Sat 18 October p5 Pablo G. Guerenstein

 

Passage 5

Passage 1 is adapted from Pablo G. Guerenstein et al., “Floral CO2 Emission May Indicate Food Abundance to Nectar-Feeding Moths.”02004 by Springer-Verlag. Passage 2 is adapted from Elia Ben-Ari, “Better Communicating through Chemistry:’ ©2008 by American institute of Biological Sciences.

Passage 1

The ability to sense subtle variations in ambient CO2 concentration is well established among moths. CO, receptor cells are located in a sensory organ, the labial-palp pit organ (LPO). Morphological studies have shown that this organ contains up to 2,000 receptor cells, and physiological experiments have revealed that those sensory cells respond specifically to CO2 with high sensitivity. For most species of moths, however, the roles of sensory information about ambient CO2 are unclear.

The existence of CO2 gradients in their natural habitats has led to several hypotheses about the significance of CO2 information for moths. The strongest evidence for the use of CO2 information by moths came from a study of the use of local CO2 gradients by adult Cactoblastis cactorum. The LPO of C. cactorum is larger in females than in males, and it was suggested that probing the surface of host plants with the labial palps might inform female moths about metabolically more active parts of the plants in order to identify high-quality oviposition sites [locations to lay eggs].

In the hawkmoth Manduca sexta, the LPO is large and apparently not sexually dimorphic, suggesting that in this species, CO2 information could be similarly important for both males and females. We speculated, therefore, that information about ambient CO2 could be valuable for functions other than, or in addition to, oviposition. Manduca species, which feed as adults, possess a more elaborate LPO than that of moths that do not feed as adults. We hypothesize, therefore, that Manduca might use its CO2-sensing system to detect the high metabolic activities of flowers and thus to locate profitable nectar sources.

Passage 2

When the hawkmoth Manduca sexra catches scent of a flower on which it can feed, it flies in a zigzag pattern as it tracks the odor to its source. Then, hovering over the bloom like a helicopter, the month extends its long proboscis to probe the flower and dine on nectar.

As in other pollinator-plant interactions, the hawkmoth uses cues such as flower color, shape, fragrance, and texture to find and evaluate Dowers as potential food sources. But recent studies suggest that floral carbon dioxide (CO2), which is associated with nectar production and increased respiratory activity, may also play a role in interactions between flowers and their insect pollinators.

In the Sonoran Desert, the hawkmoth is the primary pollinator of the night-blooming Dotura wrighrii. Datura’s large white flowers open explosively at dusk, releasing CO2 at concentrations much higher than ambient levels. Manduca sexra moths have a special G02-sensing organ, and a 2004 study showed that male hawkmoths wilt choose an artificial flower emitting higher than ambient CO2 levels over one emitting ambient levels.

In a paper published in 2008, Cornell University doctoral student Joaquin Goyret and colleagues provided new details on how floral CO2 affects the behavior of both male and female M. sexta moths. Goyret, Poppy Markwefl, and senior author Robert Raguso examined the behavioral responses of hawkmoths to scentless white paper flowers and to paper flowers with a floral scent, with CO2 or with both scent and CO2. They found that CO2 like floral odor, attracted male and female moths from a distance and elicited the characteristic zigzag tracking behavior. But CO2 did not trigger flower-probing behavior.

Surprisingly, when moths were given a choice between a fake flower emitting floral scent alone and an identical flower emitting scent plus CO2 the males preferred scented flowers with high CO2 levels, but females chose randomly. “That’s when we started putting things together,” Goyret says. Other researchers had observed that female hawkmoths, which lay their eggs on the underside of leaves, often feed and lay eggs on the same host plant in a single visit if the plant has nectar-rich flowers. So Goyret. and coworkers added odors from host-plant leaves to the mix in their choice experiments with fake flowers. “Now the females also started choosing the flowers emitting high levels of CO2, ” he says; Taken together with observations by others that female M. sexta lay more eggs on plants with experimentally increased amounts of nectar, the new findings suggest that female moths are using CO2 as distance cue to find plants that not only are a good source of nectar but also will be high-quality hosts for their egg and larvae.

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