Rw. Behle et al., EFFECTS OF ALKALINE GLUTEN ON THE INSECTICIDAL ACTIVITY OF BACILLUS-THURINGIENSIS, Journal of economic entomology, 90(2), 1997, pp. 354-360
Insecticidal activity of Bacillus thuringiensis subsp. kurstaki Berlin
er decreases rapidly when exposed to field conditions, but degradation
can be minimized by improving the formulation. Solubilized wheat-glut
en, added to sprayable formulations, forms a film upon drying that res
ists wash-off. Because gluten requires a pH >10 to solubilize, we exam
ined the effects of alkaline pH (with and without gluten) on the insec
ticidal activity of B. thuringiensis. Efficacy of various formulations
was measured by the mortality of neonate European corn borer, Ostrini
a nubilalis (Hubner), fed on treated cotton leaves. In solutions with
pH from 5 to 11, B. thuringiensis (13,800 IU/ml) caused greater than 9
0% larval mortality. Mortality declined significantly (P < 0.05) at pH
12, indicting a loss of insecticidal activity. However, adding 1% (wt
:vol) gluten to the formulations provided 2 benefits that retained the
activity of B. thuringiensis. First, formulations of B. thuringiensis
with gluten caused 97% mortality of larvae at pH 13 compared with 68%
mortality for larvae feeding on leaves treated with the same formulat
ion without gluten. Second, the addition of gluten helped to resist wa
sh-off of B. thuringiensis by 5 cm of simulated rain. Response surface
regression analysis indicated that higher concentrations of gluten (u
p to 1.5% wt:vol) and less alkaline formulations (down to pH 10.5) imp
roved resistance to wash-off. These results indicate that residual act
ivity of B. thuringiensis in the presence of rain may be improved by t
he addition of gluten to the spray mixture.