Insect Control: Biological and Synthetic Agents - Index of

thus inducing effects and symptomology of a molt
event. One of the first effects of bisacylhydrazine
ingestion by susceptible larvae is feeding inhibition
within 3–14 h (Slama, 1995; Smagghe et al., 1996a;
Retnakaran et al., 1997), which prevents further
plant damage. During this time, synthesis of a new
cuticle begins and apolysis of the new cuticle from
the old one takes place. Subsequently, the intoxicated
larvae become moribund, slip their head capsule
(Figures 9 and 10), and, in extreme cases, the hind
gut may be extruded (Figure 11). The new cuticle
is not tanned or sclerotized. One resulting consequence
is that the mouth parts under the slipped
4: Insect Growth- and Development-Disrupting Insecticides 133
Figure 8 Dose-dependent induction of reporter (b-gal) gene in an ecdysone inducible, transformed yeast cell assay system, with
RH-2485 (methoxyfenozide), RH-5849, and the phytoecdysteroid, ponasterone A. While the fold induction achieved with RH-2485 and
RH-5849 correlate with their relative affinities (indicated on the right of the graph) for the ecdysone receptor (CfEcR) used in this
study, the activation achieved by ponasterone does not correlate with its determined binding affinity to ecdysone receptor.
Figure 9 Scanning electron micrographs of control treated (a and c) and tebufenozide intoxicated (b and d) by ingestion (fava
bean leaves dipped in a 10 ppm aqueous solution and 100 ng, respectively) second instar southern armyworm (a and b) and third
instar spruce budworm (c and d) larvae 48 h after intoxication. In both control armyworm and budworm larvae (a and c), well formed
sclerotized cuticle and mouthparts can be seen. In the intoxicated armyworm (b), the larvae is tricked into undergoing a precocious
molt and the slipped head capsule (SHC) can be seen over the mouthparts. The new cuticle (NC) covering the head is soft,
malformed, and unsclerotized. The soft unsclerotized mouthparts of the intoxicated spruce budworm (d) are shown after manually
removing the slipped head capsule. In both cases, tebufenozide intoxicated larvae initiate a molt, slip head capsule, but are unable
to complete a molt, and hence die of starvation, desiccation, and hemorrhage from the malformed unsclerotized new cuticle.
(Adapted and composed from Dhadialla, T.S., Carlson, G.R., Le, D.P., 1998. New insecticides with ecdysteroidal and juvenile
hormone activity. Annu. Rev. Entomol. 43, 545–569; as well as other unpublished electron micrographs.)
head capsule remain soft and mushy, preventing
any crop damage even if the head capsule came
off from mechanical or physical force. The larvae
ultimately die as a result of their inability to complete
a molt, starvation, and desiccation due to
hemorrhage.
The reasons for the lethal precocious molt
effects of bisacylhydrazines have been investigated
at the ultrastructural level in C. fumiferana
(Retnakaran et al., 1997), in beet armyworm,
Spodoptera exigua (Smagghe et al., 1996c), in tomato
looper, Chrysodeixis chalcites (Smagghe et al.,
1997), in the Colorado potato beetle, Leptinotarsa