Thermal ecology of Zonocerus variegatus and its effects on biocontrol using pathogens (original) (raw)
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Ecological Entomology, 2005
1. The thermal biology of the meadow grasshopper, Chorthippus parallelus, a common, habitat generalist acridid species found in the U.K., was characterised and the influence of thermoregulatory behaviour for resistance against a temperate (Beauveria bassiana) and tropical (Metarhizium anisopliae var. acridum) fungal pathogen was determined. 2. Chorthippus parallelus was found to be an active behavioural thermoregulator, with a preferred temperature range of 32-35 C. 3. Both pathogens proved lethal to fifth instar and adult grasshoppers. No evidence of behavioural fever in response to infection by either pathogen was found, but normal thermoregulation was found to reduce virulence and spore production of B. bassiana. Normal thermoregulation did not appear to affect M. anisopliae var. acridum. 4. These results suggest that the effects of temperature on host resistance depend on the thermal sensitivity of the pathogen and, in this case, derive from direct effects of temperature on pathogen growth rather than indirect effects mediated by host immune response. 5. The implications for possible risks of exotic pathogens and influence of climate change are discussed.
Agricultural and Forest Entomology, 2007
1 Recent years have seen an upsurge in locust and grasshopper populations in many parts of the world. Environmentally sustainable approaches to locust and grasshopper control may be possible through the use of biopesticides based on entomopathogenic fungi. Unfortunately, the performance of these biopesticides is highly variable with environmental temperature and host thermoregulatory behaviour critically determining the pattern and extent of mortality after applications. Here, we present a temperature-dependent model that enables us to predict the field performance of Metarhizium anisopliae var. acridum , the key fungal pathogen used in locust biopesticides. 2 The model was constructed using mortality rate data generated across a range of temperatures in the laboratory and is driven by environmental temperature data linked through host body temperature models. 3 Model predictions were validated against empirical field data obtained for five species, Locustana pardalina , Oedaleus senegalensis , Zonocerus variegatus , Nomadacris septemfasciata and Chortoicetes terminifera. Mortality predictions were accurate to a 2-day error in every 10 days. This level of resolution is satisfactory to guide operational use of the biopesticide. 4 The model was subsequently used for a prospective evaluation of the performance of M. anisopliae var. acridum against two additional pest species, Dociostaurus maroccanus and Calliptamus italicus in Spain. Results suggest that this pathogen would work reasonably well against these species as long as early instars are targeted. 5 The model could provide a useful tool to assist in interpreting effectiveness of control operations, develop improved application strategies to optimize the performance of the biopesticide and identify appropriate target species and environments.
Effects of Temperature and Thermoregulation on Mycosis by Beauveria bassianain Grasshoppers
Biological Control, 1996
The influence of behavioral thermoregulation by grasshoppers (Melanoplus sanguinipes) on mycosis caused by Beauveria bassiana was investigated in controlled environments. The cardinal temperature for B. bassiana conidial germination and hyphal development was approximately 35°C. A low prevalence of mycosis (I7%) was observed in inoculated nymphs exposed to a continuous temperature of 35 and 40°C, whereas continuous exposure to 30°C did not have a significant effect on disease development. Daily exposures to 35 and 40°C for 1 and 6 h, respectively, decreased mycosis in nymphs. In both environments, a strong correlation (r H 0.95) was observed between hyphal growth on potato dextrose agar and final mycosis. Although high temperatures delayed conidial germination, only conidia exposed to continuous 35 or to 40°C for more than 8 h exhibited reduced germination after 24 h. The effects of temperature on conidial germination were poorly correlated with disease, and when nymphs were exposed to 35°C for 24 h, less mycosis was observed only in grasshoppers exposed between 1 and 2 days postinoculation. The thoracic temperature of nymphs permitted to bask adjacent to a heat source ranged from 38 to 42°C. In nymphs basking for 1 h per day, 46% less mycosis was observed, decreasing to 98% less disease in nymphs allowed to bask for 6 h or greater per day. On a heat gradient, a higher prevalence of B. bassiana-infected nymphs selected hotter positions than noninfected nymphs, suggesting a ''behavioral fever'' response to infection. This study indicates that high temperature and thermoregulation can adversely affect B. bassiana mycosis of grasshoppers and may explain the poor efficacy of this entomopathogen observed in some field experiments. r
Behavioral thermoregulation in the migratory locust: a therapy to overcome fungal infection
Oecologia, 2004
We examined under laboratory conditions the thermopreference of the migratory locust, Locusta migratoria migratorioides, following infection by the entomopathogenic fungus Metarhizium anisopliae var. acridum and its influence on mycosis. Infected locusts raised their body temperature more frequently than healthy conspecifics through selection of high temperatures in a heat gradient. Thermoregulation did not, however, alter the frequency of feeding events nor the amount of food eaten by infected L. migratoria. A thermoregulation regime of a minimum of 4 h/day substantially increased survival of inoculated insects (by 85%). However, the therapeutic effect decreased when thermoregulation was delayed following inoculation of the pathogen. Thermoregulation reduced locust mortality but did not completely eliminate the fungus from infected hosts; the fungus grew and killed the insects when thermoregulation was interrupted. We suggest that periodic, short bouts of thermoregulation, when performed from the onset of infection and for an extended period of time, are sufficient to provide a therapeutic effect to infected hosts. Such thermoregulatory capacity of locusts may limit the potential of fungal pathogens as biological control agents under certain ecological conditions.
Environmental Entomology, 1997
The influence of environmental conditions on mycosis of grasshoppers caused by Beauveria bassiana (Balsamo) Vuillemin, was investigated. Despite the deposition of considerable quantities of conidia onto grasshoppers (6.7 X 10 3 colony-forming units [CFU] per nymph), B. bassiana did not significantly reduce field populations nor did it affect specific grasshopper taxa. Conditions were warm and sunny during the trial, and slopes of conidial persistence were equally poor on both grasshoppers and grass leaves. Small numbers of conidia «2 CFU per grasshopper) were recovered from surface-sterilized grasshoppers 5-15 dafter application indicating that if infection occurred, B. bassiana did not proliferate in the hemo-coe\. Considerable mycosis was observed in grasshoppers placed in cages in the greenhouse, but not in grasshoppers confined in cages adjacent to the field plots. Furthermore, the prevalence of disease in the greenhouse cages decreased with the sampling date but the onset of mycosis always occurred 3-4 d after collection, suggesting that environmental conditions in the greenhouse were responsible for the increased susceptibility of grasshoppers. Higher prevalence and more rapid development of disease were observed in grasshoppers placed in shaded cages (83-89%) than in cages exposed to full sunlight (0-15%) or protected from UVB radiation (1-43%); conidial survival was equally enhanced in the shaded and UVB-protected environments. Our results indicate that the poor efficacy of B. bassiana against rangeland grasshoppers was a result of conditions of temperature and light exposure (reduced grasshopper thermoregulation), and not the result of inadequate host targeting or pathogen virulence.
Biological Control, 1997
The influences of temperature on the mortality of grasshoppers (Melanoplus sanguinipes) inoculated with the entomopathogenic fungi, Beauveria bassiana and Metarhizium flavoviride, alone and in combination was investigated. Basking by grasshoppers had less influence on the prevalence and timing of mortality in nymphs treated with M. flavoviride than with B. bassiana. In B. bassiana-treated nymphs allowed to bask for only 1 h/day, 44% less mortality was observed, decreasing to 98% less death in nymphs basking for H4 h/day. In contrast, only a slight decrease in mortality (13 to 23%) was observed in M. flavoviride-treated nymphs permitted to bask for 4 to 6 h/day. For both fungi, more mortality was observed in nymphs exposed to 35 than to 40°C for various durations per day. However, exposure to high temperatures had a greater inhibitory effect on B. bassiana than M. flavoviride. The efficacy of both entomopathogens, alone and in combination, was determined in simulated cool and hot fluctuating temperature environments and at a constant 25°C. The former two environments were derived from weather data on two different days at Lethbridge in July and were adjusted to simulate grasshopper thermoregulation during daylight periods (0600 to 2200 h). At 25°C, there was no difference between treatments in the prevalence of mortality. In the hot temperature environment, less mortality was observed for B. bassiana (3%) than for M. flavoviride (52%). Conversely, in the cool temperature environment, less mortality was observed for M. flavoviride (46%) than for B. bassiana (100%). Application of both pathogens simultaneously resulted in a final prevalence of mortality that was greater than that for M. flavoviride in the hot temperature environment and equal to that for B. bassiana in the cool temperature environment. The application of B. bassiana and M. flavoviride in combination may be a way to overcome some of the constraints of temperature on entomopathogenic Hyphomycetes against grasshoppers, especially where temperatures fluctuate or are high for a significant period of time. r 1997 Academic Press
Thermal biology in insect-parasite interactions
Trends in Ecology & Evolution, 2003
Recently, several applied studies exploring the use of pathogens for insect biocontrol have demonstrated significant effects of environmental temperature on the outcome of infection. For example, host resistance, host recovery, pathogen virulence and replication can alter considerably with sometimes very small changes in temperature. Moreover, the effectiveness of certain insect parasitoids and the activity of endosymbionts can vary across the range of realistic temperatures experienced in the field. These responses are not necessarily linear or immediately predictable, because they derive from a complex 'genotype-by-genotype-byenvironment' interaction. Given the importance of parameters such as virulence and resistance in determining the course of a host-parasite interaction, such effects of temperature could have profound implications for host -parasite dynamics and coevolution.
The role of fungi in the control of grasshoppers
Botany-botanique, 1995
Fungi are among the most important microbial pathogens of grasshoppers with potential for development as biological control agents. Unlike most other insect pathogens that must be ingested to initiate disease, fungi generally invade insects via the external cuticle. The most common fungi that are pathogenic to grasshoppers are Beauveria bassiana, Metarhiziwn anisopliae, Metarhizium flavoviride, Sorosporella sp., and fungi in the E~itomophaga grylli complex. A review of the latest information on the development of these fungi as microbial control agents of grasshoppers is presented. Species in the E. grylli complex are being used in classical biocontrol. This has resulted in controversy as there are indigenous nonpest grasshopper species that may be affected through introduction of the nonindigenous fungal strains. Beauveria bassiana and M. flavoviride are being developed for inundative control. These fungi can be mass produced and applied with equipment used for conventional pesticides. Conidia are applied either at ultralow volume in oil, as oil emulsions, or as bran-bait formulations. Field trials in Africa and North America have demonstrated significant grasshopper reductions. Improvements in formulation and inoculum targeting may further improve their efficacy.