Influences Of Methanol, Formaldehyde, And Formaic Acid On The Cotton Bollworm, Helicoverpa Armigera (Lepidoptera: Noctuidae) And Its Host Maize (Zea Mays L.)

Methanol is produced by and emanated from most plants, especially during early stage of development in nature. In plant, methanol is generally oxidized to formaldehyde and subsequently to formic acid. Methanol, along with its oxidized compounds, formaldehyde and formic acid, may mediate the relationship between herbivore and host plant. Here we studied the affects of methanol and its oxidized compounds on the cotton bollworm, Helicoverpa armigera, and its host plant, Zea mays L.In the laboratory the toxicities of methanol, formaldehyde, formic acid to H. armigera was examined. (1) Methanol and its oxidized compounds can kill neonate and larvae, with the LC50 values to the 3rd instar larvae for methanol, formaldehyde and formic acid being 0.051, 0.081 and 0.033 g per g diet and the LC50 values to the 4th instar larvae being 0.050, 0.083 and 0.041 g per g diet respectively. (2) When the 3rd instar larvae exposed on the artificial diet contained 0.032 g methanol, 0.054 g formaldehyde, or 0.041 g formic acid per g diet for 1 day, the pupal weight was reduced to 0.28, 0.27, 0.26 g respectively from 0.35 g. When exposed on the artificial diet contained 0.054 g formaldehyde per g diet continuously until pupation, the pupal weight was further decreased to 0.19 g.EAG responses of H. armigera mated moths to myristic, palmitic, stearic and olic acids and their corresponding methyl esters were determined. Each of the test chemicals elicited significant EAG responses above solvent and background when applied in an amount of 5μg per filter paper strip. Palmitic acid, methyl myristate and methyl oleate gave higher EAG responses than others. EAG responses to each chemical of male and female moths were compared. EAG values from mated females to palmitic acid and methyl myristate were significantly stronger than values from mated males. In contrast, EAG responses from mated females to stearic acid, oleic acid and methyl oleate were significantly lower than responses from mated males. Morefore, differences of EAG responses of H. armigera mated moths to methyl palmitate and methyl stearate in scotophase and photophase was recorded. These results demonstrated that H. armigera moths may detect the methanol metabolites olfactorily by antennae.The influences of aqueous methanol solutions applied as a foliar spray or via irrigation were investigated in maize plant. Little differences of plant height were found among treatments and control. The leaves from corn plants sprayed continuously with aqueous methanol solutions or water for several weeks were differently consumed by H. armigera larvae. The 3rd and the 4th instar larvae preferred consuming the leaves sprayed with methanol solutions. And the larvae fed on methnol solution-sprayed leaves gained more body weights.Methanol, formaldehyde and formic acid affected corn seed germination. At the concentration of 0.005%, aqueous methanol solution slightly improved germination and the rate germination, stimulated seed growth and development, enhanced seed vigor index, compared with control seeds. In contrast, at higher concentrateion, aqueous solutions of methanol, formaldehyde and formic acid inhibited seed germination.The maize seeds sterilized by 0.5% sodium hypochlorite (NaClO) solution killed all pink-pigmented facultative methylotrophic bacteria. The germination of treated seeds were slower, the seed vigor index were clearly decreased. 0.005% aqueous methanol solution did not improve the germination of treated seeds. Addition of aqueous gibberellin or auxin solution improved the germination of control seeds but not treated seeds. These results suggested that the application of methanol at lower concentration increased the pink-pigmented facultative methylotrophic bacteria population, which further stimulated corn seed germination. Methanol, formaldehyde and formic acid at higher concentration decreased water absorption by corn seed, inhibited seed germination. Addition of liquid gibberellin can partially compensated these negative effects. These indicated that methanol, formaldehyde and formic acid may eventually become formic acid in corn seed, and formic acid may esterized gibberellin to inactivated this hormone, and consequently inhibit seed germination.