Graduate Thesis Or Dissertation

The effects of synthetic juvenile hormone on the leafhopper, Draeculacephala crassicornis

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  • The effects of synthetic juvenile hormone on the viability of eggs, metamorphosis of nymphs, and mating behavior of males and females in diapause was investigated by treating Draeculacephala crassicornis with ENT 33972a. The viability of eggs was reduced 14% by a small dose (0.001 μg) of synthetic juvenile hormone applied topically to the eggs; however 8% of the eggs were still viable after they had been treated with 2.0 μg of hormone. The age of the eggs did not affect their sensitivity to the hormone. Third, IV, and V instars responded differently to topical treatments of synthetic juvenile hormone. A 5.0 μg dosage of hormone was more lethal to III instars than IV and V instars, but a larger dosage of hormone was required to produce morphological abnormalities in III instars than in older nymphs. The adult emergence of most IV instars was prevented by a hormone dosage of 0. 50 μg Morphological abnormalities were produced when young V instars (less than 3 days) were treated with hormone but older V instars (greater than 8 days) molted to normal adults even when they were treated with large dosages of hormone. Hormone treatment of V instar females committed to enter diapause prevented the reproductive diapause of the subsequent adults, but treatment of older V instar females committed to develop ovaries had no effect on subsequent adult egg production and offspring survival. The viability of eggs from gravid females which were treated topically with only 0.001 μg of hormone was reduced by 22%, but larger dosages (up to 5.0 μg) had little additional effect. In this study, the hormone produced no deferred effects on offspring from viable eggs. Females in diapause were topically treated with a small dose (1.0 μg)of synthetic juvenile hormone to observe the effect of the hormone on survival and ovarial development. The survival of the females was not markedly affected and these females developed and oviposited a normal complement of eggs in autumn. The activity of foliage sprays of seven synthetic juvenile hormones was compared. Three of these compounds, ENT 33972a, ENT 70119a, and ENT 70221 prevented the adult development of IV instars, and also terminated the reproductive diapause of females. The compounds were active against IV instars and females at the respective spray concentrations of 0.10 and 1.0%. Comparable results were obtained in laboratory and field tests. Laboratory tests were designed to study the effects of synthetic juvenile hormone on the mating activity of males and females in diapause. Females in diapause had undeveloped ovaries and were not attractive to males. When these females were treated with synthetic juvenile hormone, they mated after they had initiated ovarial development. Males in diapause did not mate readily unless they had been treated with synthetic juvenile hormone. Additional laboratory experiments showed that the hormone stimulated the mating behavior of males in diapause but had no effect on the growth of testes or the rate of increase of mature sperm bundles in the testes. However, mature sperm bundles appeared earlier in the testes of treated than untreated males. Periodic sampling of a field population of males in diapause revealed that their low mating activity was not due to underdevelopment of the testes since the testes matured at the same rate as those of nondiapausing males in the field. Laboratory studies of males in diapause which were confined in controlled environments showed that their mating activity was stimulated by short days but not affected by temperature.
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