Insect Control: Biological and Synthetic Agents - Index of

162 4: Insect Growth- and Development-Disrupting Insecticides
Trialeurodes vaporariorum (De Cock et al., 1995;
De Cock and Degheele, 1998; Ishaaya, 2001). It has
no ovicidal activity but suppresses embryogenesis
through adults (Table 14).
Although the exact mode of action of the IGR
cyromazine, which is predominantly active against
dipteran larvae, is not known, evidence has been
presented to suggest that its target site for interference
with sclerotization is different from that of
BPUs (Biddington, 1985). In larvae intoxicated
with cyromazine, the cuticle rapidly becomes less
extensible and unable to expand compared with
the cuticle of untreated larvae. The cuticle may
be stiffer because of increased cross-linking between
the various cuticle components, the nature of which
remains unknown. As summarized in Table 14,
cyromazine is an IGR with contact action interfering
with molting and pupation. It has good systemic
activity. When applied to the leaves, it exhibits a
strong translaminar activity, and when applied to
the soil it is taken up by the roots and translocated
acropetally (Hall and Foehse, 1980; Awad and
Mulla, 1984; Reynolds and Blakey, 1989; Viñuela
and Budia, 1994; Tomlin, 2000).
With classical SAR (Hansch-Fujita), the effects of
different substituents on the benzene rings in BPUs
were analyzed for larvicidal activity against Chilo
suppressalis, S. littoralis, and B. mori (Nakagawa
et al., 1987, 1989a, 1989b). For the benzoyl moiety,
the toxicity was higher with a higher total hydrophobicity,
a higher electron withdrawal from the
side chain, and a lower steric bulkiness of orthosubstituents.
In addition, introduction of electronwithdrawing
and hydrophobic substituents at
the para-position of the phenyl (aniline) moiety enhanced
the larvicidal activity, whereas bulkier
groups were unfavorable. Stacking did not occur
between the two aromatic moieties along the urea
moiety (Sotomatsu et al., 1987). To ascertain the
above results, the relative activity of BPUs was
determined by measuring the incorporation of
[ 14 C]-GlcNAc in larval integuments cultured
in vitro (Nakagawa et al., 1989b). There was a
colinear relationship between in vitro activities and
in vivo larvicidal toxicities if the hydrophobic factor(s)
participating in transport were considered
separately. In addition, integuments of the three
Lepidoptera were incubated in conditions with and
without the synergists piperonylbutoxide (PB)
and S,S,S-tributylphosphorotrithioate (DEF). In the
Qualitative Structure–activity Relation (QSAR)
equation measured without synergist, an electronwithdrawing
effect was favorable to the activity, but
an electron-donating group was favorable to the
activity in the presence of PB. These results mean
that electron-withdrawing groups are playing a role
in suppressing the oxidative metabolism. DEF had
no significant effect, suggesting that hydrolytic degradation
of the phenyl moiety was not of significant
consequence as compared to its oxidative degradation.
In summary, the SAR results suggested that
for BPUs the specific larvicidal spectrum is due
to inherent differences in metabolism in addition
to differences in the physiochemical substituent
effects (Nakagawa et al., 1987, 1989a, 1989b;
Sotomatsu et al., 1987).
4.4.4. Spectrum of Activity
Most CSI compounds are very potent against a
variety of different pests with the highest activity
towards lepidopterous insects and whiteflies. The
main commercial applications are in field crops/
agriculture, forestry, horticulture, and in the home
as summarized in Table 14 (Retnakaran and Wright,
1987; Tomlin, 2000; Ishaaya, 2001). Novaluron
acts by ingestion and contact against lepidopterans
(S. littoralis, S. exigua, S. frugiperda, Tuta absoluta
and Helicoverpa armigera), whitefly, B. tabaci, eggs
and larvae, and different stages of the leafminer,
Liriomyza huidobrensis. Bistrifluron is active
against various lepidopteran pests and whiteflies
an apple, Brassica leafy vegetables, tomato, persimmon,
and other fruits (Kim et al., 2000). Hexaflumuron
and the newer noviflumuron are now used in
bait for control of subterranean termites (Sheets
et al., 2000; Karr et al., 2004). As a specialty in the
series of CSIs, fluazuron is the only ixodicide with a
strong activity against cattle ticks (Kim et al., 2000)
(Table 14).
Buprofezin has a persistent larvicidal action
against sucking Homoptera, such as the greenhouse
whitefly, T. vaporariorum, the sweet potato whitefly,
B. tabaci, both of which are important pests of
cotton and vegetables, the brown planthopper,
N. lugens in rice, the citrus scale insects, Aonidiella
aurantii and Sassetia oleae, and some Coleoptera
and Acarina. In contrast, cyromazine is used for
control of dipteran larvae in chicken manure. It is
also used as a foliar spray to control leafminers
(Liriomyza sp.) in vegetables and ornamentals, and
to control flies on animals (Hall and Foehse, 1980;
Williams et al., 1980; Kanno et al., 1981; Reynolds
and Blakey, 1989; Tomlin, 2000) (Table 14).
4.4.5. Ecotoxicology and Mammalian Safety
Overall, CSIs have selective insect toxicities and as
such are considered ‘‘soft insecticides.’’ For diflubenzuron,
the harbinger of all BPUs, its environmental
fate has been extensively investigated and was