The results show that chemical applications
against leafminers involving Profenofos and
Carbosulfan were ineffective in controlling these
target pests. Moreover, applications of both these
pesticides had deleterious effects on the beneficials,
reducing parasitism. Thus while these chemicals are
widely applied by farmers, their effects appear to be
negative rather than positive. As the same fungicide
treatments were used in the sprayed and control
plots, the effects can be attributed to the insecticides
per se. Pesticides including pyrethroids and organophosphates
are considered ineffective against
L. huidobrensis because of resistance (Macdonald
1991; Weintraub and Horowitz 1995). As Indonesian
populations of L. huidobrensis are likely to havebeen derived from invasions of resistant European
populations, these are also likely to be resistant.
In contrast, the Abamectin treatments were
successful in reducing damage without deleterious
effects on the parasitoids. Abamectin as well as the
insect growth regulator Cyromazine have provided
effective control of L. huidobrensis in several countries
(Vandeveire 1991; Hammad et al. 2000; Weintraub
2001). Abamectin may be harmful to beneficials
including parasitoids (Consoli et al. 1998; Darvas
and Andersen 1999; Shipp et al. 2000). In laboratory
studies, it was shown to kill Indonesian parasitoids
but only at rates above those applied in the field
(Prijono et al. 2004). Adult parasitoids were more
tolerant of Abamectin than the target leafminer
L. huidobrensis, and this chemical was far less toxic
than other compounds used by Indonesian farmers
(Prijono et al. 2004).
Unfortunately Abamectin treatments are relatively
expensive when compared to applications of other
compounds used more widely by farmers. However,
the Abamectin trial shows that numerous applications
of this chemical are unnecessary to obtain
sufficient control. A few applications, to coincide
with the presence of larvae at 40 days after planting,
may suffice, given that damage levels were similar
regardless of whether sprays were applied prior to this
time. The importance of well-timed sprays is also
evident in the results of Weintraub (2001), who