Heather S. Costa

Cultural practices for managing Bemisia tabaci and associated viral diseases

Abstract Whiteflies ( Bemisia spp.) and the viruses they vector cause extensive losses to many horticultural and agronomic crops throughout the tropics and subtropics. These losses have spurred a worldwide search for cost-effective management strategies. Cultural practices can play a significant role in integrated pest management (IPM) systems targeting whiteflies, because of their preventative nature. Yet, cultural practices have received disproportionately little attention from researchers, possibly due to the difficulty of testing by conventional methods. Practices such as crop-free periods, altering planting dates, crop rotation, and weed and crop residue disposal, perform well only if used on a regional scale and therefore are difficult to test or demonstrate experimentally. Growers may also be reluctant to adopt cultural practices such as living barriers, high planting densities, floating row covers, mulches, and trap crops, that require significant changes in conventional cropping practices. Nonetheless, we have seen adoption in recent years of some cultural practices to manage whiteflies, such as crop planning that includes host-free periods, and various forms of screened exclusion. This review focuses on research efforts, field utilization, and the potential of cultural practices to manage the whiteflies and associated viral diseases.

Seasonal flight activity of two Homalodisca species (Homoptera: Cicadellidae) that spread Xylella fastidiosa in southern California.

Abstract Homalodisca coagulata (Say) and Homalodisca lacerta (Fowler) are vectors of a new bacterial disease of oleander in California known as oleander leaf scorch, induced by the bacterium Xylella fastidiosa. H. coagulata also has been implicated in the spread of the strain of X. fastidiosa that induces Pierce’s disease of grapevines in California. We monitored the flight activity of H. coagulata and H. lacerta in oleander and citrus by using yellow sticky cards at three southern California locations where outbreaks of oleander leaf scorch have been documented, and where vector compliments are different. Areas sampled included a mesic coastal area (Irvine, CA) that supports predominantly H. coagulata and few H. lacerta, a dry inland location (Palm Desert, CA) that supports predominantly H. lacerta and few H. coagulata, and an intermediate area (Riverside, CA) supporting both Homalodisca species. From November 1996 to October 1999 peak catches of both Homalodisca species occurred during the midsummer at all locations. H. coagulata was trapped in greater numbers in citrus than in oleander at both the Riverside and the Irvine sites. Likewise, H. lacerta in Riverside was more associated with citrus than oleander, yet H. lacerta in Palm Desert was trapped in greater numbers in oleander than citrus.

Pre-Imaginal Egg Maturation and Bacteriocyte Inclusion in Bemisia aff. gigantea (Hemiptera: Aleyrodidae)

Abstract In this study, we investigated patterns of egg production and inclusion of bacterial endosymbionts in the whitefly Bemisia aff. gigantea Martin, a species native to lowland tropical rain forests of North Queensland, Australia. Development of the female reproductive system of B. aff. gigantea becomes evident in fourth instar/pharate adults, with extensive accumulation of mature (chorionated) eggs occurring 1–2 d before adult eclosion. Evidence from light and electron microscopy indicates that bacteriocytes (specialized cells containing bacterial endosymbionts) appear scattered through the abdominal region in close association with the developing eggs. In pharate adults, bacteriocytes seem to enter developing eggs basally through the pedicel, and after oviposition they move distally from the pedicel as the embryo matures. In addition, developing ova without bacteriocytes were evident in 3-d-old females, indicating that oogenesis and bacteriocyte inclusion is an ongoing process.