Tetsuo Saito

Sterols in Laodelphax striatellus with special reference to the intracellular yeastlike symbiotes as a sterol source

Abstract Sterols were analysed to investigate the sterol source in Laodelphax striatellus and three other rice plant-sucking homopterous insects. In L. striatellus, cholesterol, 24-methylenecholesterol and β-sitosterol were detected. The host plant (rice) contained campesterol, stigmasterol and β-sitosterol. From the honeydew excreted by L. striatellus, cholesterol, β-sitosterol and negligible amounts of campesterol were recovered. Laodelphax striatellus possesses yeastlike symbiotes which can be destroyed by high temperature. Fifth instar nymphs, which have been exposed to 35°C for 3 days in their 1 st instar, showed lower cholesterol concentration and markedly reduced amounts of 24-methylenecholesterol. From the results it is concluded that L. striatellus has two sterol sources: one from the host plant and the other from the yeastlike symbiotes which appear to provide 24-methylenecholesterol.

Electroantennogram and behavioural responses of the gypsy moth to enantiomers of disparlure and its trans analogues

Abstract The attractive power of both enantiomers of disparlure and its trans analog was tested electrophysiologically (electroantennogram = EAG) and behaviourally (whole organism response). EAG responses correlated very well with the behaviourally determined effectiveness sequence: cis(+)-disparlure was the most effective substance; the authentic racemic disparlure came second; cis(−)-disparlure inhibited the activity of cis(+)-disparlure; and trans enantiomers were not significantly different from the control. These results allow us to conclude that cis(+)-disparlure is the natural sex pheromone of the gypsy moth, and that the male antennae have a chiral receptor system in the antenna for the reception of the sex pheromone.

Selective toxicity of systemic insecticides

Systemic action of plant tissues may offer a possibility of developing ecological selectivity: once the insecticide is absorbed and translocated in the plant tissues, only phytophagous pests will consume it directly, and it reduces the population of plant-feeding pests without killing beneficial organisms. Therefore, systemic activity is a very desirable property of both insecticides and fungicides. The usage of systemic compounds may decrease the spray coverage, making possible the use of lighter application equipment, and decrease the cost of application. Also, pests whose habitats prevent intoxication by contact insecticide, e.g., apple leaf curling aphid, Myzus malisuctus Matsumura, may be controlled by the systemic insecticide.