Steroids beetles

Bark beetles primarily utilize isoprenoid derived pheromones [100,101] and have been the most studied regarding their biosynthesis [8,98]. Earlier work indicated that the isoprenoid pheromones could be produced by the beetle altering host derived isoprenoids however more recent work indicates that for the most part bark beetles are producing pheromones de novo. The production of isoprenoids follows a pathway outlined in Fig. 4 which is similar to the isoprenoid pathway as it occurs in cholesterol synthesis in mammals. Insects cannot synthesize cholesterol but can synthesize farnesyl pyrophosphate. Insects apparently do not have the ability to cyclize the longer chain isoprenoid compounds into steroids. The key enzymes in the early steps of the isoprenoid... 

Since the predatory water beetles cannot biosynthesise the steroid skeleton de novo, steroidal precursors must be obtained from exogenous sources. Bacillus-strains, isolated from the foregut of the water beetle Agabus affinis, were tested for their ability to transform steroids [101]. After incubation with androst-4-en-3,17-dione two Bacillus strains produced 13 different transformation products. Hydroxylation took place at C6, C7, Cll and C14 resulting in the formation of 6fi-, 7a-, 1 la-, and 14a-hydroxyandrost-4-en-3,17-diones. After incubation with pregnenolone the two Bacillus strains produced a variety of steroids among which 7a-hydroxypregnenolone was the major product [102]. 

Further examples of the importance of functional groups for behavior are the responses of simfish to steroids in beetles, their prey reactions of birds and mammals to capsaicin-related compounds and fear behavior of rats when exposed to sulfur compoimds from fox urine and feces. 

Of several related steroids in the defensive secretion of dytiscid beetles, deoxycorticosterone was most effective. It deterred simfish from feeding in 94% of the tests. Other steroids (pregnolones) that differed only by lacking a keto group at one carbon atom were either intermediate or not active at all (Gerhart etal., 1991). 

Gerhart, D. J., Bondura, M. E., and Commito, J. A. (1991). Inhibition of sunfish feeding by defensive steroids from aquatic beetles structure-activity relationships. Journal of Chemical Ecology 17,1363-1370. 

The potato beetle (Leptinotarsa decemlineata) lives on Solanum species containing steroid alkaloids, which are tolerated, but not stored, by this species. The bruchid beetle Callosobruchus fasciatus predates... 

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]. 

Several arthropods are rich sources of steroidal defensive compounds. These progestagens are particularly common in water beetles of the subfamilies Colymbetinae and Dytisci-nae. Beetles of these families accumulate steroidal toxins as... 

Many steroidal alkaloids are repellent or antifeedant to insects. This may be attributable largely to the membrane destabilizing effects of the alkaloids (Roddick et al., 1988). Demissidine (76), solacauline (75), soladulcine (74), sola-nine (71), and tomatidine (52) are phagorepellent to Leptinotarsa decimlineata (Colorado potato beetle). a-Chaconine (72), solanidine (49), solanine (71), and tomatidine (52) are feeding deterrents to Choristoneura (Wink, 1993). 

As mentioned above, demissine and several other steroid alkaloids are repellent or toxic to the Colorado potato beetle. Races of this insect are adapted to several Solanum species, including S. eleagnifolium, S. rostratum, and 5. tuberosum, and the insect has a recognized ability to adapt to new combinations of steroid alkaloids (Harbome, 1986). 

Barbour, J. D. and G. G. Kennedy, Role of steroidal glycoalkaloid a-tomatine in host-plant resistance of tomato to Colorado potato beetle, J. Chem. Ecol., 17, 989-1005 (1991). 

---