A simple, precise and economic method was developed to evaluate
the residual toxicity of a pesticide to natural enemies. The highest commercial
dose recommended by the manufacturer was sprayed on Petri dishes using
a Potter tower or immersing the dishes in a diluted solution of the pesticide.
The relative toxicity of a pesticide was compared using mean lethal time
(TL
50
's) in 4 categories. The first category comprised the most toxic
responses between 0h< TL
50
< 2h, and included: Azinphosmethyl on
Neoseiulus chilenensis
(Dosse) and
Phytoseiulus persimilis
Athias-Henriot; Chlorfenvinphos on
Amitus spiniferus
(Brèthes),
Lysiphlebus testaceipes
(Cresson),
Pauridia peregrina
Timberlake and
Scutellista caerulea
(Fonscolombe); Chlorpyrifos on
A. spiniferus
,
L. testaceipes
,
Metaphycus flavus
(Howard);
P. peregrina
and
P. persimilis
; Diazinon on
M. flavus
and
P. persimilis
; Esfenvalerate on
P. persimilis
; Formetanate on Orius insidiosus (Say); Imidacloprid on
A. spiniferus
,
L. testaceipes
,
M. flavus
,
P. peregrina
,
S. caerulea
; Methamidophos on
O. insidiosus
; Methomyl on
O. insidiosus
; Permethrin on
N. chilenensis
and
P. persimilis
. The second category consisted of TL
50
's between 2h< TL
50
< 5h and included: Chlorpyrifos on
S. caerulea
. The third category consisted of TL
50
's between 5h< TL
50
< 24h and included: Copper oxychloride on
A. spiniferus
and
L. testaceipes
. The fourth category consisted of TL
50
's after 24h>>TL
50
and included: Copper oxychloride on
S. caerulea
. The results of this study agree with those obtained by other researchers
who used methods accepted by the International Organization for Biological
Control of Noxious Animals and Plants (IOBC), which differ from the methodology
utilized in this study. The results suggest that Lethal Time for 50% mortality
is a quick, precise and economical method to establish the preliminary
toxicity of a pesticide to natural enemies.