Behavioral manduca sexta

The host range of the tobacco hornworm (Manduca sexta) is limited to selected members of the family Solanaceae. In an effort to better understand the chemical basis for the host plant selection process, we have undertaken an examination of both hornworm preferred and non-preferred members of the Solanaceae. Our investigations have shown this tc be a complex system involving the subtle interaction between such behavioral modulators as (1) Ovipositional stimulants (2) Feeding stimulants and imprinters (3) Anti-feedants (A) Repel-lants (5) Insecticides. The results of these investigations will be discussed. 

L-canavanine and L-canaline. Secondary plant substances may evoke particular types of stereotyped insect behavior via actions within the CNS. An excellent example is the work of Kammer, Dahlman, and Rosenthal (40), who observed that injection of adult Manduca sexta with L-canavanine and L-canaline led, within minutes, to sustained flights lasting many hours. The site of action of L-canavanine and L-canaline was believed to be the CNS. This produced continuous motor output, which became less coordinated with time. L-canavanine and L-canaline are two of some 260 non-protein amino acids accumulated by various plants (41). If an unadapted insect acquired... 

Eclosion hormone (EH) is a novel insect neurohormone that acts on the nervous system to trigger a stereotyped set of behaviors. The gene that encodes EH was isolated from the moth Manduca sexta and has provided a molecular means to determine the structure of EHs from a variety of insects. Only a few (2-4) neurons in the CNS produce EH and these cells appear to release the peptide both locally within the CNS and systemically into the blood. The former is responsible for causing the behavioral responses while the latter acts on various peripheral targets. 

EH was initially identified as a circulating neuropeptide that was thought to act back on the CNS to trigger ecdysis behaviors. In pharate adult Manduca sexta. large amounts of EH accumulate in the CC-CA complex prior to ecdysis and are released into the hemolymph late in the molt. A set of laterd brain neurosecretory cells (NSCs) that projected to the CC-CA were found to contain EH-like activity CLL). It was clear, however, that these cells were not responsible for EH release in larvae or pupae since in these stages release of the hormone comes from the ventral nervous system Q). The recent discovery of the cells responsible for this release has prompted a re-evaluation of the route by which EH triggers ecdysis. 

It was mentioned earlier in this chapter that alkaloids have no selective toxicity to invertebrates. Therefore, for many insects, these compounds are more attractive than toxins (Figure 4.5). The cases of butterfly or beetle behaviors just mentioned are very evident examples of the importance of plants for invertebrates. In both cases, alkaloids are secondary compounds that take part in the attraction for feeding. Moreover, it is also known that Manduca sexta flourish on alkaloid-rich Nicotiana plants and bmchid beetles BrucMdius villosus) on quinolizidine-alkaloid-iich plants.Such examples are a consequence of the herbivore model for choosing a specific plant diet. This model is based on the plant-herbivore interaction. The plant alone can either attract or deter the insect adult or larvae. It is necessary to highlight that alkaloids represent only one group of the secondary compounds through which plants worldwide interact with insects and other animals. 

Stadler, E. and Hanson, F. E. (1976) Influence of induction of host preference on chemoreception of Manduca sexta Behavioral and electrophysiological studies. Symp, Biol, Hung, 16, 267-73. 

Analyses of solvent rinses of the pheromone glands from calling female tobacco hornworm moths, Manduca sexta (L.) revealed the presence of the following compounds 9 -16 AL, 11Z-16 AL, 11E-16 AL, 16 AL, 10E,12Z-16 AL, 10E,12E-16 AL, lOE,12E,14Z-16 AL, lOE,12E,14E-16 AL, 11Z-18 AL, 13Z-18 AL 18 AL and IIZ,13Z-18 AL. The two trienals (which are new compounds) were identified by mass and PMR spectral analyses and by ozonolysis. Three isomeric conjugated triene aldehydes, 10E,12 ,14Z-16 AL, 10E,12Z,14E-16 AL and 10E,12E,14E-16 AL, two of which are components of the sex pheromone, were stereoselectively synthesized. In a wind tunnel, male tobacco hornworm moths exhibited the same behaviors in response to a blend of all the synthesized components, the gland rinse, or a calling female. Both 10E,12Z-16 AL and lOE,12E,14Z-16 AL are required to stimulate males to complete the characteristic reproductive behaviors. 

Fraser AM, Mechaber WE, Hildebrand JG (2003) Electroantennographic and behavioral responses of the sphinx moth Manduca sexta to host plant headspace volatiles. J Chem Ecol 29 1813-1833... 

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