Antifeedant assays

It is difficult to compare these results with those given in the literature for other substances using different testing procedures [77]. However, the use of triphenyl tin acetate has previously been studied under similar conditions to those described herein with a FRso=0.37 when the assay dose was 10 pg/cm2 [18, 81]. Therefore, more than eight of the new products in principle appear to be more active than triphenyl tin acetate, which is the standard for antifeedant assays. 

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. 

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. 

The difficulty in relating resistance gene frequencies, the presence of resistant phenotypes and the level of resistance to field control indicates a need for monitoring techniques that sample significant numbers of a population and more accurately reflect the field situation (23-24). For example, in many cases, the standard topical assay may not adequately reflect the situation in the field. The efficacy of the pyrethroids seems to depend on many factors other than just contact activity. In cases where topical assays indicate high levels of resistance but no corresponding field failures, contact activity may not be the only factor affecting susceptibility. The repellency and antifeedant attributes of the pyrethroids may also contribute to their efficacy in the field (25-31). These behavioral attributes may also affect the evolution of resistance in field populations (22). The type of exposure in the field to the pyrethroids may also affect field control more than previously considered (33). 

Wilfordin, tryptofordin and celangulin (Fig. 14) are antifeedant compounds obtained from extracts of the Celastraceae species Maytenus rigida [78], Trypterigium wilfordii [79] and Celastrus angulatus [77, 80], respectively, and as some products isolated from South American species have similar structural characteristics, they too have been assayed. 

The insects used for assay were fifth-instar larvae of Spodoptera littoralis Boisduval (Lepidoptera, Noctuidae) and the methodology used to determined the FR50 was that described in references [18, 81]. Antifeedant activity has been discerned in 16 sesquiterpenes obtained from five endemic Latin American species. The results are set out in Table XXII. All compounds were active at a dosage of 10pg/cm2 with 72 the most active with FRso<0.5 at a dose of 0.1 pg/cm2. 

Products isolated from plants of the Celastraceae family have showed insecticidal and antifeedant activities, as discussed earlier. The compounds reported belong to the agarofuran sesquiterpene-type and sesquiterpene pyridine-type alkaloids. Nevertheless, the only description of insecticidal activity of quinone methides found is from Avilla et al [102], Despite the fact that the compounds assayed were known the... 

The three metabolites assayed produced the same effect on the insect used that the control (a commercial extract of the neem tree, containing 2% of azadirachtin), although at higher concentrations. 20a-hydroxy-tingenone was the most active compound among the three assayed. Pristimerin shows also a high antifeedant activity together with molt effect suppression. 

Compounds showed weak activity in both assays, due to their hemiacetal structure. In general, all compounds showed potent antifeedant and insecticidal activity at concentrations of 16.0-63.7 pg/cm2. These compounds contained the following partial structures an a,P-unsaturated carbonyl in ring A, vicinal hydroxy groups at Cn and Ci2, a methyleneoxy bridge between Cg and C13 and a side chain atCis [111]. 

The most potent compounds were further tested at a lower concentration of 1.0-4.0 pg/cm2. These results can be summarized as follows a) the aglycone, isobrucein-B (235), showed the highest potency in both assays. The antifeedant activity may result in its... 

From the Caribbean sponge Cacospongia linteiformis was isolated lintenone (156) with a new tricarbocyclic skeleton, which contains fused cyclohexane, cyclopentane and cyclobutane rings. Lintenone exhibited high antifeedant activity against the fish C. aurantus (30 pg per cm2 of food pellets), ichthyotoxicity to G. affinis (10 ppm) and moderate toxicity in A. salina assay (LC50 109 ppm) [166]. 

Table 2. Average antifeedant effect (%FI) + standard error, and effective antifeedant doses (EC50) of the test compounds against S. littoralis sixth-instar (L6) larvae and L. decemlineata adults in choice assays [17].

We proceeded with the bioassay-directed chemical study of this plant. From the active fractions we isolated bisabolene- and silphinene-type sesquiterpenes (23 and 24). These compounds are strong CPB antifeedants in both choice and no-choice assays, the adult insects being the most sensitive to their action (table 6) [32], Their antifeedant potencies were similar (23) or stronger than that of limonin (24), a CPB antifeedant triterpene [33],... 

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