N. Gillyboeuf et al., 2 DIFFERENT COLD RESISTANCE STRATEGIES IN CORN BORING CATERPILLARS OFA SAME BIOTOPE, Bulletin de la Societe zoologique de France, 122(1), 1997, pp. 21-31
In the south-west of France (45N, 0) two species of moth larvae overwi
nter on corn stalks after harvesting: the European corn borer (ECB, Os
trinia nubilalis Hbn., Pyralidae) and the Pink corn stalk borer (PCSB,
Sesamia nonagrioides Lef., Noctuidae). ECB is able to resist to cold
temperatures as low as -20 degrees C, but PCSB does not survive temper
atures below -6, -8 degrees C. The aim of this study was to understand
how PCSB was able to survive even to the slightly lower temperatures
frequently encountered in this area of France, We used 2 approaches: i
) a biochemical analysis of cold-hardiness of PCSB using ECB as an exa
mple of strong cold resistance, ii) an ecophysiological study of PCSB
in its natural environment. Under cold temperatures both larvae are ab
le to synthesize cryoprotectors; PCSB and ECB accumulate small amounts
of hemolymph trehalose and huge amounts of hemolymph glycerol respect
ively. These differences can be explained by the changes in the activi
ties of two key enzymes of carbohydrates metabolism: Glycogen Phosphor
ylase (GP) and Phospho 6 Fructo 1 kinase(PFK). In ECB, GP is highly an
d continuously stimulated by low temperatures, producing large amounts
of phosphorylated glucose. This substrate is then used to synthesize
glycerol as a result of the stimulation of PFK by diapause and cold (t
he mechanism of PFK activation is very similar to that of the mammals)
. Conversely, in PCSB, GP is only weakly and transiently activated by
cold, producing low amounts of phosphorylated glucose over a short per
iod of time. Moreover PFK is inhibited and blocks the glycerol synthes
is pathway. The phosphorylated glucose is then used for the synthesis
of small amounts of trehalose by a PFK upstream pathway. Unlike ECB, d
iapausing larvae of PCSB are not able to resist cold as a result of a
biochemical adaptation. However they are able to escape cold by an unu
sual <<behavioral strategy>>. At The beginning of the fall, diapausing
larvae migrate into the roots of the corn plant, under the ground. Th
e microclimate of this particular site protects larvae against air tem
peratures as unfrequent as -15 degrees C (which are really seldom in t
his area of France). The results of this ecophysiological study have l
ead to the design of a non pollutant pest control method; after harves
ting and before winter, the corn roots are uprooted and laid on the gr
ound, where they are exposed to cold temperatures. For this purpose, a
new agricultural tool has been designed.