The pyrethrins and related compounds. Part XXVIII: Alkenyl- and alkynyl-substituted benzyl esters

Over 100 benzyl esters of pyrethroidal acids were synthesised and tested for insecticidal activity to establish detailed structure–activity relationships in compounds with side-chains similar to those in the natural pyrethrins. Alkenyl, and corresponding alkynyl, side-chains were effective, both at the 3- and 4-positions, as were side-chains with extended substitution in either E or Z forms. A cyano group at the α-position increases activity if the side-chain is at C-3, but lowers it drastically if the substituent is at C-4. Similarly, methyl groups at C-2 and/or C-6 may increase activity whether the unsaturated side-chain is at C-3 or C-4, but only in the absence of an α-cyano group.     

Llaves,voitures, and tope [keys (sp.), cars (fr.), and mud (Swahili)] — the real reasons behind success or failure of field crop protection projects

Crop protection research in the Tropics is always interesting and challenging, and usually professionally rewarding. Once involved, researchers often find it difficult to leave international research settings. However, the wise field scientist, when choosing such a career, will make Barley ’s (3) “The Innocent Anthropologist ” required reading and purchase a very good pair of binoculars and a local bird guide. Even the most resourceful individual is going to have a considerable amount of time to add birds to one ’s life list, improve species distribution maps, or possibly even identify a new species while waiting for the key to be found, the vehicle to show up, or the mud to dry out.     

A PCR diagnostic for cyclodiene insecticide resistance in the red flour beetle Tribolium castaneum

A molecular diagnostic was used to examine the conservation of cyclodiene resistance associated mutations between different strains of Tribolium castaneum (Herbst.). An improved insecticide bioassay for discrimination between resistant genotypes was developed and seven resistant strains were established from five different continents. In order to develop a molecular diagnostic a partial cDNA of the cyclodiene insecticide resistance gene Rdl, a γ-aminobutyric-acid-gated chloride-ion channel, was cloned and sequenced. This cDNA spans exon 7, the region containing the resistance-associated mutation, and part of exon 8. An ‘allele-specific’ oligonucleotide primer, carrying the resistance-associated mutation at its 3′ end, was used in combination with a flanking ‘allele-independent’ primer in the polymerase chain reaction to selectively amplify a single resistance-associated mutation from all seven strains collected worldwide. The implications of these findings for the population genetics of insecticide resistance and its management in pest insects via quarantine are discussed.     

Patterns of Variation in Alkamides and Cichoric Acid in Roots and Aboveground Parts of Echinacea purpurea (L.) Moench

We investigated patterns of variation in alkamides and cichoric acid accumulation in the roots and aboveground parts of Echinacea purpurea (L.) Moench. These phytochemicals were extracted from fresh plant parts with 60% ethanol and quantified by high performance liquid chromatography (HPLC) analysis. Concentrations of alkamides and cichoric acid were measured on a dry-weight basis (mg·g(-1)). For total alkamides, concentrations among individual plants varied from 5.02 to 27.67 (mean = 14.4%) in roots, from 0.62 to 3.42 (mean = 1.54) in nearly matured seed heads (NMSH), and 0.22 to 5.25 (mean = 0.77) in young tops (about ? flower heads, ? leaves, and ? stems). For cichoric acid, concentrations among individual plants varied from 2.65 to 37.52 (mean = 8.95), from 2.03 to 31.58 (mean = 10.9), and from 4.79 to 38.55 (mean = 18.88) in the roots, the NMSH, and the tops, respectively. Dodeca-2E, 4E, 8Z, 10E-tetraenoic acid isobutylamide and dodeca-2E, 4E, 8Z, 10Z-tetraenoic acid isobutylamide (alkamides 8/9) accounted for only 9.4% of the total alkamides in roots, but comprised 87.9% in the NMSH, and 76.6% in the young tops. Correlations of concentrations of alkamides or cichoric acid between those of roots and those of the NMSH were not statistically significant, and either within the roots, the NMSH, and the young tops. However, a significant negative correlation was observed between the concentration of cichoric acid in the roots and in young tops, and a significant positive correlation was observed between total alkamide concentration in the roots and cichoric acid concentration in the young tops. These results may be useful in the genetic improvement of E. purpurea for medicinal use.     

Nerve insensitivity resistance to cypermethrin in larvae of the tobacco budworm Heliothis virescens from USA cotton field populations

Spontaneous neuronal activity was recorded from the peripheral nerves of third-instar larvae of strains of Heliothis virescens (F.) obtained directly from cotton fields in the USA. Following a control period the preparations were exposed to increasing concentrations of cis-cypermethrin in a cumulative dose-response assay. A positive response was defined as an increase of at least five-fold in the rate of neuronal activity over that seen during the control period. Up to 35 individuals of each strain were assayed and the responses used to construct a phenotypic profile categorising the individuals from nerve-susceptible to highly nerve-insensitive. An EC₅₀ for the action of cis-cypermethrin was also obtained. There was a positive, significant correlation between non-synergisable resistance to cypermethrin and nerve insensitivity as defined in the neurophysiological assay. It was shown that nerve insensitivity to cypermethrin increased throughout the cotton-growing season.     

Evaluation of cinnamamide as an avian repellent: Determination of a dose—response curve

The dose-response curve was quantified for the avian repellency of cinnamamide, a derivative of the plant secondary compound cinnamic acid, using a three-day, ‘short-term no-choice’ test. This test was designed to resemble more closely the availability of alternative food in the birds' natural environment than in previous no-choice studies. Cinnamamide reduced food consumption by feral pigeons (Columba livia Gmelin) at concentrations as low as 6.17 μmole g^?1 food (0.09% w/w) and this reduction increased with concentration. An R₅₀ index, the concentration at which food consumption was reduced by 50% was interpolated from the dose-response curve as 18.4 (±0.38) μmole g^?1 food 10.26% w/w). This index can now be matched with those of related compounds in future structure-activity studies. The birds' response to cinnamamide changed over the three-day trial with respect to concentration. Repellency declined at concentrations < R₅₀ and increased at concentrations > R₅₀. This suggests that pigeons become habituated to cinnamamide at low concentrations but at high concentrations they may develop a conditioned aversion. This study provides quantitative confirmation of previous laboratory and field demonstrations of cinnamamide's effectiveness as a non-lethal chemical repellent suitable for reducing avian pest damage.     

Structure and general properties of mineral and vegetable oils used as spray adjuvants

The abiogenic and biosynthetic origins of mineral and vegetable oils are contrasted and the importance of soybean, palm, rape seed and sunflower as the major source of fatty acids is highlighted. The cheaper oils derived from animal sources also provide fatty acids. The extraction and refining processes for vegetable oils are explained, the composition of typical vegetable oils is discussed and the importance of the glyceride structure to the physical properties of the oils is emphasised. Stability, volatility and viscosity of vegetable oils are considered. Production of fatty acids by fat-splitting methods and the formation of methyl esters by inter-esterification are outlined. Mineral oil compositions are detailed and their properties explained.