Trade‐offs in host use by Manduca sexta: plant characters vs natural enemies

Abstract

There are two principal native host plants for the sphingid moth Manduca sexta L. in south eastern Arizona: Datura wrightii (Solanaceae), and the more recently reported, nonsolanaceous host, Proboscidea parviflora (Martyniaceae). A comparative study on causes and rates of mortality was conducted, since this provided a “natural experiment” for examining potential trade‐offs in host use. The field data identified a dramatic trade‐off between plant quality and predation. D. wrightii appears to provide a high quality food source in growth experiments, and eggs laid on its leaves hatch at high rates. The eggs and larvae, however, underwent extremely high levels of predation and parasitism in the field, and fewer than 0.5% reached the final larval stage. Eggs laid on P. parviflora, on the other hand, suffered low levels of predation and virtually no parasitism, but many eggs did not hatch due to developmental abnormalities induced by the plant, while a large proportion of larvae died after a few days of feeding. Overall, 3% of the eggs reached the final stage on this plant. The maintenance of the two host plants cannot be explained by single factors, but rather by the outcome of multiple factors on the insect fitness, including plant quality, suitability for egg development, predation risk, plant availability and competition with other herbivores. Our data emphasize the importance of predation in shaping host‐plant ranges and support the idea of host‐specific predation rates and “enemy‐free” space.

Enemy-free space maintains swallowtail butterfly host shift

“…Only three studies have satisfactorily established the occurrence of EFS, but they have been agricultural systems (22,23) or artificial host shifts (24). Other studies suggest EFS but did not satisfy all three of the hypotheses proposed by Berdegue et al (12,18,(25)(26)(27)(28)(29)(30). In particular, the third hypothesis is often difficult to test (18) because costs are often difficult to find or may have disappeared if the host shift occurred in the distant past.…”

Coexisting generalist herbivores occupy unique nutritional feeding niches

“…For example, differences in nutritional niches may alter the population-level responses of prey to generalist predators when available food quality varies if apparent competition is operating (43) by altering the relative susceptibility of each species depending on current conditions. Knowing the parameters of the nutritional niche will make the outcomes of such interactions more predictable (44,45) as both top-down and bottom-up forces combine in subtle ways to determine the outcomes. Moreover, the observed buffering capacity to performance over a range of protein-carbohydrate foods may further reflect the ability to deal with unpredictable nature of food resources, the impact of nonlethal encounters with predators reducing overall consumption, or both.…”

Influence of Green Leaf Herbivory by Manduca sexta on Floral Volatile Emission by Nicotiana suaveolens

“…plants are Nicotiana attenuata (Voelckel and Baldwin, 2004), Datura wrightii (Mira and Bernays, 2002), and the more recently discovered nonsolanaceous Proboscidea parviflora (Martyniaceae; Mira and Bernays, 2002), but as an oliphagous specialist, M. sexta accepts solanaceous plants in general (del Campo and Renwick, 1999;Voelckel and Baldwin, 2004). However, to assess and compare the susceptibility to M. sexta, the green leaf response of N. suaveolens was scrutinized.…”