Antifeedant bioassay

Scutalpin B (142) was isolated from Scutellaria alpina subsp. lambrensis (Lamiaceae) together with scutalpin C (143). In choice antifeedant bioassays against S. littoralis, 143 was only slightly less active than jodrellin B (112) (97% versus 100%). Acetylation of the 11/3-hydroxyl group of 143 resulted in the formation of 142 and caused a significant decrease in antifeedant activity (from 97 to 27% inhibition).78... 

The results of the boll weevil antifeedant bioassays with anthrani-lic acid, gentisic acid, senecioic acid, cinnamaldehyde and cinnamic acid are presented in Table II. Camphor was not bio-assayed due to its extreme volatility. However camphor is a known moth repellent (8) and is probably a boll weevil antifeedant since the fraction from which it was isolated was active. 

Tliis study describes the isolation and bioassay against insects of six compounds from the Peruvian plant Alchornea trlplinervia. The compounds anthranilic acid, cinnamic acid, and camphor showed significant inhibition of the growth of the tobacco budworm. Anthranilic acid, gentisic acid, senecioic acid, cinnamic acid, and cinnamaldehyde demonstrated low to moderate activity in the boll weevil antifeedant bioassay. Cinnamaldehyde, a constituent of the spice cinnamon, showed the highest level of inhibition to boll weevil feeding. 

Leafedisk Antifeedant Bioassay Ten l.O cm sweet potato leaf disks were placed in marked wells in an agar-coated petri dish. Five disks were alternatively treated with 10 pi of plant extract (100 pg/cm ) or solvent (acetone or methanol). Five third instar Spodoptera litura (Lepidoptera Noctuidae) larvae per dish and three dishes were used per treatment. The treated dishes were placed in an incubator at 27 C and 75-80% RH for 16-18 hours in darkness. The leaf surface consumed was measured with a video camera interfaced to a personal computer as described earlier (6). The feeding index was calculated as 1= %T / (%T + %C) (%T = % of treated disks consumed, %C = % of control disks consumed). An arbitrary level of I<20 was used as the criteria to determine effective feeding deterrents (7). 

Other studies show the presence of a diversity of compounds other than limonoids as defenses in the tissues of Meliaceae. Woody tissues of Trichilia trifolia afforded three novel dolabellanes with flexible Curing structures. These substances were very active antifeedants in the Sitophilus bioassay (Ramirez et al., 2000). T. martiana seeds yielded large amounts of 2-((Z,Z)-6,9-heptadecadienyl)furan. T. hirta and T. americana bark have yielded novel steroids by insect bioassay-guided isolation and application of a nanoprobe nuclear magnetic resonance (NMR) technique for structure elucidation (Chaurest etal.,1996). Compounds isolated included hydroxyandrosta-l,4-diene-3,16-dione (Fig. 1.4) and derivatives. However, studies by Wheeler et al. (2001) suggest that other unidentified compounds may also be... 

Important aspects bioassays as well as their types are discussed below. One of the main drawbacks with the bioassays is that some of them have long durations, which can delay the results. Hence, researches on new and faster bioassays are carried out. An interesting new possible bioassay involves the use of olfactory j3-waves that is, bursts of c.20 Hz fast waves that are elicited in the olfactory bulb and pyriform cortex in rats are observed.13 These fast waves are also observed in voles.14 These studies indicate that these /3-waves may provide an easy means of identifying new antifeedants in small herbivores. 

These are two different bioassays, each revealing different information. In a choice experiment, the insects are given the option to choose between two different treatments, either the control or the extract (or pure compound), or between two different compounds. Information obtained via this type of bioassay shows that one of the treatments is preferred to the other. Or in case of the difference between control and compound, that if the control is preferred, the compound could be an antifeedant. 

In a no-choice bioassay, the insect cannot choose from different treatments. Only one treatment is given. A strong antifeedant will result in no consumption of the treatment, whereas a weak antifeedant will lead to some consumption of the treatment, as the insect needs to gain nutrition. 

Both these methods have their advantages and disadvantages. To compensate for this difference in choice and no-choice bioassays, the activity of compounds are expressed by three coefficients, namely, the absolute coefficient of deterrence (A) determined by the no-choice test, the relative coefficient of deterrence (R) determined via the choice test, and the total coefficient of deterrence (T), which is calculated by combining A and R.15 16 Values of A and R are from 0 to 100. The maximum total coefficient is therefore 200. Strong antifeedants had values of 151-200. 

Treatment of potato leaf disks with 10 -clerodanes isolated from Teucrium and with 10 of their synthetic derivatives resulted in a significant antifeedant activity against L. decemlineata, although in choice and no-choice bioassay concentrations of 1000 ppm were used. For the most active compounds, effective concentration to inhibit 50% of the feeding (EC50) ranged from 53 to 394 ppm.75 Of the 12 most active antifeedants 128-139,... 

The plant material was extracted according to the procedure in Figure 1. The ethanol extract [2] (Figure 1) exhibited total inhibition of feeding against the cotton boll weevil at levels of 10, 25, and 50 mg (Table I). Further fractionation of the ethanol extract [2] showed no abatement of this antifeedant activity in either the CHClj [3] or the aqueous fraction [4] with %T/C values of less than 12% at the 10-50 mg dose levels as indicated in Table I. Further fractionation (Figure 1) and bioassay (Table I) showed that the methanol fraction [6], and the CHC /ethanol fraction [7] demonstrated excellent antifeedant activity. 

Moreover, the observation of an interesting antibiotic activity for some Lactarius extracts (3) stimulated the search of new biologically active compounds among those isolated from these mushrooms. In fact, simple bioassays (4) led to the identification of new products with antimicrobial, cytotoxic, antifeedant and other interesting activities. No less important was the observation that some species seem to withstand attack from parasites such as snails and insects better than others. In fact, it has been shown that resistant species are armed with a chemical defence system which protects the mushrooms from predators and invaders. 

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