Mexican bean beetle varivestis

FIGURE 2 Glandular hairs on surface of pupa of the Mexican bean beetle, Epilachna varivestis. The secretory droplets contain such azamacrolides as ep-ilachnene (27). (Bar = 0.1 mm.)... 

Microscopic examination showed the pupae of the Mexican bean beetle Epilachna varivestis to be covered with glandular hairs, each having a droplet of oil at its tip. Attygalle and co-workers undertook a chemical analysis of this secretion, which resulted in the identification of a novel family of alkaloids, the azamacrolides [40]. Five compounds (27-31) (Fig. 6) were identified by GC-EIMS from the secretion, with epilachnene (27) comprising over 90% of the volatile material. 

The antiherbivory effects of phytoalexins have been studied in our laboratory using the Mexican bean beetle and the soybean looper (44). The Mexican bean beetle, Epilachna varivestis. is an oligophagous species that feeds preferentially on legume hosts. 

The compounds were evaluated for insecticidal and acaricidal activity against the following species cabbage looper (Trichoplusia ni [Hubner]), Mexican bean beetle (Epilachna varivestis Muls), southern armyworm (Spodootera eridania [Cram]), pea aphid (Acvrthosiphon pisum [Harris]), twospotted spider mite (Tetranvchus urticae [Koch]) and southern corn rootworm (Diabrotica undecimpunctata Howardi). 

Dihydropinidine (189), along with 191, 196, and an alcohol from reduction of 191, has been isolated from the Mexican Bean Beetle Epilachna varivestis and was identified using GCMS [468], In a recent synthesis, racemic 189 was prepared from 4-methoxypyridine [469]. 

Additional 2,6-disubstituted piperidine alkaloids detected in Picea and Pinus include pinidinone and epipinidinone (191 and 194, from Picea pungens), 193 (from Picea abies, P. pungens), 195 (from Pinus nigra, P. sylvestris, P. ponderosa) and 196 (from Picea pungens, Pinus ponderosa, P. sylvestris, P. nigra)[467]. Pinidinone, an alcohol from reduction of pinidinone, and 196 have also been detected in the Mexican Bean Beetle, Epilachna varivestis [468]. 

In the Mexican bean beetle Epilachna varivestis, A -sterols were readily reduced to stanols, and the stands produced were then dealkylated to cholesterol. Significant amounts of lathosterol (7-dehydrocholestan-3 -ol) are also produced from cholestanol in this insect [165-167]. 

During an infestation by larvae of the Egyptian cotton leafworm Spodoptera littoralis (Boisd) in the summer of 1978, it was noticed that shrubs of Physalis peruviana L. (cape gooseberry) were not attacked, whereas other Physalis and Nicandra spp. suffered heavy damage. Asher and co-workers demonstrated that withanolide E (118) and 4(3-hydroxywithanolide E (119), isolated from P. peruviana, as well as several related steroids, had insect antifeedant properties. Further studies on other withanolides showed antifeedant effects and species-specific activity on three insects, S. littoralis (Boisd.) (Lepidoptera), the Mexican bean beetle, Epilachna varivestis Muls. (Coleoptera) and the red flour beetle, Tribolium castaneum (Herbst) [62]. 

Differences in the transport and metabolism do not seem to play an important role in tebufenozide s lack of toxicity to coleopteran species. Studies in which a highly susceptible caterpillar species (Spodoptera eridania) and a non-susceptible larval beetle species (Mexican bean beetle, Epilachna varivestis) were fed equal amounts of Relabelled tebufenozide showed surprisingly similar patterns of tebufenozide uptake, metabolism, and overall tissue distribution (13). The minor differences observed in this study were clearly insufficient to account for the greater than 2,800-fold difference in tebufenozide susceptibility between these two species (LC50 = 0.7 ppm for Spodoptera, >2,000 ppm for Epilachna) (12). Studies comparing beet armyworm (Spodoptera exigua) with Colorado potato beetle (Leptinotarsa decemlineata) yielded similar results (15). 

Nayar, j. K. and G. Fraenkel, The chemical basis of the host selection in the Mexican bean beetle, Epilachna varivestis (Col-eoptera, Coccinellidae), Annu Ent. Soc. Am. 56, 174-178 (1963). 

Epilachnine is an example of a quite different substance made by a coc-cinellid beetle and derived from a fatty acid, although that origin might not be immediately obvious. It is the defensive secretion of the pupae of the Mexican bean beetle Epilachna varivestis. The pupae carry the toxin... 

Plate 4 Pupa of the Mexican bean beetle Epilachna varivestis, showing its many hairs with droplets of fluid containing epilachnine and related macrocyclic compounds and a close-up view of some of the hairs and droplets (Photo Maria Eisner)... 

In most cases of secondary protection of insect herbivores by alkaloids the source of the alkaloid is the herbivore diet, i.e. the plant host. There have been several interesting reports on the occurrence of chemical defenses of insects based on alkaloids actively synthesized or at least chemically modified by the insect. One such report showed that deterrence to predation by ants and spiders was afibrded to the Mexican bean beetle Epilachna varivestis) by the production of the homotropane alkaloid euphococcinine (66). This compound which actually may be a polyketide, is not present in the body of larvae or newly hatched adults but is accumulated in the beetles blood within one week of emergence. When attacked, the beetle reflex-bleeds emitting droplets of blood containing as much as 5 pg of euphococcinine. 

The larva of the Mexican bean seed beetle Epilachna varivestis excretes a protective secretion from its glandular hair. The active principle is the azamacrolide E. C16H29NO2, Mr 267.41, oil. The biosynthesis proceeds from oleic acid and L-serine. For absolute configuration (S) see Lit.. ... 

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