Two diet experiments addressed the effects of allelochemical-fed prey (Manduca sexta caterpillars), temperature, and gender on performance of the insect predator, Podisus maculiventris. Two of the major allelochemicals in tomato were used: chlorogenic acid and tomatine. Predator performance was negatively affected by both chlorogenic acid-fed and tomatine fed-prey, and there were allelochemical by thermal regime interactions for both. Relative consumption rate and growth rate decreased at the higher levels of tomatine at the warmer thermal regime (summer conditions) but were unaffected at the cooler thermal regime (spring conditions). At the cooler thermal regime, stadium duration was prolonged when the predators were given chlorogenic acid-fed prey, but at the warmer thermal regime there was no such effect. There were several effects of gender: biomass gained, food consumed, relative growth rate and efficiency of conversion of ingested food to biomass were higher for females than males. Furthermore, the effects of thermal regime and tomatine on food consumption and biomass gained differed for females and males. In general, the hypothesis that generalist insect predators may be a selective pressure shaping host plant range of insect herbivores was supported by these results. But the occurrence of allelochemical by thermal regime interactions means that it will be difficult to determine the relative importance of plant chemistry versus predators on patterns of feeding specialization by herbivores without taking into account a third factor, temperature.

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.

A series of experiments was conducted to ascertain the effects of temperature and allelochemicals on the performance of an insect herbivore, with the goal of methodically expanding the cumulative data set on interactive effects of temperature and allelochemicals. The allelochemicals examined were caffeine, chlorogenic acid, quercetin, tannic acid and tomatine with the thermal regimes 20:15 °C versus 30:15 °C. Growth, molting time and food utilization efficiencies of third instar tobacco hornworms (Manduca sexta (L.)) were measured. Our results indicated that reductions in developmental rate by the phenolics were primarily due to effects occurring around and during molt initiation, that different phenolics may affect molt processes differently, and that some of the effects of the phenolics were a function of temperature, with greater negative effects at cool temperature. Negative effects of caffeine were most pronounced earlier in the stadium rather than during molt processes and, for some variables, the effect of caffeine was also a function of temperature.

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