This review examines the direct effects of climate change on insect herbivores. Temperature is identified as the dominant abiotic factor directly affecting herbivorous insects. There is little evidence of any direct effects of CO2 or UVB. Direct impacts of precipitation have been largely neglected in current research on climate change. Temperature directly affects development, survival, range and abundance. Species with a large geographical range will tend to be less affected. The main effect of temperature in temperate regions is to influence winter survival; at more northerly latitudes, higher temperatures extend the summer season, increasing the available thermal budget for growth and reproduction. Photoperiod is the dominant cue for the seasonal synchrony of temperate insects, but their thermal requirements may differ at different times of year. Interactions between photoperiod and temperature determine phenology; the two factors do not necessarily operate in tandem. Insect herbivores show a number of distinct life-history strategies to exploit plants with different growth forms and strategies, which will be differentially affected by climate warming. There are still many challenges facing biologists in predicting and monitoring the impacts of climate change. Future research needs to consider insect herbivore phenotypic and genotypic flexibility, their responses to global change parameters operating in concert, and awareness that some patterns may only become apparent in the longer term.

http://www.discoverlife.org/pa/or/polistes/pr/2010nsf_macro/references/Bale_et_al2002.pdf

Herbivory in global climate change research: direct effects of rising temperature on insect herbivores

Publisher Summary A great deal is known concerning the qualitative nutritional requirements of insects. The quantitative aspects of insect nutrition have, however, received less attention, and there have been few studies on the rates of intake and the efficiency of food utilization. In particular, relatively little is known concerning the intake, digestibility and efficiency of conversion of defined diets. Quantitative work with artificial diets has usually involved only measurements of the amount of a particular nutrient required per unit of diet. Insects as a group feed upon a remarkably diverse list of organic substances. At the same time most species show a high degree of specificity in their choice of food. It seems apparent that adaptive nutritional differences must be sought on a quantitative level and that a meaningful comparative nutrition of insects will not emerge until quantitative studies are emphasized. The determination of absolute requirements for dietary constituents depends upon the measurement of intake. Differences in food efficiency can be demonstrated only by measuring intake and growth. Digestibility should also be measured since it can be expected to vary widely with different foods. The efficiency with which digested food is used for growth will vary not only with the maintenance requirement for energy but also with the balance of nutrients.

The Consumption and Utilization of Food by Insects

A suction trap has been made in which the spores entering a narrow orifice, directed into the wind, are impacted on a Vaseline-coated microscope slide moved across the orifice at 2 mm./hr. Estimates of spore content of the air can be made, with higher efficiency than by previous traps, at different times of day and thus be more closely correlated with variations in weather.

Wind-tunnel tests with spores of Lycopodium clavatum showed maximal and minimal efficiencies of 93.8 and 62.4% respectively, with a suction rate of 10.0 1./min., in the range of wind speeds from 1.5 to 9.3 m./sec.

An automatic volumetric spore trap

Dispersal costs can be classified into energetic, time, risk and opportunity costs and may be levied directly or deferred during departure, transfer and settlement. They may equally be incurred during life stages before the actual dispersal event through investments in special morphologies. Because costs will eventually determine the performance of dispersing individuals and the evolution of dispersal, we here provide an extensive review on the different cost types that occur during dispersal in a wide array of organisms, ranging from micro-organisms to plants, invertebrates and vertebrates. In general, costs of transfer have been more widely documented in actively dispersing organisms, in contrast to a greater focus on costs during departure and settlement in plants and animals with a passive transfer phase. Costs related to the development of specific dispersal attributes appear to be much more prominent than previously accepted. Because costs induce trade-offs, they give rise to covariation between dispersal and other life-history traits at different scales of organismal organisation. The consequences of (i) the presence and magnitude of different costs during different phases of the dispersal process, and (ii) their internal organisation through covariation with other life-history traits, are synthesised with respect to potential consequences for species conservation and the need for development of a new generation of spatial simulation models.

Costs of dispersal

Some of the most striking and extreme consequences of rapid, long-distance aerial dispersal involve pathogens of crop plants. Long-distance dispersal of fungal spores by the wind can spread plant diseases across and even between continents and reestablish diseases in areas where host plants are seasonally absent. For such epidemics to occur, hosts that are susceptible to the same pathogen genotypes must be grown over wide areas, as is the case with many modern crops. The strongly stochastic nature of long-distance dispersal causes founder effects in pathogen populations, such that the genotypes that cause epidemics in new territories or on cultivars with previously effective resistance genes may be atypical. Similar but less extreme population dynamics may arise from long-distance aerial dispersal of other organisms, including plants, viruses, and fungal pathogens of humans.

https://science.sciencemag.org/content/sci/297/5581/537.full.pdf

Aerial Dispersal of Pathogens on the Global and Continental Scales and Its Impact on Plant Disease

Physiological factors in insect migration by flight

COFFEE leaf rust (Hemileia vastatrix Berk. and Br.), for long widespread in Asia and Africa, can devastate crops of Coffea arabica. The fungus spread rapidly in West Africa between 1952 and 19621,2, but the New World seemed free from it until 1970 when it was found scattered over a wide area in Bahia, Brazil, where its consequences may be serious3,4. Indeed, in an attempt to protect the valuable crop farther south, a quarantine belt is being established 500 miles long and 30 miles wide from Rio de Janeiro to beyond Bello Horizonte in which all coffee trees are being destroyed.

Possible Wind Transport of Coffee Leaf Rust across the Atlantic Ocean

The maintenance of high atmospheric humidities for entomological work with glycerol-water mixtures

Small suction traps for estimating the density of airborne insects, and its fluctuations, in relatively sheltered situations, e.g. in crops, have already been designed and used.

Larger, more powerful traps have now been developed for use in more exposed situations where insect densities are very low, or where winds are relatively strong, e.g. high in the air. Because of the large sample obtained they also enable very short-term density fluctuations to be followed.

The radical modifications of design and the special problems encountered in the operation of very large traps are described.

The development of large suction traps for airborne insects

This paper describes the design and operation of a suction trap which takes in air at a constant rate in winds up to 12 m.p.h. The catch is deposited in a collecting tube into which closely fitting disks fall, one every hour, thus segregating the catch into successive hourly samples. The trap is electrically driven; it operates in all weathers and heavy rain does not disorganize the catch.

C. G. Johnson

Papers

Physiological factors in insect migration by flight

Possible Wind Transport of Coffee Leaf Rust across the Atlantic Ocean

The maintenance of high atmospheric humidities for entomological work with glycerol-water mixtures

The development of large suction traps for airborne insects

A suction trap for small airborne insects which automatically segregates the catch into successive hourly samples