Adults of many species of Lepidoptera, principally the males, frequent mud puddles, edges of streams, carrion and animal excreta where they imbibe moisture, an activity referred to as 'puddling'. Sodium ions are the only known stimulus present which cause males of at least two lepidopteran species to drink for extended periods. In the European skipper Thymelicus lineola (Ochsenheimer) (Lepidoptera: Hesperiidae), only males puddle, even though they have concentrations of abdominal sodium 2-3 times that of females at emergence. During their first mating, males transfer 32% of their abdominal sodium to females. This could be of considerable importance given that an average egg complement contains >SO% of the total body sodium of females at emergence. Virgin females. as well as having reduced fecundity, have reduced longevity. This is attributed to virgins not obtaining important nutrients which males transfer to females during mating. Access to sodium ions increases the total number of matings by c . 50% for males living >1S days. Access to sodium ions by once-mated males increases the percentage of males which re-mate on the day following first mating; the percentage of females, mated to the twice-mated males, which lay >SO% fertile eggs; and the drought resistance of eggs laid by those females.
Plant chemicals in three cruciferous crop species, Brassica napus L., B. juncea (L.) Czerniak, and Sinapis alba L., that stimulate oviposition in the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae) were investigated in laboratory bioassays. Aerial portions of 4-to 6-week-old plants were extracted and fractionated using ion-exchange liquid chromatography. The oviposition stimulants were identified as glucosinolates, which are found in all Brassicaceae species. Activity of extracts was largely eliminated by treatment with myrosinase or sulphatase, enzymes which degrade glucosinolates. Reference standards of the same glucosinolates and in the same concentrations as in the extracts were equally stimulatory. A test with eight different glucosinolates demonstrated that the moths do not discriminate between glucosinolates with different side-chain structures. However, in tests using allylglucosinolate the oviposition response was dose-dependent. One of the species tested, S. alba, contained a possible oviposition deterrent.
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