Photoperiodic control of reproduction in the milkweed leaf beetle, Labidomera clivicollis

ABSTRACT. Photoperiod significantly affected reproduction in a central Texas population of the milkweed leaf beetle Labidomera clivicollis (Kirby) (Chrysomelidae). Laboratory reared beetles responded to a critical photoperiod of LD 12.5: 11.5; longer photoperiods induced reproduction, while shorter photoperiods induced diapause. Both larval and adult stages exhibited sensitivity to photoperiod. Beetles exposed to long days as adults reproduced regardless of photoperiod experienced as larvae. However, exposure to long days, as larvae but short days as adults also induced reproduction in an intermediate portion of the population. No larval instar appeared to be more sensitive than the others, and the proportion of the population responding did not increase with cumulative larval exposure to long days. Larval sensitivity to photoperiod may be ecologically significant to central Texas populations because it permits a substantial portion of the autumn generation to initiate a third generation in favourable years.     

Loss of genetic diversity in the North American mayfly Ephemerella invaria associated with deforestation of headwater streams

1. Terrestrial dispersal by aquatic insects increases population connectivity in some stream species by allowing individuals to move outside the structure of the stream network. In addition, individual survival and reproductive success (as well as dispersal) are tightly linked to the quality of the terrestrial habitat. 2. In historically forested catchments, deforestation and altered land use have the potential to interfere with mayfly dispersal or mating behaviours by degrading the quality of the terrestrial matrix among headwater streams. We hypothesised that loss of tree cover in first‐order catchments would be associated with an increase in population substructure and a decrease in genetic diversity of mayfly populations. 3. To test this hypothesis, we investigated spatial patterns of genetic variation in the common mayfly Ephemerella invaria across a gradient of deforestation in the central piedmont region of eastern United States. Intraspecific genetic diversity and population substructure were estimated from data obtained using fluorescent amplified fragment length polymorphism (AFLP) markers. 4. We found that mayfly populations had low population substructure within headwater stream networks and that genetic diversity was strongly negatively correlated with mean deforestation of the first‐order catchments. The large‐scale pattern of population substructure followed a pattern of isolation by distance (IBD) in which genetic differentiation increases with geographical distance, but assignment tests placed a few individuals into populations 300 km away from the collection site. 5. Our results show that loss of genetic diversity in this widespread aquatic insect species is co‐occurring with deforestation of headwater streams. 6. Most arguments supporting protection of headwater streams in the United States have centred on the role of these streams as hydrological and biogeochemical conduits to downstream waters. Our work suggests that headwater stream land use, and specifically tree cover, may have a role in the maintenance of regional genetic diversity in some common aquatic insect species.     

Relationship between Water Potential and Leaf and Inflorescence Initiation in Helianthus annuus

The total number of leaves produced by the primary stem of Helianthus annuus L. cv. Pole Star and cv. Peredovik, was reduced from 29 leaves to 21–22 leaves when water stress ranging from ?2000 to ?3000 kPa was imposed over the period from day 10 to day 20 after sowing, by withholding water from the soil. Extending the stress period by 10 days did not cause any further significant reduction in leaf number. Examination of the shoot apex showed that the leaf initiation rate was depressed by low water potential, the greatest effect occurring in the range 0 to ?1000 kPa. It was established that inflorescence initiation commenced about 18 days after planting in control plants and this was delayed by only about 4 days by low water potentials in the range ?1000 to ?3000 kPa.     

New World Thripidae (Thysanoptera) with nine-segmented antennae

A key is provided to the New World genera of Thripidae with nine-segmented antennae. Psydrothrips kewi gen. et sp. nov. is described, a discussion is given of the morphology of the Neotropical genera which it resembles, and keys to species are provided.     

Cellulase, Fruit Softening and Abscission in Red RaspberryRubus idaeusL. cv Glen Clova

The ripening of raspberry fruit (Rubus ideausL. cv Glen Clova)is associated with a climacteric rise in ethylene production.As the fruit pigments change from green to red there is a progressivesoftening, loss of skin strength and a breakdown of cell wallsin the mesocarp. An increase in cellulase (endo-1,4-ß-D-glucanase)in both drupelets and receptacles accompanies these changes.The localization of cellulase in the regions of the fruit associatedwith abscission zones suggest the enzyme may be involved infruit separation as well as softening. Rubus idaeusL; raspberry; fruit ripening; ethylene; abscission; cell wall breakdown; cellulase; endo-1,4-ß-D-glucanase