High Insect Densities Research Articles

Coastal landforms and fetch influence shoreline restoration effectiveness

Coastal shorelines are a key interface between terrestrial and aquatic ecosystems and are vital for human livelihood. As a result, shorelines have experienced substantial human modifications worldwide. Shoreline “hardening” – the construction of armor including seawalls, bulkheads, or rip-rap – is a common modification that has substantial negative ecological effects. Currently, restoration involving the removal of armor and replacement with “living” shorelines is becoming an established practice. Still, the ecological response to armor removal is oftentimes unpredictable and site-specific. We hypothesized that the confluence of larger-scale geophysical features might strongly influence ecological restoration outcomes at particular locations. To measure the effectiveness of armor removal in the context of broad-scale geophysical features across the Salish Sea, WA, USA, we studied 26 paired restored and natural reference beaches of the same shoretype (feeder bluff, accretion shoreform, or pocket beach), as well as corresponding fetch, sub-basin, and percent of shoreline sediment drift cell armored. Sites were restored for an average of six years. We gauged restoration effectiveness based on levels of five ecological response variables: beach wrack (percent, depth), logs (count, width), sediments (percent sand), vegetation (percent overhanging, count of fallen trees), and insects (density, taxa richness). We found that armor removal often restored these variables to natural levels, but that restoration response was dependent on geophysical features such as shoretype and fetch. Natural beaches did have higher measurements of overhanging vegetation, fallen trees, and insect taxa richness, as these features likely take time to mature at restored beaches. Feeder bluffs had a higher proportion of surface sand and number of fallen trees than other shoretypes, coinciding with the erosion of bluff material, whereas natural pocket beaches within bordering rocky headlands had higher insect densities. Sites with a large fetch had higher input of deposited wrack and logs, whereas sites with a small fetch had higher input from localized terrestrial sources – fallen trees and eroding sand. By incorporating the effectiveness of restoration with landscape features such as shoretype and fetch, we can more effectively plan for future restoration actions and better predict their outcomes.

Reproduction deep inside wood: a low O2 and high CO2 environment promotes egg production by termite queens.

Extreme conditions are normal for animals living in harsh environments. These animals adapt to their habitats and can use difficult conditions by default. Organisms living in enclosed spaces, notably termites in decaying wood, experience low O2 and high CO2 gas conditions due to limited gas exchange and high insect density. Termite queens, in particular, reproduce in royal chambers deep inside the wood, wherein tens of thousands of individuals engage in social labour. Here, we demonstrate that royal chambers in termite nests have low O2 and high CO2 gas concentrations, which enhance egg production by queens. We identified a unique gas condition of royal chambers in the nest of the subterranean termite Reticulitermes speratus, which is characterized by low O2 (15.75%) and high CO2 (4.99%) concentrations. Queens showed significantly greater fecundity under the low O2 and high CO2 gas conditions in the royal chambers than under ambient gas conditions. Quantitative PCR analysis revealed that the royal chamber gas conditions significantly promoted the expression levels of the vitellogenin genes RsVg1, RsVg2 and RsVg3 in queens compared with ambient gas conditions. This study highlights the adaptation of animals that live in closed habitats, which are hypoxic and hypercapnic as the result of their own metabolism, so as to have a high fitness in such environmental conditions.

Differential wing polyphenism adaptation across life stages under extreme high temperatures in corn leaf aphid

Polyphenism, a common phenomenon in nature, is an important form of adaptation in a diverse environment. Corn leaf aphid (CLA), Rhopalosiphum maidis, (Hemiptera: Aphididae), exhibit wing polyphenism in response to poor habitat quality. In this study, we focused on the effects of crowding and thermal cues on morph determination of CLA. Five developmental stages of aphids (1st to 4th nymphs and maternal adults) with increased population densities, were tested under two kinds of temperature patterns, i.e., A) a constant temperature of 22 °C with 2 h exposure to high temperature in the range of 35 to 39 °C during mid-photophase and B) different constant temperatures in the range of 22–30 °C with 2 h exposure to high temperature of 39 °C during mid-photophase. Crowding was found to directly impact winged induction. The 1st and 2nd nymphs were more sensitive for alate morphs induction under high density. In addition, temperature played a significant role in wing production, with the temperature setting of 26/39 °C in pattern B inducing higher alate morphs and survival than other temperature settings. Therefore, we hypothesize that warmer climate with brief high temperature is more favourable for survival and alate morphs production, but cool weather and transient extreme high temperature (>39 °C) is detrimental for CLA. Our results provide a new perspective on understanding the interactions between changes in extreme high temperatures and insect densities that differentially affect wing polymorphism for further demographic and distribution rates of species across temporal and spatial scales.

Migratory bats respond to artificial green light with positive phototaxis.

Artificial light at night is spreading worldwide at unprecedented rates, exposing strictly nocturnal animals such as bats to a novel anthropogenic stressor. Previous studies about the effect of artificial light on bats focused almost exclusively on non-migratory species, yet migratory animals such as birds are known to be largely affected by light pollution. Thus, we conducted a field experiment to evaluate if bat migration is affected by artificial light at night. In late summer, we presented artificial green light of 520 nm wavelength to bats that were migrating south along the shoreline of the Baltic Sea. Using a light on-off treatment, we observed that the activity of Pipistrellus nathusii and P. pygmaeus, the two most abundant migratory species at our site, increased by more than 50% in the light-on compared to the light-off treatment. We observed an increased number of feeding buzzes during the light-on compared to the light-off treatment for P. nathusii. However, feeding activity was low in general and did not increase disproportionately during the light-on treatment in relation to the overall echolocation call activity of bats. Further, P. nathusii were attracted towards the green light at a distance of about 23 m, which is way beyond the echolocation detection range for insects of Nathusius’ bats. We therefore infer that migratory bats were not attracted to artificial green light because of high insect densities, but instead by positive phototaxis. We conclude that artificial light at night may potentially impact bat migration in a yet unrecognized way.

Extreme variations in spring temperature affect ecosystem regulating services provided by birds during migration

Extreme weather is becoming more pronounced, making phenological patterns less predictable. Among the potential consequences, extreme weather may alter relationships of migratory birds with their seasonal food resources and thus impact valuable ecosystem regulating services (e.g., bird predation of herbivorous insects). Our goal was to quantify the effect of an extremely warm spring on these relationships in a U.S Midwest oak savanna. Average regional temperatures in the spring of 2009 coupled with record highs in 2010 (8°C warmer) were the basis of a natural experiment for addressing our goal. In both springs we documented tree flowering and leaf‐out phenology, related these to arrival and foraging behavior of the three most abundant migratory wood‐warbler species (Parulidae), and quantified the effects of migratory bird foraging on insect density, size, and herbivory using a branch exclosure experiment. In 2009, the dominant tree species at our study site, eastern black oak (Quercus velutina), flowered in mid‐May and the wood warblers foraged heavily in the savanna during this time. Branches from which birds were excluded exhibited a trend toward higher insect density, larger Lepidopterans, and greater flower damage than control branches. In 2010, tree phenology was four weeks earlier than in 2009 and the wood warblers were nearly absent from the savanna (83% fewer), likely because peak food availability preceded their arrival in mid‐May. Insect density was 83% greater in 2009 than 2010. However, in 2010, 81% of sampled leaves exhibited substantial damage (>25% of leaf‐area removed) compared with 27% of leaves in 2009, presumably due to a lack of herbivorous insect regulation by birds. Our results suggest that the extremely warm spring of 2010 altered linkages between migratory birds and their invertebrate prey that are typical during years of average weather, which likely affected habitat use and the delivery of ecosystem regulating services.

An Insect-Feeding Guild of Carnivorous Plants and Spiders: Does Optimal Foraging Lead to Competition or Facilitation?

Carnivorous plants and spiders, along with their prey, are main players in an insect-feeding guild found on acidic, poorly drained soils in disturbed habitat. Darwin's notion that these plants must actively attract the insects they capture raises the possibility that spiders could benefit from proximity to prey hotspots created by the plants. Alternatively, carnivorous plants and spiders may deplete prey locally or (through insect redistribution) more widely, reducing each other's gain rates from predation. Here, we formulate and analyze a model of this guild, parameterized for carnivorous sundews and lycosid spiders, under assumptions of random movement by insects and optimal foraging by predators. Optimal foraging here involves gain maximization via trap investment (optimal web sizes and sundew trichome densities) and an ideal free distribution of spiders between areas with and without sundews. We find no facilitation: spiders and sundews engage in intense exploitation competition. Insect attraction by plants modestly increases sundew gain rates but slightly decreases spider gain rates. In the absence of population size structure, optimal spider redistribution between areas with and without sundews yields web sizes that are identical for all spiders, regardless of proximity to sundews. Web-building spiders have higher gain rates than wandering spiders in this system at high insect densities, but wandering spiders have the advantage at low insect densities. Results are complex, indicating that predictions to be tested empirically must be based on careful quantitative assessment.

Characterization of volatile organic compounds released by granivorous insects in stored wheat

Identification of the volatile organic compounds released by insects can be used to detect insects in stored grains. An attempt was made to identify the volatile organic compounds released by Tribolium castaneum (red flour beetle) and Cryptolestes ferrugineus (rusty grain beetle) by headspace analysis. Feasibility of the automatic headspace sampler in headspace analysis was found to be positive. The amount of volatiles produced by T. castaneum adults increased with an increase in insect density. The concentration of methyl-1,4-benzoquinone; ethyl-1,4-benzoquinone; and 1-tridecene released by ten adult insects were: 8.5, 9.1 and 10.6 μg/100 μL compared to 7, 8 and 4.2 μg/100 μL for five adult insects. Extreme high or low temperature leading to death produced very high amounts of volatiles compared to insects kept at 35 °C. The larvae of the T. castaneum insects did not produce any volatiles at ambient condition or at extreme cold or hot condition. The C. ferrugineus adults did not produce any detectable amount of volatiles even at very high insect density after up to 3 days. The results of the combination of T. castaneum and C. ferrugineus insects gave the same volatile compounds as produced by T. castaneum insects alone.

Three-dimensional spatial distribution of adults of Cryptolestes ferrugineus (Coleoptera: Laemophloeidae) in stored wheat under different temperatures, moisture contents, and adult densities

Spatial and temporal distributions of adults of Cryptolestes ferrugineus in stored wheat were determined in a 1.5 t bin of wheat held at 20, 25 and 30 °C and 11%, 13% and 15% grain moisture contents (wet basis). The introduced insect densities were 0.1 (low), 1.0 (medium), and 10.0 (high) adults/kg wheat and the 1.5 t of wheat was sampled at 5 locations with 45 kg in a sample unit (referred to as primary unit, about 15% of the wheat was sampled). At each location, the 45 kg sample unit was separated into three 15 kg vertical layers (referred to as subunits). Geostatistical analysis showed that: 1) insect numbers at medium or high density and in the vertical direction were better correlated than that at low insect density and in the horizontal direction, respectively; 2) this correlation decreased with increasing grain temperatures; and 3) the temporal continuous property might not exist or there was a weak temporal continuity. Aggregation was the highest at the low insect density and then decreased with the increase of insect density due to a repelling effect amongst adults at high insect density. The normal distribution model was appropriate for the description of the count frequency in 32 out of 36 sampling sets (88.9%) when 15 kg subunit data were used. In addition, adults of C. ferrugineus had clumped distribution about 95% of the time and uniform dispersion about 5% of the time. This is the first research illustrating the spatial and temporal distributions of adult C. ferrugineus using large sample units and known insect densities.

Facilitation vs. apparent competition: insect herbivory alters tree seedling recruitment under nurse shrubs in a steppe–woodland ecotone

Summary 1. Facilitation of recruitment by ‘nurse’ plants can play a major role in harsh environments. Yet the extent to which consumer‐mediated apparent competition from habitat‐forming plants may counteract facilitative interactions remains largely unexplored. 2. We examined whether seedling predation by tenebrionid beetles seeking refuge under nurse shrubs may prevent tree recruitment facilitation in a Patagonian steppe–woodland ecotone. Newly emerged seedlings of Austrocedrus chilensis were planted in shrub canopy, off‐shrub shelter and bare soil microsites, and monitored for causes of early mortality and for overall survival under ambient and elevated beetle densities. 3. Most seedlings in open microsites died from abiotic stress, whereas shrub cover and artificial shelters decreased desiccation mortality. Herbivory was the main cause of mortality in shrub microsites. Beetle addition increased predation beneath shrubs and in off‐shrub shelters, indicating that apparent competition ‘spilled over’ from shrubs with high insect densities. 4. Litter removal from shrubs prevented seedling predation suggesting that nurse plants altered recruitment by providing food as well as shelter to insects. Herbivory rates did not depend on seedling patch density but decreased with seedling age, with 1‐week old plants being most vulnerable to beetle predation. 5. Synthesis. Apparent competition from nurse plants can strongly reduce recruitment facilitation in stressful environments, although weak herbivore density dependence and seedling growth into ontogenetic refuges may limit the strength of apparent competition. An explicit consideration of negative, as well as positive, herbivore‐mediated indirect effects from habitat‐forming plants would broaden the understanding of community dynamics along stress gradients.

Stored Grain Advisor Pro: Decision support system for insect management in commercial grain elevators

A decision support system, Stored Grain Advisor Pro (SGA Pro) was developed to provide insect pest management information for wheat stored at commercial elevators. The program uses a model to predict future risk based on current insect density, grain temperature and moisture. A rule-based system was used to provide advice and recommendations to grain managers. The software was tested in a research program conducted at commercial grain elevators in Kansas and Oklahoma, USA. A vacuum-probe sampler was used to take ten 3-kg grain samples in the top 12 m of each bin that contained wheat. After the insect species and numbers were determined for each sample, the data were entered into SGA Pro. A risk analysis and treatment recommendation report for all bins was presented to the grain managers every 6 weeks. SGA Pro correctly predicted for 71–80% of bins whether the grain was safe or at high risk of dense infestation and grain damage. SGA Pro failed to predict “unsafe” insect densities in only 2 out of 399 Kansas bins (0.5%) and in none of 114 bins in Oklahoma. Grain managers who followed SGA Pro's recommendations tended to fumigate only the bins with high insect densities instead of fumigating all bins at their facility. This resulted in more efficient insect pest management because fumigating bins only when insect densities exceeded economic thresholds and treating only the bins that required fumigation minimized the risk of economic losses from insects, reduced the cost of pest management, and reduced the use of grain fumigant.

Development of a treatment threshold for sucking insects in determinate Bollgard II transgenic cotton grown in winter production areas

Abstract Little is known about the impact of sucking insects on cotton grown in tropical production areas. To examine this, an experiment was conducted at Katherine in northern Australia to determine the impact of mirids (Creontiades dilutus (Stål) and Creontiades pacificus (Stål), green vegetable bug (Nezara veridula (L.)) and red‐banded shield bug (Piezodorus hybneri (Gmelin)) on the yield and fibre quality of the transgenic cotton variety DP50bx containing genes for the expression of Cry1A(c) and Cry2A(b) δ‐endotoxins of Bacillus thuringiensis Berliner variety kurstaki. The trial examined the impact of sucking insect populations in the range 0.5–2.0/m2. Yields of unsprayed plots were approximately 30% of those obtained in plots sprayed on a threshold of 0.5/m2 which did not differ significantly from plots sprayed regularly to exclude sucking insects. The increase in yield in the low pest density treatments was the result of improved fruit retention in the middle part of the plant. Fibre quality was similar in all treatments. However, damage ratings to individual bolls did differ between treatments. Bolls in the high insect density treatments received more damage than those in the low density treatments. As a result of this study, a tentative treatment threshold of 0.5 sucking insect/m2 is recommended in determinate Bollgard II cotton varieties grown in winter production areas.

Bell-miner-associated dieback at the tree crown scale: a multi-trophic process

Summary This paper examines some of the factors and processes which interact within eucalypt stands affected by bell-miner-associated dieback. A key symptom of this form of dieback is sustained foliar damage from herbivorous insects, in particular psyllids. Repeated cycles of defoliation/refoliation result in branch death and crown contraction. Weakened trees become more susceptible to secondary stressors such as wood borers, soil fungal pathogens and abnormal levels of soil moisture. Psyllid outbreaks can occur through a reduction in the efficacy of their natural enemy complex, and the provision of sufficient favourable foliage to sustain high insect populations. The young foliage preferred for feeding and oviposition by most eucalypt insect herbivores can occur when soil moisture and nutrients and canopy irradiation are non-limiting. Bell miner colonies require high insect densities in their food source and they reinforce this situation through their feeding behaviour and territorial defence. The study suggests the effect of bell miners on the populations of herbivorous insects, and hence the amount of insect-damaged foliage, is density dependent. Bell miners also require dense understorey, about 2–5 m high, for nesting sites, and the presence of surface water. Any management practice that reduces bell miner density will in turn reduce the density of insect herbivores and hence foliar damage in the eucalypt tree crowns. Then, if the trees have not become too debilitated, crown recovery is likely to occur.

Movement and distribution of adult rusty grain beetle, Cryptolestes ferrugineus (Coleoptera: Laemophloeidae), in stored wheat in response to different temperature gradients and insect densities.

The movement and distribution of adult Cryptolestes ferrugineus (Stephens) (Coleoptera: Laemophloeidae) in grain provide important information for detection of insect pests and for simulations of their distribution in grain bins. Adult movement and distribution were determined in 100 by 100 by 1000-mm wheat (14.5 +/- 0.2% moisture content) columns at four insect densities, three temperature gradients, and dynamic (changing) temperature conditions. Insect density was a minor factor influencing insect movement and distribution in grain columns with temperature gradients. Dispersal resulted in a uniform distribution at a higher insect density (higher than two adults per kilogram of wheat), and aggregation occurred at a low insect density. Adults wandered in the first 6 h after introduction, and there were fewer adults wandering in the vertical direction than in the horizontal direction. Adults moved faster in the vertical direction than in the horizontal direction, and the maximum speed of the movement was 6 m/d in the horizontal direction, and >10.8 m/d in the vertical direction through wheat. Adults could detect temperature gradients in <1 h and preferred warmer temperatures when they had a choice. Insect distribution in horizontal wheat columns at any temperature gradient was unstable for 24 h. Twenty-four hours after introduction, adults gradually overcame their positive geotactic behavior if the upper temperature was more biologically suitable or was not <27.5 degrees C. Adults responded faster to higher temperature gradients than to lower temperature gradients. There was a similar pattern of adult distribution in 144 h.

Intra- and interspecific interactions among Tribolium castaneum and Cryptolestes ferrugineus in stored wheat at different insect densities

Cryptolestes ferrugineus and Tribolium castaneum are important economical pests of stored grain in Canada. Insects were reared separately or together on hard red spring wheat at three insect densities representing 1000, 500, and 250 adults per kilogram of wheat for single species and twice that of single densities for mixed species, in the laboratory (30°C, 70% RH). The experiment was conducted on dry (12% moisture content [MC], wet basis) and damp wheat (15% MC, wet basis). Adults were sampled every 2 weeks over a 10-week period. Sifted wheat was incubated at 30°C, 70% RH for 4 weeks to observe the number of adults emerging from immatures present under the seed coat of the wheat germ. All experiments were replicated four times. Initial insect densities, moisture content, and species combination had significant effects on the resulting adult population. Adult numbers for both species were higher on 15% MC wheat. In 12% MC wheat, T. castaneum numbers were higher than C. ferrugineus numbers when reared separately whereas this was reversed in 15% MC grain. Cryptolestes ferrugineus populations were significantly higher when reared with T. castaneum than when reared as a single species on 12% MC grain. The trend was reversed in 15% MC grain. At both grain moistures, T. castaneum numbers were higher as an isolated species compared to when reared with C. ferrugineus. The study suggested that T. castaneum populations were inhibited in the presence of C. ferrugineus. High insect density often accentuated these effects.

TransgenicBt-producingBrassica napus:Plutella xylostellaselection pressure and fitness of weedy relatives

Release of transgenic insect-resistant crops creates the potential not only for the insect pest to evolve resistance but for the escape of transgenes that may confer novel or enhanced fitness-related traits through hybridization with their wild relatives. The differential response of diamondback moth (Plutella xylostella) populations in eastern and western Canada to Bt-producing (GT) Brassica napus and the potential for enhanced fitness of GT B. napus and weedy GT Brassica rapa x B. napus hybrid populations (F1, BC1, BC2) were studied. Comparative bioassays using neonates and 4th instars showed that GT B. napus and GT B. rapa x B. napus hybrids are lethal to larvae from both populations. No measurable plant fitness advantage (reproductive dry weight) was observed for GT B. napus (crop) and GT B. rapa x B. napus hybrid populations at low insect pressure (1 larva per leaf). At high insect densities (>10 larvae per leaf), vegetative plant weight was not significantly different for GT B. napus and non-GT B. napus, whereas reproductive plant weight and proportion of reproductive material were significantly higher in GT B. napus. Establishment of the Bt trait in wild B. rapa populations may also increase its competitive advantage under high insect pressure.

Vegetation architecture and redistribution of insects moving on the plant surface

A model for predicting the influence of vegetation architecture on the rate of population spread by insects moving on the plant surface was developed. Vegetation architecture was described using two parameters: (1) the proportion of the total length of connecting plant parts in relation to the total length of all plant parts, and (2) the proportion of the horizontal projection of connecting plant parts in relation to the total length of connecting plant parts. The influence of each parameter on the rate of population spread through the vegetation was quantified separately. The two parameters were then combined to create a model for predicting the impact of vegetation architecture on the rate of population spread. The model was tested by solving the diffusion equation numerically on example structures that differed in architecture. The rate of population spread predicted by the model corresponded well with the numerical solutions. Finally, redistribution of Lygus rugulipennis (Heteroptera: Miridae) nymphs was observed on small arenas of artificial vegetation. Each arena was composed of two types of artificial vegetation, which differed in architecture. The architecture of the vegetation types clearly influenced the distribution of nymphs on the arenas. The model was successful in predicting which vegetation type would have the higher insect density, but it did not always predict the distribution of nymphs exactly.

Insect community organisation in estuaries: the role of the physical environment

Insects are reportedly uncommon in marine habitats and, from a spatial/temporal intercomparison perspective, estuaries are among the least studied. We examined the natural variability seen among insect community organisation in estuaries on both sides of the North Atlantic, and evaluated the role of their physical environments. Community composition was found to be strongly influenced by three physical factors: estuary size, the degree of inundation by incoming tides, and substrate size/stability. Insects formed a significant proportion (17–54%, by numbers) of the benthic community of coarse‐grained‐substratum estuaries, and species richness increased with estuary size. Nymphs/larvae of mayflies, stoneflies, caddisflies, elmid beetles and chironomids dominated channel sites inundated by up to 25% of all incoming tides, but a gradual loss in species richness occurred downstream. However, even the most seaward sites supported high insect densities (up to 25 016 and 5433 m−2, supporting 26 and 4 species, at sites inundated by 75 and 100% of all incoming tides, respectively). Sites covered by tides for between 3 and 5 h twice daily were dominated by orthocladine chironomids, especially of the genus Orthocladius. Chironomid larvae contribute significantly to the diets of some coastal fish species, particularly juvenile flounder and sticklebacks. We present a schematic model summarising the relationships between estuary size, degree of inundation by salt water and insect community structure.

Effects of Water Cations on Treehole Insect Communities

We monitored water sodium concentration ([Na]), water volume, and larval densities of insects in natural treeholes and larval insects in simulated treeholes. In natural treeholes, water [Na] was inversely correlated with mosquito and helodid beetle densities; water [Na] was positively correlated with water volume in 1996. The culicid Aedes triseriatus (Say), the ceratopogonid Culicoides guttipennis (Coquillett), and the syrphid Mallota posticata (F.) were the 1st to colonize simulated treeholes. Denstities of the helodid beetle, Helodes pulchella (Guerin), and Prionocyphon discoideus (Say), were significantly higher and mosquito populations had a significantly higher proportion of early instars in microcosms that were lower in [Na] and [Mg]. On the other hand, more early instars of midges were found in microcosms higher in [Na] and [Mg]. The consistency of the relationship between low [Na] and high insect density in natural treeholes, and the effects of [Na] on microcosm communities, suggest that [Na] and perhaps other cations may be important resources and cues to treehole organisms and may partially determine treehole community structure.

Impact of Ischnodemus falicus (Hemiptera: Lygaeidae) on Photosynthesis and Production of Spartina pectinata Wetlands

Wetlands dominated by the C4 grass. Spartina pectinata (Link), were investigated to quantity the effects of high densities of lsehnodemus falicus (Say) on leaf-level photosynthesis and aboveground biomass production. Photosynthetic rates of plants within heavily infested stands were greatly reduced from that of plants supporting low densities of I. falicus . In early May 1993, photosynthetic rates of S. pectinata with minor I. falicus presence were >30 μmol m−2 s−1 with peak rates of 45 μmo1 m−2 s−1 in mid-June. In nearby infested S. pectinata wetlands, individual plants had rates as low as 5 μmol m−2 s−1 in early May and peak rates of 24 μmol m−2 s−1 in mid-July. Along with reduced photosynthetic rates, plants hosting high insect densities had lower aboveground production than did plants that had low insect densities. In 1994, when insect densities were ubiquitously low, there were no differences in peak photosynthetic rates or biomass accumulation between stands of S. pectinata that had been host to high versus low densities of insects in 1993. Thus, although infestation of I. falicus on S. pectinata had significant short–term effects, the lack of a long–term effect suggests that S. pectinata can successfully deal with periodic insect outbreaks.

Relationships between insecticide use, grain hygiene and insecticide resistance in Oryzaephilus surinamensis (L.) (Coleoptera: Silvanidae) on grain-producing farms

Levels of resistance in Oryzaephilus surinamensis were related to grain treatments and hygiene practices on 63 grain-producing farms in New South Wales, Australia. Grain-protectant treatment was generally effective in reducing infestation levels. Hygiene measures by themselves had little effect on infestation levels, but good hygiene improved the efficacy of protectant treatment. In some instances, protectant use was associated with high resistance levels; high insect densities and the highest levels of resistance were recorded from storages in which treated grain was added to old grain residues. We consider good farm hygiene should be practised to slow the development of resistance.