No abstract

The clearwinged grasshopper, Camnula pellucida, exploits incident solar radiation to raise internal body temperatures above ambient levels. Under adequate temperature and light conditions, grasshopper body temperatures may exceed air temperatures by 10°—15°C with both nymphs and adults preferring to thermoregulate near 40°C, their optimal temperature for development. Comparison of age—specific phenology data collected from field sites with projections from computer simulation studies on grasshopper development, indicated that incident solar radiation can highly accelerate maturation of grasshoppers. Also, prolonged exposure to temperatures above 35°C is beneficialto grasshoppers, as it is detrimental to the fungal pathogen Entomophaga grylli (US pathotype I), which is a major cause of natural mortality in many species. E. grylli protoplasts grew little or not at all if incubated at a constant 35°C in tissue culture medium. Studies, conducted in vivo at constant temperatures, verified that E. grylli has an upper thermal limit of survival and development near 35°C. IN nature, however, these organisms are exposed to fluctuating temperatures. Further in vitro studies revealed that protoplast survival and development were significantly affected by incubation at 40°C for as little as 2 h per day and almost totally inhibited by 40°C for 8 h each day. In vivo incubation studies also showed an increase in the incubation period and a decline in the proportion of grasshoppers dying of E. grylli mycosis with increased daily exposure to 40°C. Infected grasshoppers were also held at 25°—30°C and allowed to range freely between shaded and lighted areas, so body temperatures could be raised through normal basking activity. Compared to a control group held in diffuse light, E. grylli mycosis was almost totally eliminated from the basking grasshoppers. The few individuals treated with solar radiation that died from E. grylli infection survived significantly longer then infected individuals not exposed to the solar simulator. Computer simulations using field—collected temperature, moisture, and solar radiation data revealed that behaviorally regulated thermal effects on E. grylli survival and development could limit disease development in some locations and seasons. Although it is unclear that the behavioral trait of basking is an adaptive response to selection pressures caused either by the pathogen or by other selective factors, it is clear that thermoregulatory behavior provides survival advantages to C. pellucida. In addition to their specific biological significance, these results demonstrate that behavioral exploitation of a physical resource in the environment can be used to profoundly alter biological relationships between species in this case, allowing one organism to eliminate an antagonist by causing its mortality.

Four species of saltcedars, Tamarix ramosissima Ledeb., Tamarix chinensis Lour., Tamarix parviflora DC., and T. canariensis Willd. and their hybrids, are exotic, invasive small trees from Asia that cause great damage to riparian ecosystems of the western United States. They displace native plant communities, degrade wildlife habitat (including that of many endangered species), increase soil salinity and wildfires, lower water tables, reduce water available for agriculture and municipalities, and reduce recreational use of affected areas. Phytophagous insects are abundant on saltcedar in the Old World and we selected Diorhabda elongata Brull e e deserticola Chen as the top candidate biological control agent because of the great damage it causes, and its high host specificity, broad geographic range, and presumed adaptability in the United States. Literature review and our overseas surveys indicated that this insect is associated only with species of Tamarix and occasionally with Myricaria but not with Reumaria or Frankenia (all Tamaricales) in the Old World. In quarantine facilities in the United States, and overseas, we tested beetles from China and Kazakhstan on six species and three hybrids (26 accessions) of Tamarix and on 58 species of other plants, in 15 tests of different types, using 1852 adults and 3547 larvae, over 10 years. Survival from larvae to adults averaged 55-67% on the Tamarix species, 12% on Myricaria sp., and only 1.6% on the three Frankenia spp. No larvae completed their development on any of the other 54 plant species tested, where most larvae died during the first instar. Adults oviposited readily on T. ramosissima accessions, less on Tamarix aphylla (L.) Karst. (athel), and only rarely on other plants. The host range of the D. e. deserticola we tested from Kazakhstan was not different from those we tested from China. Therefore, D. e. deserticola, is sufficiently host-specific and was approved for field release in North America. This is the first biological control agent introduced into the United States for control of saltcedar. Published by Elsevier Science (USA).

The biology, ecology, disease etiology, and biological control potential of different members of the Entomophaga grylli species complex are discussed. This complex is represented by several pathotypes that include members that produce both conidia and resting spores within a single season, and members that produce only resting spores. This complex is known as a major pathogen of acridids from most areas of the world where populations of these insects are found, including Africa, Asia, Australia, Europe, North America, and South America. Pathogens from this species complex commonly cause disease epizootics in their host populations and are known to reduce significantly outbreaks of grasshoppers, particularly following periods of rain or high humidity. Specific factors that either limit or enhance disease processes and host mortality are discussed in relation to both epizootiology and biological control programmes. Recent biological control efforts are discussed and the potential of using members of the E. grylli species complex in both augmentation and introduction programmes is considered.