Life history and fat reserves of the predator Podisus maculiventris (Heteroptera: Pentatomidae) under low inputs of the prey Epilachna varivestis (Coleoptera: Coccinellidae)
Abstract
The objective of my research was to study the life history of female Podisus maculiventris (Say) and how it allocates food reserves between metabolic and reproductive needs under low prey inputs. I also studied the effect of maternal diet, maternal ages, and nymphal diet on developmental time and survivorship of nymphs of P. maculiventris reared under low inputs of prey. The life history traits that I measured included longevity, fecundity, numbers of eggs stored in ovarioles, and fat reserves. One-day old, unmated females were fed Mexican Bean Beetles, Epilachna varivestis (Mulsant), under (a) low prey, (b) high prey and (c) initially low then high prey inputs. The females were sacrificed and dissected at different ages to determine the effect of age on fat reserves and reproduction. I measured fat reserves as the amount of lipids in the fat body. I found that under low rates of predation, Podisus maculiventris maintains its survival but at the expense of reproduction. Developmental time of nymphs was shorter and survivorship was higher if they were well-fed, and they came from well-fed and young mothers than if they were poorly-fed and reared from poorly-fed and older mothers. As the time interval between feedings increased, the amount of lipids increased, and the number of oviposited eggs decreased. When starved individuals were given food, the rate of egg production increased. These findings indicate that lipids were stored in greater amounts to maintain longevity and that proteins from animal prey were important for egg maturation and subsequent oviposition. Thus, under low food conditions, lipids are apparently channeled to fat for survival, and only with sufficient fat reserves will reproduction begin to increase. This pattern may explain the indirect life history trade-off between survival and reproduction and the physiological trade-off between lipid reserves and reproduction. Adaptations to low prey inputs may explain why P. maculiventris persists in various environmental conditions, including those characterized by scarce and/or unpredictable food conditions.
Degree
Ph.D.
Advisors
O'Neil, Purdue University.
Subject Area
Entomology
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