184 Agroecology and Sustainability
applications for early defoliators, dead-hearts and white heads often led to lower
natural enemy populations allowing the secondary pest, rice brown planthopper
(Nilaparvata lugens), to flare up in massive outbreaks (Rombach and Gallagher,
1994). Work by Kenmore et al (1984) and Ooi (1988) clearly showed the second-
ary pest status of brown planthoppers. Although resistant varieties continue to be
released for brown planthopper, the highly migratory sexual populations were
found to have high levels of phenotypic variation and be highly adaptable to new
varieties. Although wrongly proposed to be ‘biotypes’, it was found that any popu-
lation held significant numbers of individuals able to develop on any gene for
resistance (Claridge et al, 1982; Sogawa et al, 1984; Gallagher et al, 1994). Huge
outbreaks have not reoccurred in areas where pesticide use has dropped due either
to changes in policy regulating pesticides in rice or due to educational activities
(Box 9.2).
A few minor pests are predictable problems and therefore should be considered
for preventive action with natural enemies, resistant varieties, or specific sampling
and control. These include black bug (Scotinophara spp.), gall midge (Orseolia
oryzae), and rice hispa (Dicladispa spp.) which are consistently found in certain
regions; thrips (Stenchaetothrips biformis), whereas drought causes leaf-curling that
provides them a habitat; armyworms (Mythimna spp. and Spodotera spp.) in post-
drought areas that are attracted by high levels of mobilized nitrogen in the rice
plant and panicle cutting armyworms cause extreme damage.
Green leafhoppers (Nephotettix spp.) are important vectors of tungro (see
below) but by themselves rarely cause yield loss. White-backed planthoppers (Sog-
atella spp.) are closely related to brown planthoppers in terms of population
Box 9.2 Predators of BPH: hunting spiders
Predators are the most important natural enemies of BPH. Together with parasitoids
and insect pathogens they keep populations of BPH down. An important group of
predators commonly found in rice fields is the spiders. Of particular importance are
hunting spiders, especially Lycosa pseudoannulata. This is often found near the
water level, the same area where BPH feed. A lycosid is known to feed on as many
as 20 BPH per day. Its voracious appetite makes it a very important natural enemy
of BPH. However, there are often questions asked about this predator.
A common one is: What will the spider feed on in the absence of BPH? Like other
spiders, Lycosa and Oxyopes do not depend entirely on BPH for its food. There are
many flies in the field that provide the bulk of the food for spiders. Studies in Indone-
sia have shown the importance of ‘neutrals’ in supporting a large population of pred-
ators in the rice fields. Spiders are found in rice fields before planting and they
survive on these ‘neutrals’. During the dry season, rice field spiders are known to
hide in crevices or in grasses around the field. Like all predators, spiders are very
susceptible to insecticides and so sprays or granular applications into the water will
destroy these beneficial arthropods, thus allowing BPH to multiply to large num-
bers.