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stage of the life cycle. Trichogramma are most effective if released as the adult
pest begins to lay eggs. For Leucinodes, this occurs, on average, 1 day after
emergence of the adults or 10 days after cocoon spinning (Navasero 1983), i.e.,
when larval population is lowest. Field release can be timed from the last peak
(add 16 days) or the last low (add 27 days).
Euborellia consume the larvae of Leucinodes and must be released during the
11-day larval period. This period is marked by an abrupt increase in crop
damage as eggs hatch and larvae begin boring into shoots and fruit. Euborellia
released at the beginning of this stage are most effective in controlling the pest
species. Fieldwork is continuing to evaluate the level of control attained with
one and two releases of Euborellia per Leucinodes life cycle.
Knowledge of the population fluctuations of Leuci nodes may also prove useful
for control methods not considered in this study. For example, the nematode
Neoplectana carpocapsae may be used against pupal Leucinodes (Janardar and
Bardhan 1974). On the other hand, if chemical methods prove necessary, their
effectiveness can be increased by spraying during the most susceptible stage
of the pest's life cycle.
Over a period of 17 weeks, none of the biological, cultural, or chemical control
methods tested produced higher yields than the untreated plots in the experimental
field (Table 2). However, Leucinodes caused less damage in four treated
plots than in the control plots. Damage was lowest in plots sprayed with
insecticide, followed by those cleared manually, Trichogramma treated, and
Euborellia treated. These results may be due to the late start of biological control
treatments and damage caused by insects other than Leuci nodes, especially
thrips and mites.
The insecticides used against shoot borers do not control thrips and mites;
populations of both these pests increased noticeably in sprayed plots during
the dry season. They caused leaf yellowing, reduced yield, and defoliation. In
unsprayed plots, these symptoms appeared later and were less severe, probably
because the pests were held in check by predators and parasites present
Table 2. Comparison of Leucinodes damage and yield of eggplant
for various treatments.
Treatment Damagea Yield (kg)b
Control 347 111.0
Manual sanitation 263 106.6
Trichogramma 266 105.3
Euborellia 341 98.7
Trapping 395 97.7
Insecticide 169 93.2
a Cumulative number of Leucinodes-dama god fruit and shoots in
90 plants, monitored after every harvest.
b Cumulative yield of three 20-m2 plots.
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