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The infectivity of Steinernema carpocapsae dauer larvae (infective juveniles) remained nearly constant up to 60 days of storage in water at 25°C and then declined rapidly over the next 30 days. Few individuals remained infective after 120 days. Concurrent measurements showed that the mean neutral lipid content of individual S. carpocapsae declined to about 10% of initial levels after 60 days, and staining of individual nematodes with Oil Red O indicated that the population was almost homogeneous for low levels of neutral lipids. In contrast, the mean glycogen content of S. carpocapsae only declined significantly between 60 and 90 days of storage. These results show that the decline in infectivity in S. carpocapsae is correlated primarily with the decline in glycogen reserves and suggests that glycogen is the key late energy store in aged infective juveniles. In contrast, Steinernema feltiae dauer larva showed a much more gradual decline in infectivity over a 150- to 180-day storage period with a concurrent decline in neutral lipids, whereas glycogen levels declined up to 90 days of storage and then remained nearly constant. Thus, unlike S. carpocapsae , neutral lipids remain an important energy store in S. feltiae during storage, although glycogen also appears to be important, at least initially. |
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