Dan L. Johnson

Global decomposition experiment shows soil animal impacts on decomposition are climate-dependent

Climate and litter quality are primary drivers of terrestrial decomposition and, based on evidence from multisite experiments at regional and global scales, are universally factored into global decomposition models. In contrast, soil animals are considered key regulators of decomposition at local scales but their role at larger scales is unresolved. Soil animals are consequently excluded from global models of organic mineralization processes. Incomplete assessment of the roles of soil animals stems from the difficulties of manipulating invertebrate animals experimentally across large geographic gradients. This is compounded by deficient or inconsistent taxonomy. We report a global decomposition experiment to assess the importance of soil animals in C mineralization, in which a common grass litter substrate was exposed to natural decomposition in either control or reduced animal treatments across 30 sites distributed from 43°S to 68°N on six continents. Animals in the mesofaunal size range were recovered from the litter by Tullgren extraction and identified to common specifications, mostly at the ordinal level. The design of the trials enabled faunal contribution to be evaluated against abiotic parameters between sites. Soil animals increase decomposition rates in temperate and wet tropical climates, but have neutral effects where temperature or moisture constrain biological activity. Our findings highlight that faunal influences on decomposition are dependent on prevailing climatic conditions. We conclude that (1) inclusion of soil animals will improve the predictive capabilities of region- or biome-scale decomposition models, (2) soil animal influences on decomposition are important at the regional scale when attempting to predict global change scenarios, and (3) the statistical relationship between decomposition rates and climate, at the global scale, is robust against changes in soil faunal abundance and diversity.

Reduction of grasshopper populations following field application of the fungus Beauveria bassiana

Conidia of the Hyphomycete fungus Beauveria bassiana (Bals.) were applied in an attempt to reduce field populations of grasshoppers, primarily the migratory grasshopper Melanoplus sanguinipes (Fabricius). Dry spores were applied with wheat bran carrier to three fallow fields at a rate of 2.0 × 1013 spores ha−1 in 10 kg bait ha−1. Examination of culture plates that had been placed in the field to capture spores and of bran carrier with scanning electron microscopy indicated that a substantial portion of the B. bassiana colony—forming units (spores and clumps of spores) did not adhere to the bran and were applied in the field as free particles. Grasshoppers collected from the treated plots at intervals after application were assayed for infection by B. bassiana. The observed rate of mycosis in the treated populations was 70% of those collected after 2 days, declining to 41% by 13 days and 5% by 19 days after application. Analysis of reductions in population density gave results in agreement with the infecti...

Effect of Bait Substrate and Formulation on Infection of Grasshopper Nymphs by Beauveria bassiana

The effects of two formulations (oil and water) and two bait substrates (lettuce and bran) on infection of grasshopper nymphs (Melanoplus sanguinipes) by Beauveria bassiana were investigated. More nymphs died of mycosis after they had ingested substrates inoculated with conidia in oil than in water, but there was no difference between the lettuce and bran substrates. Of the conidia recovered in frass, most (95%) were recovered within 24 h of ingestion of the lettuce and bran substrates by nymphs. Significantly more conidia averaged over time were recovered in frass from the water than from the oil formulation. A higher incidence (33-82%) and more rapid onset of mycosis was observed in nymphs that were surface-sterilized before ingestion, compared with those surface-sterilized after ingestion of lettuce and bran substrates inoculated with B. bassiana in both formulations. A similar trend was observed in nymphs receiving the sterilization treatment before, rather than after, ingestion of wheat leaves spraye...

Behavioural optimization of body temperature by nymphal grasshoppers (Melanoplus sanguinipes, Orthoptera: Acrididae) in temperature gradients established using incandescent bulbs

1. 1. Body temperatures (Tb) of Melanoplus sanguinipes F. nymphs were measured in temperature gradients established using incandescent light bulbs. 2. 2. Relative frequency distributions of possible Tb were estimated by linking equations describing the effects of distance from the light bulb and orientation to it. 3. 3. The distribution of Tb was significantly different from that expected if insects positioned themselves randomly, and 35 ≤ Tb ≤ 43°C occurred more frequently than expected; this is conclusive evidence for behavioural thermoregulation. 4. 4. The modal Tb, 40°C, approximated the temperatures for maximum rates of feeding (38.6°C) and development (42.2°C); at 40°C, both rates occur at > 95% of their maximum rate.

Effects of Simulated Rain on the Persistence of Beauveria bassiana Conidia on Leaves of Alfalfa and Wheat

The effect of simulated rain at two intensities (26.7 or 112.7 mm h-1) and durations (30 or 60 min) on the persistence of Beauveria bassiana conidia applied in water on leaves of alfalfa leaves of alfalfa (Medicago sativa) or wheat (Triticum aestivum) was investigated. Initial populations of conidia on the leaves of both crops were similar, and ranged from 1.7 105 to 3.5 105 colony-forming units cm-2. The simulated rain reduced the concentration of conidia on leaves by 28-61%. Although there was a slight effect due to rain intensity for alfalfa, there was no influence of either rain duration or crop type on the retention of B. bassiana conidia.

Development of a PCR-based diagnostic assay for the specific detection of the entomopathogenic fungus Metarhizium anisopliae var. acridum

The entomopathogenic fungus Metarhizium anisopliae var. acridum is registered as a mycopesticide for acridid control in Africa and Australia. Traditionally, identification of M. anisopliae var. acridum infection in grasshoppers and locusts has relied upon development of fungal growth in infected cadavers. Conventional methods of detection of this entomopathogen in the environment and non-target organisms have been based on culture and bioassay. A PCR-based method for the detection of M. anisopliae var. acridum was developed. Sequence data from the distinct ITS rDNA regions facilitated the design of PCR primers that were used in PCR-based diagnostic assays for the detection of fungal DNA. The amplified sequence was 420 bp in length and specific to M. anisopliae var. acridum. Isolates of M. anisopliae var. anisopliae and M. flavoviride produced no PCR product with these primers. Other fungal entomopathogens, plant pathogens, mycopathogens, and soil saprophytes were also not detected by the pathogen-specific primers. The assay was also effective for the detection of M. anisopliae var. acridum DNA in the presence of soil DNA extracts and in infected grasshoppers.

The Effects of Timing and Frequency of Application of Nosema locustae (Microspora: Microsporida) on the Infection Rate and Activity of Grasshoppers (Orthoptera: Acrididae)

The influence of the timing of application of spores of Nosema locustae on the prevalence and degree of infection of grasshoppers was assessed in a field experiment. The application treatments were early season, late-season, double (both early and late), and no bait (untreated). To assess effects on population density and activity, two methods of sampling were used: density estimates based on permanent quadrats, and sequential sampling in which the number of sweeps required to collect 100 grasshoppers was recorded. Late-season application resulted in a higher prevalence of infection than did early application. The degree of infection was also a function of timing: lateseason application resulted in more moderate to heavy infections than did early application. The infection rates that resulted from double application did not diier significantly from that of lateseason application. Application of N. locustae provided moderate reductions, ca. 30%, in grasshopper density. Differences in the required sweep sampling effort were greater, suggesting that reduction in grasshopper activity was caused by the disease.

PATHOLOGICAL AND PHYSIOLOGICAL RESPONSES OF RING-NECKED PHEASANT CHICKS FOLLOWING DIETARY EXPOSURE TO THE FUNGUS METARHIZIUM FLAVOVIRIDE, A BIOCONTROL AGENT FOR LOCUSTS IN AFRICA

Metarhizium flavoviride, a fungal pathogen of grasshoppers and locusts, appears to be an effective, non-chemical insecticide (mycoinsecticide) for control of grasshoppers and locusts. This study, conducted during June and July, 1997, examined the pathogenic potential of this entomopathogenic fungus to non-target avian species that encounter infected insect prey items or contaminated food sources. Ring-necked pheasant (Phasianus colchicus) chicks were exposed to one of three diets, (spore-coated feed, infected insects, or untreated feed), either from 4 to 9 days of age, or, from 35 to 40 days of age. Necropsies were conducted on birds 10 days and 46 days old, respectively. Neither consumption of infected insects, nor of spore-coated feed, resulted in pathological changes, or significant changes in weight, growth rate, behavior, or mortality rate. Histological examination of organs indicated either no changes related to treatment, or normal tissue responses to antigenic challenge.

Indirect effects of the pyrethroid insecticide deltamethrin on reproductive success of chestnut-collared longspurs

An experiment was conducted to determine whether spraying with a broad-spectrum pyrethroid insecticide in grassland habitat for the control of grasshoppers could affect nesting songbirds through the removel of insect food resources. Three 81 ha plots were sprayed at the recommended rate of Decis 5F (6.25 g deltamethrin ha−1). Paired control plots remained unsprayed. The density of (Acrididae) grasshoppers was monitored throughout the spring and summer. The nests of chestnut-collared longspurs (Calcarius ornatus) were monitored to determine the nest and nestling survival rates, size at fledging and food habits. Attributes of parental foraging were quantified. Food selection by parents and consumption by nestlings were measured using oesophageal ligatures. Grasshoppers accounted for >85% of the biomass of the nestling diet to spraying and this proportion increased throughout the season in unsprayed plots. Applications of Decis 5F initially reduced the grasshopper density by 93%. After spraying, parent birds switched to other arthropod taxa less affected by insecticide application; the overall biomass fed to nestlings was not significantly reduced although the acridid proportion declined to <30%. The weight and skeletal size of the nestlings at fledging was unaffected. Parent birds in sprayed plots flew no further to feed their nestlings at a similar rate to that of birds in the control plots. The clutch size and nestling survival were similar between the sprayed and unsprayed plots after Decis 5F application, but egg success was lower in the sprayed plots compared to the control plots (67 versus 87%, p < 0.05)

CONVECTIVE HEAT LOSS AND CHANGE IN BODY TEMPERATURE OF GRASSHOPPER AND LOCUST NYMPHS: RELATIVE IMPORTANCE OF WIND SPEED, INSECT SIZE AND INSECT ORIENTATION

1. 1. Grasshopper (Melanoplus sanguinipes, M. bivittatus) and locust (Locusta migratoria migratorioides) (Orthoptera: Acrididae) nymphs were oriented at angles to the wind stream at four wind speeds. 2. 2. Rates of temperature and energy change due to convection were measured after compensating for Stefan-Boltzmann radiative energy exchange. 3. 3. The rate constant for Newtons law of cooling, and the convective heat-transfer coefficient were both affected nonlinearly by insect size and wind speed, but were not significantly affected by insect orientation to the wind. 4. 4. Comparison with published information suggests that the relationships observed apply widely within the animal kingdom.