Generalist Insect Predators Research Articles

RESPONSE OF AN INSECT PREDATOR TO PREY FED MULTIPLE ALLELOCHEMICALS UNDER REPRESENTATIVE THERMAL REGIMES

We examined the effects of three allelochemicals found in tomato (chloro- genic acid, rutin, and tomatine) and two thermal regimes (210:100C and 260:15'C, repre- senting spring and summer, respectively) on the performance of a generalist insect predator (Podisus maculiventris: Pentatomidae) fed prey containing those allelochemicals. The prey were Manduca sexta (Sphingidae) caterpillars, Solanaceae specialists with a preference for tomato. Whether an allelochemical had a negative, neutral, or positive effect on develop- mental time or mass gained by the predators depended on thermal regime and the com- bination of allelochemicals in the prey's diet. The effects of multiple allelochemicals were not always additive. For the most part, the allelochemicals had greater negative effects at the warmer thermal regime. Effects of allelochemicals also depended on the stage of the predator. Individually, chlorogenic acid and rutin prolonged developmental time of second- instar nymphs. In contrast, only rutin and tomatine together affected developmental time of fourth-instar nymphs, and this combination of allelochemicals reduced developmental time. Tomatine substantially reduced mass gained by second-instar nymphs but had no effect on mass gained by fourth-instar nymphs. Rutin and tomatine together had no effect on second-instar nymphs but increased the mass of fourth-instar nymphs. There were no allelochemical by temperature interactions for second-instar nymphs, whereas allelochem- ical by temperature interactions influenced stadium duration, final dry mass, and relative growth rate of fourth-instar nymphs. Rutin and tomatine together eliminated the negative effect of chlorogenic acid on consumption of prey by the fourth-instar nymphs. Chlorogenic acid by itself and rutin and tomatine together increased the efficiency of conversion of ingested prey to nymphal biomass. Comparison with an earlier study revealed that the effects of these thermal and dietary conditions were distinctly different for prey and pred- ators, which suggests that such conditions would promote developmental asynchrony be- tween prey and predator populations.

Allelochemicals in Tomato Leaves Affect a Specialist Insect Herbivore Manduca sexta Negatively but with No Ill Effects on a Generalist Insect Predator, Podisus maculiventris

To understand the role of allelochemicals in tritrophic interactions, it is important to consider how allelochemicals affect both insect herbivores and their predators. In one experiment, a specialist insect herbivore (Manduca sexta: Sphingidae) was fed artificial diet either without allelochemicals, or containing a combination of allelochemicals found in tomato leaves (tomatine, rutin and chlorogenic acid). When fed artificial diet containing allelochemicals, the herbivores consumed less food, their developmental time was extended and their final weight was lower than those fed artificial diet without allelochemicals added. In another experiment, a generalist insect predator (Podisus maculiventris: Pentatomidae) was given prey (M. sexta) fed artificial diet either without allelochemicals, or with the combination of allelochemicals. The allelochemicals in prey diet did not affect nymphal growth, nymphal survivorship, adult female longevity, number of eggs produced, number of egg masses produced, developmental period of the eggs, viability of the eggs, or weight of the first instar progeny. Thus, this study documents a case in which a plant would benefit by producing allelochemicals because the specialist herbivore would consume less plant material and by ingesting the allelochemicals have poorer growth, and the predator would be unharmed by the presence of allelochemicals within the diet of its prey.

Combined effects of allelochemical‐fed and scarce prey on the generalist insect predator Podisusmaculiventris

1. The simultaneous effects of allelochemicals ingested by herbivorous insect prey and prey scarcity on the performance of a generalist insect predator were examined.2. Fifth‐instar predatory stinkbugs (Podisusmaculiventris: Pentatomidae) were fed caterpillars (Manducasexta: Sphingidae) in three prey scarcity treatments: every day (unlimited amount), one caterpillar every third day, one caterpillar every fifth day. The caterpillars were fed either a plain diet or a diet containing rutin, chlorogenic acid and tomatine, which are three of the major allelochemicals in tomato leaves (Lycopersiconesculentum: Solanaceae), the preferred food of these caterpillars.3. Food consumed, efficiency of conversion of ingested food to biomass (ECI), biomass gained, stadium duration and relative growth rate (RGR) of predators were negatively affected by prey scarcity. The allelochemicals negatively affected food consumed and ECI.4. There were prey scarcity by allelochemical interactions for ECI, biomass gained and RGR. For ECI, the allelochemicals had a greater negative impact on the predatory stinkbugs when prey were scarce. When prey diet contained allelochemicals, biomass gained and RGR declined more steeply with increased prey scarcity. There was an allelochemical by predator gender interaction for biomass gained. Allelochemicals had no effect on biomass gained by female stinkbugs, whereas biomass gained declined more steeply with increased prey scarcity for male stinkbugs fed caterpillars containing allelochemicals than for males fed control caterpillars.

Effects of chlorogenic acid-and tomatine-fed caterpillars on the behavior of an insect predator

If generalist insect predators are a selective force contributing to patterns of feeding specialization by insect herbivores, then predators should be deterred from eating allelochemical-fed prey. The attack and feeding behaviors of naive predators (Podisus maculiventris stinkbugs) reared on control caterpillars (Manduca sexta) fed plain diet were compared to experienced predators reared on caterpillars fed tomato allelochemicals. Tomatine-fed prey were found more quickly by both naive and tomatine-experienced predators, and chlorogenic acid-experienced predators were more stimulated to begin searching for prey. However, experienced predators were less likely to attack both chlorogenic acidfed and tomatine-fed caterpillars than were naive predators. These results indicate that allelochemical-fed prey were easier for predators to locate, but allelochemical-containing prey often deterred predation by experienced predtors.

Influence of intraguild predation among generalist insect predators on the suppression of an herbivore population.

We evaluated the influence of intraguild predation among generalist insect predators on the suppression of an herbivore, the aphid Aphis gossypii, to test the appropriateness of the simple three trophic level model proposed by Hairston, Smith, and Slobodkin (1960). We manipulated components of the predator community, including three hemipteran predators and larvae of the predatory green lacewing Chrysoperla carnea, in field enclosure/exclosure experiments to address four questions: (1) Do generalist hemipteran predators feed on C. carnea? (2) Does intraguild predation (IGP) represent a substantial source of mortality for C. carnea? (3) Do predator species act in an independent, additive manner, or do significant interactions occur? (4) Can the experimental addition of some predators result in increased densities of aphids through a trophic cascade effect? Direct observations of predation in the field demonstrated that several generalist predators consume C. carnea and other carnivorous arthropods. Severely reduced survivorship of lacewing larvae in the presence of other predators showed that IGP was a major source of mortality. Decreased survival of lacewing larvae was primarily a result of predation rather than competition. IGP created significant interactions between the influences of lacewings and either Zelus renardii or Nabis predators on aphid population suppression. Despite the fact that the trophic web was too complex to delineate distinct trophic levels within the predatory arthropod community, some trophic links were sufficiently strong to produce cascades from higher-order carnivores to the level of herbivore population dynamics: experimental addition of either Z. renardii or Nabis predators generated sufficient lacewing larval mortality in one experiment to release aphid populations from regulation by lacewing predators. We conclude that intraguild predation in this system is wide-spread and has potentially important influences on the population dynamics of a key herbivore.