Hornworms, tobacco

Human Chimpanzee Sheep Rattlesnake Carp Garden snail Tobacco hornworm moth Baker s yeast (iso-1) Cauliflower... 

Yellow-striped army worm (28) Tobacco hornworm (3)... 

The larvae that hatch from Cotesia eggs remain inside their caterpillar host, exploiting it as a secure haven from the outer world and a convenient food supply. They feed on the caterpillar from within until they are mature and ready to pupate. Then they emerge from its body and immediately begin spinning small white cocoons, which they attach by one end to the caterpillar s back. It is not uncommon for a tobacco hornworm, still alive, to be festooned with fifty or more Cotesia cocoons, each resembling a diminutive grain of rice fastened to the caterpillar. Each cocoon contains... 

The combination of the wasps own toxins and those provided by the virus affect tobacco hornworms in other ways as well. One of these is to modify their behavior to the wasps benefit. Parasitized caterpillars continue to feed and behave normally until about eight hours before the larvae emerge. At that time, the caterpillars cease to eat and crawl about. They show no other deficiency and their reflexes appear normal. The details of this modification are uncertain, but it appears to favor the wasp larvae. A normal, unparasitized caterpillar readily eats wasp pupae offered to it. This implies that an active caterpillar would be a threat to larvae emerg-... 

Octopamine in the CNS. It is reasonable to suppose that this handful of varied systems where OA has effector functions is only the tip of the iceberg and that more will be discovered. All of these known systems are located peripherally since the demonstration of a specific transmitter role for any compound within the CNS is very challenging. However, there is every reason to believe that OA has important transmitter or modulator functions in the CNS of arthropods. It is synthesized and stored there in plausible amounts (8,9f13) and OA-sensitive adenylate cyclase activity has been found within the CNS of several arthropods. In addition to the examples cited in the recent review by Bodnaryk (26), this activity has been demonstrated in the tobacco hornworm (27f28), Drosophila melanogaster (29)t the tick, Amblyomma hebraeum (27) and the crayfish (30,31) Neurones specifically sensitive to OA have been... 

The 29-fluorophytosterols, members of a new class of selective pro-insecticides, have been synthesized and examined m vivo in tobacco hornworms. Dealkylation at C-24 of the steroid side chain by insects releases the latent poison fluoroacetate, resulting in dose-dependent reductions in growth rate, maximum weight, and survival when fed at 1 to 100 ppm to Manduca sexta. 

The 29-fluorophytosterols (Fig. 3) all showed significant impairment of growth and development of larval tobacco hornworms when fed at 1 to 100 ppm to Manduca sexta. It is clear that the A22 sterols and were more toxic and caused more severe... 

Cuticular diterpenes-duvanes and labdanes. Cutler have found that the cuticular diterpenes of green tobacco have both allelopathic and insect-deterrent effects (38). Present in the cuticle are duvane and/or labdane diterpenes (Figure 3) The levels of these specific cuticular components are believed to be responsible for the observed resistance of some types of tobacco to green peach aphids Myzus persicae (Sulzer), tobacco budworm Heliothis virescens (F.), and tobacco hornworm Manduca sexta (L.) (39). 

We initiated this line of research by testing isolated compounds for their effects upon two Insects, the grasshopper (Melanoplus bivitattus or 11.. sanouinipes) and the tobacco hornworm, Manduca sexta. We could thereby test for activity against adult... 

The tobacco hornworms are observed over a seven-day period for signs of toxicity, reduced feeding, relative weic t gain (compared to controls) and ability to shed exuvia (ecdysis). 

Grasshoppers, however, wreak their damage as adults, while the great majority of agricultural damage is done by larval stage insects. The tobacco hornworm has served as a laboratory model for insecticidal screening (15). 

The other two Dvsldea metabolites tested, 5-acetoxy- and 5-hydroxy-nakafuran-8, 7 and 8, exhibited a different activity profile against the grasshopper. The acetate 7 was toxic at the high dose and antifeedant at the lesser dose, while the alcohol 8 was antifeedant at both doses. Surprisingly, the acetate 7 exhibited no activity in the tobacco hornworm assay. 

These same two diterpenes were subjected to the tobacco hornworm assay. Brlantheln Y, 10, was quite toxic at 250 ppm, killing the exposed larvae within thirty hours. There appeared to be no inhibition of feeding. On the other hand, the less functionalized brlanthein W, 12, elicited only 50 percent mortality over five days, and the surviving larvae suffered from extremely poor weight gains (only 6J of controls) despite feeding freely on the treated diet. 

The tobacco hornworm assay is quite amenable to the screening of crude extracts for Insect control activity. Table IV summarizes the results obtained to date. Most noteworthy is that the aqueous extracts tend to be inactive nearly all the activity, observed in the form of toxicity and/or weight gain inhibition, resides in organic extracts. In the limited sampling conducted thus far, sponges would appear to exhibit the best activity in the assay. 

Plants that produce "specific toxins may be plagued by Insects that develop a tolerance to these toxins in much the same way as Insects develop tolerance to synthetic insecticides. Two examples from this chapter are the tobacco hornworm and the boll weevil which have developed a high tolerance to nicotine and gossypol, respectively. Some occurrence in the distant past may have placed sufficiently high selection pressure on these Insects that they developed tolerance to these compounds. Alternatively, the same effect could have occurred by a low selection pressure applied over a very long period time. Other plants protect themselves by employing general" toxins. 

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. 

Experiments conducted with the tobacco hornworm, Manduca sexta and the aquatic plant, Lemna minor are consistent in finding that canavanine does not affect whole organism ability to incorporate [ Hjleucine into trichloroacetic acid-insoluble materials (see Table I). Such determinations evaluate the balance between reactions fostering protein synthesis and those responsible for the turnover and degradation of proteins. If the treatment time is reduced to 30 min, so as to accentuate synthetic reactions over those of catabolism, the result is the same. 

Studies of canavanine interaction with the tobacco hornworm and J-. miTior also revealed the marked ability of canavanine.to inhibit whole organism incorporation of [ Hjthymidine and uridine into trichloroacetic acid-precipitated materials. When canavanine is provided simultaneously with the appropriate radio-labeled precursor, ample evidence for curtailed nucleic acid metabolism emerges but protein synthesis is unaffected (Table I, exp. I). In experiment II, canavanine is allowed to assimilate... 

In experiment A, newly ecdysed fifth stadium tobacco hornworm larvae received 5 jiCi of labeled compound and 1 mg canavanine/g fresh body weight. Three hrs later, the treated larvae were collected and processed. In experiment B, canavanine was injected first and 24 hrs later, the labeled compound was administered. All larvae were collected and processed 3 hrs later (from the work of Rosenthal and Dahlman). 

Examination of this question with the tobacco hornworm, an insect known to be canavanine-sensitive (this insect normally feeds on canavanine-free plants) revealed that it readily incorporates [ C]canavanine into its newly synthesized proteins. Caryedes brasiliensis. however, very effectively avoids the production of such radiolabeled proteins. When the arginyl- RNA synthetase activity of these insects was compared, tobacco hornworm larvae readily activated canavanine while the larvae of the bruchid beetle possess an arginyl- tRNA synthetase with a marked ability to discriminate between arginine and its structural analogue (22). 

Little is known of canaline toxicity in whole animals or plants. Canaline-fed tobacco hornworm larvae grew poorly, exhibited much more deformity, and succumbed in larger numbers than the controls (8). This ornithine analogue is neurotoxic to the adult moth where it induces almost continuous motor activity. 

The wild tomato, Lycopersicon hirsutum f, glabratum is covered with trichomes which contain 2-tridecanone. The level of this compound is much lower in the domesticated tomato, U esculentum. This exudate proved to be toxic to Manduca sexta (tobacco hornworm) and to Heliothis zea (121). The density of glandular trichomes, which secrete 2-tridecanone, was influenced... 

Morgan, A. and Lyon, S. (1928). Notes on armyl salicylate as an attractant to the tobacco hornworm moth. Journal of Economic Entomology 21 189-191. 

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