Insect Control: Biological and Synthetic Agents - Index of

Table 3 Continued
Number Compound
6: The Spinosyns: Chemistry, Biochemistry, Mode of Action, and Resistance 217
Heliothis
virescens,
neonate
(LC50, ppm)
84 A C17-O-DMPipd 4.1 4.5 24.8
85 A C9-O-L-lyxose a 1.01 1.3
86 A C9-O-L-mannose a 0.04
Cypermethrin 0.18
Ethofenprox 0.3
Fenazaquin 1.0
a L-Lyxose is missing the 6-methyl of rhamnose; L-mannose is 6-hydroxy-rhamnose.
DMAA, dimethylaminoacetate; DMAB, dimethylaminobutyrate; DMAP, dimethylaminoproprionate; DMPipd, dimethyl-N-piperidinyl
acetate; NMPipz, N-methylpiperazinyl acetate.
action because it can be much higher than the true
aqueous concentration, due to partitioning into cell
membranes and binding to hemolymph proteins.
For most insecticides, it is not possible to measure
hemolymph aqueous concentration directly, because
of the difficulty of removing cells and proteins from
whole hemolymph without also removing a portion
of the hydrophobic insecticide from the aqueous
phase. This problem can be circumvented by using
an indirect method to estimate the insecticidal concentration,
whereby the insecticide content of nerve
cords isolated from poisoned, symptomatic insects
is determined and compared with the content of
nerve cords incubated with the insecticide in saline
until a steady state has been reached.
In adult male American cockroaches (Periplaneta
americana) poisoned with a threshold dose of spinosyn
A, the nerve cord content was found to be
4.2 pmol. On the other hand, incubation of isolated
Stomoxys
calcitrans,
adult
(LC50, ppm)
Table 4 Physical properties of spinosyns A and D and 21-butenyl spinosyn A
Aphis
gossypii
(LC50, ppm)
Macrosteles
quadrilineatus
(LC50, ppm)
nerve cords with 100 nM spinosyn A in saline gave
a steady-state tissue content of 19.4 pmol. Assuming
passive distribution of spinosyn A between the
nerve cord and the aqueous medium in vivo and
in vitro allows us to calculate by simple proportionality
that a saline concentration of 21 nM
would give the nerve cord content of 4.2 pmol, as
observed at the threshold dose (Salgado et al.,
1998). Thus, it appears that 20 nM spinosyn A in
the hemolymph should have an effect on the target
receptors that is strong enough to cause symptoms
(Table 6).
6.4. Mode of Action of Spinosyns
Tetranychus
urticae
(LC50, ppm)
Property Spinosyn A Spinosyn D 21-Butenyl spinosyn A
Appearance Colorless solid Colorless solid Colorless solid
Empirical formula C41H65NO10 C42H67NO10 C43H67NO10
Molecular weight 731.96 745.98 757.99
Melting point 120 C 170 C 110 C
Solubility (20 C)
Water (distilled) 89.4 ppm 0.495 ppm
Water (pH 5) 290 ppm 28.7 ppm 184 ppm
Methanol 190 000 ppm 2500 ppm
Hexane 4 480 ppm 743 ppm
Acetone 168 000 ppm 10 100 ppm
Vapor pressure (25 C) 3 10 11 kPa 2 10 11 kPa
Octanol/water
Partition coefficient (pH 7.0, log P) 4.01 4.53 4.37
Adapted, in part, from Anonymous, 2001. Spinosad Technical Bulletin. Dow AgroSciences, Indianapolis, IN; Crouse, G.D., Sparks,
T.C., 1998. Naturally derived materials as products and leads for insect control: the spinosyns. Rev. Toxicol. 2, 133–146; and
Thompson, G.D., Dutton, R., Sparks, T.C., 2000. Spinosad: a case study – an example from a natural products discovery
programme. Pest Mgt Sci. 56, 696–702.
Because spinosad causes excitatory neurotoxic symptoms,
a systematic investigation of the symptoms
using neurophysiology was the most direct way
to identify the target site. Although spinosad is