In different parts of the world, aphid populations and their natural enemies are influenced by landscapes and climate. In the Neotropical region, few long-term studies have been conducted, maintaining a gap for comprehension of the effect of meteorological variables on aphid population patterns and their parasitoids in field conditions. This study describes the general patterns of oscillation in cereal winged aphids and their parasitoids, selecting meteorological variables and evaluating their effects on these insects. Aphids exhibit two annual peaks, one in summer–fall transition and the other in winter-spring transition. For parasitoids, the highest annual peak takes place during winter and a second peak occurs in winter–spring transition. Temperature was the principal meteorological regulator of population fluctuation in winged aphids and parasitoids during the year. The favorable temperature range is not the same for aphids and parasitoids. For aphids, temperature increase resulted in population growth, with maximum positive effect at 25°C. Temperature also positively influenced parasitoid populations, but the growth was asymptotic around 20°C. Although rainfall showed no regulatory function on aphid seasonality, it influenced the final number of insects over the year. The response of aphids and parasitoids to temperature has implications for trophic compatibility and regulation of their populations. Such functions should be taken into account in predictive models.

Augmentative biological control is not commonly used in commercial orchards. We used an exclusion system to evaluate the potential of early-season releases of the European earwig (Forficula auricularia L., Dermaptera: Forficulidae) for control of the rosy apple aphid (Dysaphis plantaginea Passerini, Hemiptera: Aphididae) in the spring of 2009 in two pesticide-free apple orchards. In order to conduct this experiment we successfully reared earwigs with a high survival rate of nymphs (more than 96%) which may have commercial application. There were three treatments in the study: (i) a ‘release treatment’ where we confined the released earwigs in the canopy by using a barrier system; (ii) an ‘exclusion treatment’ where we blocked free access of earwigs into the canopy using the same barrier system; and (iii) a ‘control treatment’ that represented the natural situation. Contrary to expectations, earwig releases did not reduce D. plantaginea populations. In general, the abundance of natural enemies and their groups did not differ significantly among treatments, except for earwigs. We observed that the exclusion systems we used successfully kept both earwigs and ants away from tree canopies; total numbers on trees in the ‘exclusion treatment’ were significantly lower than on the other two treatments. Due to the complexity and difficulty of evaluating augmentative releases of natural enemies in open orchard conditions, we conclude that new technical approaches to control site conditions are needed when conducting such studies.

Aphids are among pests of economic importance throughout the world. Together with transmitting plant viruses, aphids are capable of inflicting severe crop production losses. They also excrete honeydew that favours the growth of sooty mold which reduces the quality of vegetables and fruits and hence their market values. Rapid and accurate identification of aphids to the species level is a critical component in effective pest management and plant quarantine systems. Even though morphological taxonomy has made a tremendous impact on species-level identifications, polymorphism, morphological plasticity and immature stages are among the many challenges to accurate identification. In addition, their small size, presence of cryptic species and damaged specimens dictate the need for a strategy that will ensure timely and accurate identification. In this study, polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP)-based on mitochondrial cytochrome c oxidase subunit I gene and DNA barcoding were applied to identify different aphid species collected from different agro-ecological zones of Kenya. Three restriction enzymes RsaI, AluI and Hinf1 produced patterns that allowed unambiguous identification of the species except Aphis craccivora and Aphis fabae. Analyses of the barcode region indicated intraspecific and interspecific sequence divergences of 0.08 and 6.63%, respectively. DNA barcoding identified all species, including the morphologically indistinguishable A. craccivora and A. fabae and separated two subspecies of A. fabae. Based on these results, both PCR-RFLPs and DNA barcoding could provide quick and accurate tools for identification of aphid species within Aphididae subsequently aiding in effective pest management programmes and enhance plant quarantine systems.

To estimate the net effect of climate change on natural populations, we must take into account the positive and negative effects of temperature oscillations and climate variability. Warming because of climate change will likely exceed the physiological optima of tropical insects, which currently live very close to their thermal optima. Tropical insects will be negatively affected if their optima are exceeded otherwise warming may affect them positively. We evaluate the demographic responses of the cowpea aphid, Aphis craccivora, to summer warming in subtropical and tropical Taiwan, and examine the effects of diel temperature oscillation on these responses. Aphids were reared at four temperatures (current summer mean, +1.4, +3.9 and +6.4 °C), the latter three simulating different levels of warming. At each average temperature, aphids experienced constant or oscillating (from −2.9 to +3.6 °C of each mean temperature) regimes. As the simulated summer temperatures increased, so did the negative effects on life-history traits and demographic parameters. Compared with aphids reared in constant temperatures, aphids reared in oscillating temperatures developed more slowly and had a longer mean generation time, but their net reproductive rate was higher. These findings demonstrate that climate warming will affect demographic parameters and life-history traits differentially. Studies that use constant temperatures are unlikely to accurately predict biotic responses to climate change.

In this study, we present cytogenetic data regarding 66 Myzus persicae strains collected in different regions of Italy. Together with the most common 2n = 12 karyotype, the results showed different chromosomal rearrangements: 2n = 12 with A1–3 reciprocal translocation, 2n = 13 with A1–3 reciprocal translocation and A3 fission, 2n = 13 with A3 fission, 2n = 13 with A4 fission, 2n = 14 with X and A3 fissions. A 2n = 12–13 chromosomal mosaicism has also been observed. Chromosomal aberrations (and in particular all strains showing A1–3 reciprocal translocation) are especially frequent in strains collected on tobacco plants, and we suggest that a clastogenic effect of nicotine, further benefited by the holocentric nature of aphid chromosomes, could be at the basis of the observed phenomenon.

Field populations of the cotton aphid, Aphis gossypii Glover, are structured into geographically widespread host races. In the cotton-producing regions of West and Central Africa (WCA), two genotypes have been repeatedly detected within the cotton host race, one of which (Burk1) is prevalent (>90%) and resistant to several insecticides, as opposed to the second one (Ivo). Here, we conducted whole plant and field cage experiments to test hypotheses for such low genetic diversity, including selection from insecticide treatments, interclonal competition and adaptation to host plant, or climatic conditions. To assess the genetic diversity of immigrant aphids, alatae were trapped and collected on cotton and relay host plants (okra and roselle) in the early cropping season. Individuals were genotyped at eight specific microsatellite loci and characterized by a multilocus genotype (MLG). When independently transferred from cotton (Gossypium hirustum L.) leaf discs to whole plants (G. hirsutum and G. arboreum, roselle and okra), Ivo and Burk1 performed equally well. When concurrently transferred from cotton leaf discs to the same plant species, Ivo performed better than Burk1, indicating that competition favoured Ivo. This was also the case on G. hirsutum growing outdoors. Conversely, Burk1 prevailed when cotton plants were sprayed with insecticides. In experiments where aphids were allowed to move to neighbouring plants, Burk1 was better represented than Ivo on low-populated plants, suggesting that dispersal may be a way to avoid competition on crowded plants. Most cotton aphids collected on cotton or relay host plants in the early cropping season were Burk1 (>90%), indicating high dispersal ability and, probably reflecting high frequency on host plants from which they dispersed. In the agricultural landscape of WCA, the use of broad-range insecticides on both cotton and relay host plants has led to the prevalence of one genotype of A. gossypii resistant to different classes of insecticides. Deployment of widespread and integrated pest management strategies are needed to restore cotton aphid control.

To determine whether host body size is the currency used by the aphidiine parasitoid, Lysiphlebus ambiguus Haliday (Hymenoptera: Braconidae), in assessing host quality, the aphid, Aphis fabae Scopoli (Homoptera: Aphididae), was reared at either high or low temperature to yield hosts of the same instar with different body sizes. Cohorts of A. fabae raised at 15°C and 30°C and exposed to individual female L. ambiguus in no-choice tests were successfully parasitized in all host stages from 1st instar nymphs to adults. However, younger and smaller aphids were more susceptible to parasitism than older and larger nymphs or adults, as measured by the number of mummies produced. For aphid cohorts reared at 15°C, the proportion of female progeny, progeny adult size, and development time all increased linearly with aphid size at the time of attack. In contrast, for aphid cohorts raised at 30°C, the proportion of female progeny and progeny adult size declined with aphid size, while development time remained unaffected. Through manipulation of host rearing temperature, we have shown that at cooler temperatures the koinobiont parasitoid, L. ambiguus, responds to host size in the same way as an idiobiont parasitoid, but that this response is compromised at higher temperatures. Our results suggest that differential mortality during development is likely to influence the observed secondary sex ratio in relation to aphid size for aphid cohorts raised at higher temperatures due to disruption of the activity of the host's primary endosymbiont and that such reduced nutritional quality of aphids cannot be compensated by increased development time.

Hop plants were sprayed with (Z)-jasmone, at a rate of 50 g ha−1, during the spring migration of the damson–hop aphid Phorodon humuli (Schrank) in 2002 and 2003. Numbers of P. humuli spring migrants colonizing hop plants, Humulus lupulus L., 2–6 and 7–11 days after applying this treatment were assessed in both years. During the first five-day period, significantly more spring migrants were found on hop plants treated with (Z)-jasmone, in comparison with control plants, in 2002. By contrast, no significant difference was evident in the second five-day period. Although the migration in 2003 was much lighter than in 2002, greater numbers of migrants were again removed from treated plants. Indeed, more spring migrants were removed from plants sprayed with (Z)-jasmone in this year during both five-day periods (11 and 44%, respectively) compared with the 23% greater numbers removed in the first five-day period in 2002. Therefore, unlike some other species of aphid, where numbers were consistently lower on plots sprayed with (Z)-jasmone, spraying the secondary host of P. humuli with this compound appears to increase colonization by spring migrants.

DL-β-aminobutyric acid (BABA) is a non-protein amino acid that is an effective inducer of resistance against a variety of plant pathogens. However, examples of BABA-induced resistance against insect herbivores have not been reported. We applied BABA as a soil drench to legumes and monitored its effects on the pea aphid Acyrthosiphon pisum (Harris). On tic bean (Vicia faba var. minor), BABA increased aphid mortality, caused a reduction in the mean relative growth rate of individual insects and lessened the intrinsic rate of population increase (rm). BABA also caused significant reductions in the growth rate of A. pisum on pea (Pisum sativa), broad bean (Vicia faba var. major), runner bean (Phaseolus coccineus), red clover (Trifolium pratense) and alfalfa (Medicago sativa). No direct toxic effects of BABA against A. pisum were found, and no phytotoxic effects that may have caused a reduction in aphid performance were detected. Possible mechanisms behind this BABA-induced inhibition of aphid performance are discussed.

In this study, we evaluated in field trials the effects on non-target species, of transgenic corn producing the Cry1Ab toxin of Bacillus thuringiensis (Bt). In 1998, we collected Ostrinia nubilalis (Hübner) larvae from transgenic Bt corn (Novartis Hybrid 176) and non-Bt corn at four geographical sites. We found a significant variation in parasitism by the tachinids Lydella thompsoni (Herting) and Pseudoperichaeta nigrolineata (Walker) among sites, and more parasitism in non-Bt than in Bt fields. The Bt effect did not vary significantly among fields. In 1999, we performed a field experiment at two sites, comparing the temporal abundance of non-target arthropods in Bt corn (Monsanto Hybrid MON810) and non-Bt corn. The non-target insects studied included the aphids Metopolophium dirhodum (Walker), Rhopalosiphum padi (L.) and Sitobion avenae (F.), the bug Orius insidiosus (Say), the syrphid Syrphus corollae (Meigen), the ladybird Coccinella septempunctata (L.), the lacewing Chrysoperla carnea (Stephens), thrips and hymenopteran parasitoids. For all species but one, the number of individuals varied greatly over the season but did not differ between the types of corn. The only exception was thrips which, at one site, was significantly more abundant in Bt corn than in non-Bt corn. However this difference did not remain significant when we took the multiple tests into account. Implications for pest resistance management, population dynamics and risk assessment are discussed.

An annual legume cover crop was evaluated in pecan orchards to increase coccinellids that would reduce pecan aphids. Treatments were a ‘Dixie’ crimson clover and hairy vetch mixture and a grass sod. Coccinellids were abundant on the legume ground covers, but coccinellid density in the tree canopy was rarely affected by ground cover treatment. There were substantial differences between the coccinellid species collected from the legumes and from the trees. In Oklahoma, Olla v-nigrum (Mulsant) and Cycloneda munda (Say) were the main species in the trees, while Hippodamia convergens Guerin, Coccinella septempunctata L, and Coleomegilla maculata lengi Timberlake were dominant species in the legumes. In Georgia, Harmonia axyridis (Pallas) was the dominant species in the trees, and C. septempunctata in the legumes. Pecan aphids at two Oklahoma sites usually were not affected by cover crop treatment, but at the Georgia site, early-season aphids frequently were lower with a legume cover crop than with a grass sod. The accumulated effect of all aphid predators and parasitoids attracted to the legume aphids may have reduced the density of the pecan aphid.

The effect of maternal crowding on the offspring sex ratio of a cereal aphid parasitoid Lysiphlebus delhiensis (Subba Rao & Sharma) (Hymenoptera: Braconidae) was examined. Increasing the number of mothers per host-patch always increased the proportion of males in the population (p). The extent of variations in p at different levels of maternal crowding was compared with the prediction of the Hamiltonian LMC model, i.e. p = (n-1)/2n, where n = number of mothers/host-patch. The perception of trace odours of conspecific females induced haploid oviposition. Differential mortality of the larvae by sex in superparasitised hosts, shifting the p towards sons has been discussed. The inversely parasitoid-density-dependent p indicates that for obtaining maximum number of female progeny, the ratio of female parasitoid to the host in mass breeding should not be less than 1:100 at a time.

We evaluated selected cool-season annual and perennial legumes as potential ground covers to supply nitrogen and to increase beneficial arthropod populations in a pecan orchard. Densities of aphids (Homoptera: Aphididae), lady beetles (Coleoptera: Coccinellidae), damsel bug (Hemiptera: Nabidae), green lacewings (Neuroptera: Chrysopidae), brown lacewings (Neuroptera: Hemerobiidae), hover flies (Diptera: Syrphidae), spined soldier bug and other stink bugs (Hemiptera: Pentatomidae), and spiders (Araneida) were monitored at 7–14 day intervals during the growing season for three years. Aboveground biomass production and nitrogen content of the legumes was measured for two years. Aphids peaked during early spring each year, with the highest density usually on ‘Dixie’ crimson clover and ‘Kenland’ red clover. Density of lady beetles was positively correlated with that of aphids, but spider densities were not. Other arthropods usually were not abundant. Nitrogen in the tops of the annual legumes ranged from 20 kg/ha to 89 kg/ha when assessed after a single harvest at anthesis; for the perennial legumes it was from 108 kg/ha to 179 kg/ha following two harvests in June and September. We chose two annual legumes (‘Dixie’ crimson clover and hairy vetch) and two perennial legumes (‘Louisiana S-1’ white clover and ‘Kenland’ red clover) for further evaluation.

Annual legumes and mixtures of annual legumes and grasses can perform several functions as understory cover crops in pecan orchards, such as providing nitrogenrich organic matter to improve soil fertility, or by sustaining lady beetles and other arthropods that may aid the biological control of pecan pests. Remaining questions concern selection of appropriate plant materials; whether to use cover crops singly or in mixtures; how to ensure reseeding as well as a substantial N contribution; whether, when, and how to use mowing and tillage; and fertilization options. Different considerations apply when dealing with cool- vs. warm-season cover crops. With minor adjustments, growers could adapt present cultural practices to include cool-season cover crops. These could be used throughout the orchard, by establishing appropriate self-reseeding species and avoiding both excessive mowing and indiscriminate placement of N-rich fertilizers. Within alleys, alternating 2-m strips of cool-season cover crops could be tilled in mid to late April or allowed to mature. The tilled strips would supply N to pecan trees immediately, whereas the adjoining untilled (remnant) strips could be mowed after seed is mature, to ensure dispersal of seed and reestablishment of cover crops over the entire alley. Cool-season annual legumes that die or are killed in late spring will probably furnish N and other nutrients at a suitable time, particularly in orchards with sprinkler irrigation. Warm-season cover crops, if desired, should be restricted to alleys to reduce possible competition with pecan. Alleys provide better illumination than do tree rows during periods when pecan trees are in leaf, and the tillage mentioned above will encourage emergence of warm-season cover crops. If these die or are killed in late summer or early fall, timing of N release may not be optimal, in the absence of adequate irrigation. Many options and tradeoffs need to be explored before choosing a cover-crop system. Attimes, several objectives may appear to conflict, and even delicately-managed mixtures of species may not fulfill all the desired functions.