky traps, three pheromone traps, and
a light trap (Table 1).
Insecticide-treated plots were sprayed by the farmer using the same
timing and dosage as on his own adjacent field. Between 24 February
and 25 June, insecticides were applied 18 times; Hostathion (triazophos)
was used most frequently and Dicarzol (formetanate hydrochloride),
Decis (deltamethrin), and Azodrin (monocrotophos) less often.
Untreated plots served as controls.
Eggplants were harvested every 3-4 days and fruit was graded as class A
(large and undamaged), class B (small or slightly damaged), and rejects
(damaged by insects, rot, or discoloration). Weight and market price of each
grade were recorded. After harvest, five plants were selected at random in each
plot and examined for fruit and shoots damaged by Leucinodes, an indirect but
efficient method of assessing larval population. The average number of other
pests and beneficial insects per leaf was also recorded.
Previous studies on Leucinodes, including those using an unsprayed control
plot, have usually taken place in fields where most of the area was sprayed
with insecticides. Such practices do not allow for the establishment of a full
complement of predators and parasites in control fields. In this study, all
unsprayed plots were grouped together, with large border areas, to create the
largest possible block of unsprayed plants: 60 m2 was allocated to each
treatment in the midst of 1 584 m2 of untreated plants. The overall yield of the
experimental field was compared with that of the adjacent farmer's field.
Vegetables grown without pesticides often sell at higher prices in the marketplace
because customers are willing to pay more for the assurance of pesticide-free
food. These premium prices provide an extra incentive for farmers
who are considering nonchemical pest-control methods. To determine
whether local consumers would pay more for unsprayed eggplant, a preliminary
marketing study was conducted at theUniversity of the Philippines at
Los Banos (UPLB).
Results and discussion
Previous work (Navasero 1983) determined that the life cycle of Leucinodes
(egg to egg) in the Philippines was 23-30 days (mean, 25 days). Monitoring
larval damage revealed distinct peaks at 23- to 31-day intervals (mean,
27 days), with minima over the same period occurring on average 16 days
after the peaks, indicating the presence of a nearly synchronous population.
Damage was highest when most of the pest species was present as larvae. The
lows occurred when larvae had left the plants to pupate.
Understanding the life cycle and population dynamics of a pest is crucial for
timing the release of biological control agents that usually attack only one
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