JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org. This content downloaded from 134.Abstract. Temperature and food quality are well known to constrain the growth of insect herbivores, but less is known about how these factors may interact. We examined the effects of three tomato allelochemicals (chlorogenic acid, rutin, and tomatine) and two thermal regimes (210: 10?C and 26?: 15?C, representing spring and summer respectively) on three insect herbivores: a Solanaceae specialist, Manduca sexta, and the polyphagous Helicoverpa zea and Spodoptera exigua.The alkaloid tomatine slowed development of the polyphagous H. zea, but the two phenolics had little effect. Development of the polyphagous S. exigua was faster with tomatine at the cool thermal regime, and slower with the two phenolics together at the warm thermal regime. All three of the tomato allelochemicals slowed development of the specialist M. sexta.Values of approximate digestibility (or assimilation efficiency) for the two polyphagous species spanned a range twice that of the Solanaceae specialist, increasing when allelochemicals were added to diet. Our techniques permitted us to separate pre-and post-ingestive effects of allelochemicals on mass gained, but we found complex interaction of allelochemicals and of temperature and allelochemicals.The effects of an allelochemical on larval performance often depended on the combination of other allelochemicals in the diet. But the allelochemicals did not always have a negative effect, and multiple allelochemicals did not always have a more negative effect than a single allelochemical.Interaction between thermal regime and the allelochemicals was also common. For example, whether rutin had a negative, neutral, or positive effect on relative growth rate of S. exigua depended on thermal regime and presence or absence of chlorogenic acid. Often the negative effect of an allelochemical was greater at the warm regime than at the cool regime, but not consistently so.Another experiment showed that thermal regime did not affect allelochemical concentration in the diets. Over time (7 d), only tomatine concentration declined. Therefore, the interactive effects of thermal regime and allelochemicals on the insect herbivores were not an artifact of the experimental procedures.Overall, the results indicated that insect performance is not a simple function of temperature and food quality because interactions occur between these factors. They also suggest that the array of chemical defenses exhibited by a particular plant species may be shaped in part by temperature altering the efficacy of allelochemicals.
Abstract. The behavioural mechanisms driving compensatory food consumption in response to dietary dilution as well as the relationship between feeding time and food residence time (i.e. digesta retention time in the gut) were studied using the non‐diapausing strain of the grasshopper Melanoplus differentialis (Thomas) (Orthoptera: Acrididae). 3‐day‐old, sixth‐instar nymphs and 3‐day‐old adults were fed artificial diets containing 1%, 3% and 5% total nitrogen (N) at 30d̀C, LD 14:10h; the feeding behaviour was recorded using electronic monitoring devices connected to microcomputers for 24 h. The percentage of time spent feeding increased linearly as diets were diluted using non‐digestible cellulose from 5% to 1% N. This response was due to an increase in the number of meals while the meal duration of a feeding bout was unaltered. Sixth‐instar nymphs spent about 40% more time feeding than the larger adults. The increased feeding time in nymphs resulted from both more frequent feeding bouts and longer meal duration. Feeding time and food residence time were highly negatively related.
One effect of global warming may be an increase in night-time temperatures with daytime temperatures remaining largely unchanged. We examined this potential effect of global warming on the performance of tobacco hornworm larvae, Manduca sexta (Sphingidae), by manipulating night-time temperature and dietary rutin levels simultaneously under a 12 light:12 dark photoregime. All four thermal regimes (26:14, 26:18, 26:22, and 26:26° C) had a daytime temperature of 26° C, with the night-time temperature increased from 14 to 26° C by increments of 4° C. Dietary rutin levels (0, 10 and 20 μmoles g fresh weight of diet) reflected those occurring naturally in the leaves of tomato, a preferred host plant of M. sexta. With low night-time temperatures (14 and 18° C), rutin had a negative linear effect on developmental rate, relative growth rate and relative consumption rate of the caterpillars. However, at a night-time temperature of 22° C, rutin had a negative non-linear effect. At a night-time temperature of 26° C, rutin had a negative linear impact but less so than at the other nightime temperatures. Likewise, the negative effect of rutin on molting duration was mitigated as night-time temperature increased. Final larval weight decreased linearly with increased dietary rutin concentrations. Total amount of food ingested was not affected by either rutin or thermal regime. As expected, the caterpillars developed faster under an alternating 26:14° C regime than a constant 20° C regime (the average temperature for the alternating regime), but the effect of rutin depended on the thermal regime. Switching daytime and night-time temperatures had no statistically significant effect on caterpillar performance. Overall, the effect of rutin on rates of larval performance was greater at some levels of warmer nights but damped at another level. These results indicate that the potential effect of warmer nights on insect performance is not a simple function of temperature because there can be interactions between night-time temperature and dietary allelochemicals.
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