Infective juveniles (IJs) of Steinernema carpocapsae (All) are
able to remain relatively highly infective even when they have
almost exhausted their neutral lipid reserves. This is not seen in other
steinernematid species so we proposed that
carbohydrate may be important for infectivity in aging IJs of S.
carpocapsae. The present study investigated glycogen
utilization in IJs of 4 entomopathogenic nematodes, S. carpocapsae,
S. riobravis (Biosys 355), S. feltiae (UK76) and S.
glaseri (NC), stored in distilled water at 25 °C. The 4 species had
appreciable amounts of glycogen; from ca. 8% dry
weight in S. riobravis to ca. 18% in S. glaseri.
Infective juveniles of S. carpocapsae and S. riobravis survived
for 120–135
days and utilized ca. 90% of their glycogen reserve at an almost
constant rate during a 112-day storage period. Steinernema
feltiae and S. glaseri lived for much longer (>450 days) and
during a 250-day storage period their glycogen content
decreased by 27 and 40%, respectively. In contrast to the other 3 species, the
rate of lipid decline preceded that of glycogen
in S. carpocapsae. The rate of glycogen decline in S. carpocapsae
IJs incubated with the glycolytic inhibitor, iodoacetamide
(10−4M) was significantly reduced
(P<0·05)
compared with untreated nematodes, and the infectivity of inhibitor-treated
aged (>80 days) IJs was reduced compared with controls. Incubating aged
(80-day) IJs of S. carpocapsae (mean neutral
lipid content ca. 10% of initial level) with
10−4M
iodoacetamide for 24 h significantly reduced (P<0·05) their
infectivity
compared with freshly harvested inhibitor-treated IJs and untreated controls.
Following an 11-day recovery period, the
infectivity of inhibitor-treated aged IJs recovered significantly
(P<0·05). The evidence suggests that glycogen is an
important source of energy for maintaining infectivity in aged IJs of S.
carpocapsae.