Citrus insects, pheromones

As in the case of the Comstock and citrus mealybug pheromones, the release data for the California red scale pheomone showed that the laminate formulation made with 16-mil polymeric PVC film gave a long-lasting and suitable dispenser for the monitoring program. The results of these dispenser evaluations are summarized for citrus insect pheromones in Table IV. 

In 1980, we reported the structure of the Comstock mealybug, Pseudococcus comstocki (Kuwana), pheromone as 2,6-dimethyl-l,5-heptadien-3-ol acetate (24, 25) and in 1981, we identified the pheromone of the citrus mealybug, Planococcus citri (Risso), as (lR-cis)-(+)-2,2-dimethyl-3-(l-methylethenyl)cyclobutanemethanol acetate (26). Both of these pheromones have been synthesized and are currently being used as baits in monitor traps in California and Texas. These compounds are more volatile than the pheromones for most other insects and therefore formulations for controlled release need to be modified from those described earlier. 

Non-cyclic sesquiterpenes include the volatiles a- and (3-farnesene (which have alarm pheromone activity) and pleasant odorants from Citrus sinsensis (orange) (Rutaceae), namely a- and [i-sinensal (mandarin peel odour) and nerolidol from orange flower oil (oil of neroli). The epoxide JH III is produced by Cyperus iria (Cyperaceae) and acts critically on insect development. 

The spined citrus bug (Biprorulus bibax) is a pest of citrus in southern Australia. The major component (74, Figure 4.5) of the male-produced pheromone of B. bibax was isolated and identified by the joint work of James in Australia and Oliver et al. in the USA. Oliver found by chiral GC analysis that the insect produces a single enantiomer of 74. In 1992 I became interested in clarifying the absolute configuration of this pheromone, because Dr. Oliver requested me to do so. 

The majority of insect and mammalian pheromones are small and relatively simple molecules with low polarity. Nonpolar polysiloxane phases such as 100% polysiloxane or 5% polyphenylmethyl siloxane are the preferred column for pheromone research due to a broad range, thermal stability, and long lifetime. Five per cent (phenyl)methylpolysiloxane columns were used in the identification of dodecenyl acetate and dodecenol, the sex pheromones of the citrus fruit borer, and anisole, the sex pheromone of the scarab beetle. A 100% polysiloxane column was used in the analysis of dodecenyl acetate, the female sex pheromone of the Asian elephant. 

Sesquiterpenic alcohols Examples of sesquiterpenic alicyclic alcohols (8-24) are farnesol and nerolidol (also known as peruviol). Both alcohols, smelling of flowers, are components of many essential oils used in perfumery. Of the four possible geometric isomers, the (2 ,6B)-isomer of farnesol, is the most common in nature and occurs, for example, in basil oil and ambrette (Abelmoschus moschatus Malvaceae) seed oil. The (2Z,6 )-isomer occurs in the petit grain oil bigarade, which is derived from the bitter orange tree leaves (Citrus aurantiumvai. amara, Rutaceae). Farnesol is a natural pesticide for mites and a pheromone for several species of insects. Nerolidol with a double bond at C-6 occurs in the form of (Z)- and ( )-isomers, each of which can exist as an enantiomeric pair (chiral carbon C-3). The individual enantiomers and their mixtures are found in many essential oils. For example, the essential oil known as cabreuva oil that is used in perfumery is obtained from the bark of the South American tree Myrocarpus frondosus (Fabaceae) and contains the (-F)-(E)-isomer of nerolidol (3S,6 )-nerolidol. 

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