Small Aphid Research Articles

Developing a hybrid convolutional neural network for automatic aphid counting in sugar beet fields

Aphids can cause direct damage and indirect virus transmission to crops. Timely monitoring and control of their populations are thus critical. However, the manual counting of aphids, which is the most common practice, is labor-intensive and time-consuming. Additionally, two of the biggest challenges in aphid counting are that aphids are small objects and their density distributions are varied in different areas of the field. To address these challenges, we proposed a hybrid automatic aphid counting network architecture which integrates the detection network and the density map estimation network. When the distribution density of aphids is low, it utilizes an improved Yolov5 to count aphids. Conversely, when the distribution density of aphids is high, it switches to CSRNet to count aphids. To the best of our knowledge, this is the first framework integrating the detection network and the density map estimation network for counting tasks. Through comparison experiments of counting aphids, it verified that our proposed approach outperforms all other methods in counting aphids. It achieved the lowest MAE and RMSE values for both the standard and high-density aphid datasets: 2.93 and 4.01 (standard), and 34.19 and 38.66 (high-density), respectively. Moreover, the AP of the improved Yolov5 is 5 % higher than that of the original Yolov5. Especially for extremely small aphids and densely distributed aphids, the detection performance of the improved Yolov5 is significantly better than the original Yolov5. This work provides an effective early warning caused by aphids in sugar beet fields, offering protection for sugar beet growth and ensuring sugar beet yield. The datasets and project code are released at: https://github.com/JunfengGaolab/Counting-Aphids.

Taxonomy and Phylogeny of the Aphid Genus Nippolachnus Matsumura, 1917, with Synonymy of the Mysterious Neonippolachnus Shinji, 1924 (Hemiptera: Aphididae: Lachninae).

Nippolachnus Matsumura, 1917 is a small aphid genus from the tribe Tuberolachnini (Hemiptera: Lachninae) occurring in Southeast Asia. Species from this genus are quite characteristic and stand out among lachnids for their morphology and ecological associations. We have performed a revision and phylogenetic analyses to elucidate the relationships within Nippolachnus and other representatives of Tuberolachnini. Here, the taxonomy of the genus is revised based on morphological data to include seven species, three of them newly described: Nippolachnus chakrabartiisp. nov. from India, Nippolachnus sinensissp. nov. from China, and Nippolachnus malayaensissp. nov. from Indonesia. Nippolachnus appear to be non monophyletic genus and a new genus, Indolachnusgen. nov., is described to accommodate Nippolachnus himalayensis (van der Goot, 1917) as Indolachnus himalayensis (van der Goot, 1917) comb. nov. The new genus is a sister group to the remaining Nippolachnus species, which created a monophyletic clade. Neonippolachnus Shinji, 1924 syn. nov. is recognised as a synonym of Nippolachnus, and Neonippolachnus betulae Shinji, 1924 syn. nov. as a synonym of Nippolachnus micromeli Shinji, 1924. For the first time, a scanning electron microscopy study of the sexual generation of N. piri Matsumura, 1917 has been performed. Apterous and alate viviparous females of N. bengalensis Basu and Hille Ris Lambers, 1968, N. piri, and N. micromeli, and alate viviparous females of N. xitianmushanus Zhang and Zhong, 1982 are re-described and illustrated, as well as apterous and alate viviparous females of I. himalayensiscomb. nov. Hitherto unknown morphs of N. micromeli, N. piri, and N. xitianmushanus are described. A lectotype and paralectotypes of N. xitianmushanus are designated herein. Notes on distribution and host plants are given, and keys to apterous and alate viviparous females of the genera Nippolachnus and Indolachnus are also provided.

Evaluating a new aphid biocontrol agent: The role of aphid density in modulating oviposition behaviour in the American hoverfly, Eupeodes americanus, and the aphid midge, Aphidoletes aphidimyza

AbstractHoverfly larvae are voracious predators of aphids but have limited dispersal capacity, so their survival depends critically on female selection of oviposition sites. For aphid control purposes, the ability of females to find small aphid colonies is especially valuable. In this study, the oviposition strategy and minimum aphid density triggering the oviposition of the American hoverfly, Eupeodes americanus (Wiedemann, 1830) (Diptera: Syrphidae), was compared with that of the aphid midge, Aphidoletes aphidimyza (Rondani, 1847) (Diptera: Cecidomyiidae), a predator commercially available in Canada as a reference. Oviposition behaviour was evaluated at densities of 0, 2, 5, 10, and 50 aphids per plant. This was tested on two economically significant plant/aphid systems: pepper plants infested by the green peach aphid, Myzus persicae (Sulzer 1776) (Hemiptera: Aphididae), and cucumber plants infested with the melon aphid, Aphis gossypii Glover 1877. Results showed that both predators lay their eggs in proportion to the size of the colony of aphids. Oviposition by E. americanus required a minimum density of 5 aphids on cucumber but only 2 on pepper, whereas for A. aphidimyza, it was also 5 aphids on cucumber, but 10 on pepper. The hoverfly laid more than twice as many eggs as A. aphidimyza on pepper. It also laid more eggs on pepper than on cucumber and the pattern is the opposite for A. aphidimyza. Therefore, the identity of the aphid‐host plant complex appears to modulate the oviposition of these predators. This study demonstrates the ability of E. americanus to respond to lower densities of aphids than A. aphidimyza early in the infestation on sweet pepper plants and shows that its oviposition rate is at least as effective as A. aphidimyza on cucumber. Consequently, these attributes of its oviposition behaviour indicate that E. americanus has great potential for use as an aphid biocontrol agent in these crops.

A method for DNA extraction and molecular identification of Aphids

Aphid species (Insecta, Hemiptera) are economically important invasive pest throughout the world, though their identification is intricate due to tiny size and inconspicuous nature of morphology. Mitochondrial cytochrome c oxidase I (mtCOI) region has been proven to be a standard barcode to identify the diverse array of insect groups. Isolation of good quality DNA is a fundamental first step in insect DNA barcoding which is obtained by standardizing the DNA isolation method. In this study, we demonstrate a modified CTAB method for the isolation of DNA to maximize the quality and yield from small aphids. This method will help the researchers to efficiently isolate DNA from small aphid and the method can be utilized for other small insects as well. We evaluated the quality of the isolated DNA and the mtCOI gene region were subjected to PCR amplification. Further, the gene segment was sequenced and gene annotation was done by NCBI BLAST program through which the insect was found to be Aphis gossypii. This study provides a set of molecular tools that can be used for identification of insect at species level through DNA barcoding and biodiversity analysis.•Detailed method to maximize quality and quantity of genomic DNA isolated from aphids.•Molecular identification of aphids using mtCOI gene amplification and sequence validation.•First report on Aphis gossypii infecting Solanum trilobatum provides insights of pest identification and management.

Ceviz yaprakbitleri (Chromaphis juglandicola (Goeze) (Hemiptera: Callaphididae) ve Panaphis juglandis (Goeze) (Hemiptera:Callaphididae)) ile Beslenen Chrysoperla carnea (Stephen) (Neuroptera: Chrysopidae)‘nın Popülasyon Parametrelerinin Belirlenmesi

Ceviz küçük yaprakbiti (Chromaphis juglandicola (Kalt.) (Hem.:Aphididae) ve ceviz yeşil yaprakbiti (Panaphis juglandis) (Goeze) (Hemiptera: Callaphididae) Van gölü havzasındaki önemli ceviz zararlılarıdır. Ceviz yaprağının alt ve üst kısmında ayrı kolonize olan yaprakbitleri, popülasyonlarının yoğun olması durumunda ceviz de kalite ve kantite kayıplarına neden olurlar. Bu çalışmada, zararlıların biyolojik mücadelesine yönelik, en önemli avcılarından biri olan Chrysoperla carnea (Stephen) (Neuroptera: Chrysopidae)‘nın her iki yaprakbiti ile beslenmesine dayalı popülasyon büyüme oranı parametreleri belirlenmiştir. Denemeler 25±10°C, %65±5 nem ve 16:8 (L:D) h (5.000 lüks) ışıklanma süresi koşullarındaki iklim odalarında gerçekleştirilmiştir. Yaşam çizelgesi parametreleri yaş ve döneme bağlı iki eşeyli yaşam çizelgesi yöntemine göre hesaplanmıştır. Chromaphis juglandicola ve Panaphis juglandis ile beslenen C. carnea‘nın kalıtsal üreme yeteneği (r), Üreme gücü sınırı (λ), net üreme gücü (R0) ve ortalama döl süresi (T) sırasıyla 0,082 gün-1, 1,082 gün-1, 59,47 yumurta/generasyon ve 49,76 gün, olarak belirlenmiştir. Bulguların C. carnea tarafından Panaphis juglandis ve Chromaphis juglandicola'nın biyo-kontrollerindeki olası etkileri tartışılmıştır. Elde edilen sonuçlar yaprakbitleri için hazırlanacak mücadele programlarında kullanılabilecektir.

Predation rate linked to life table of Chrysoperla carnea (Stephen) (Neuroptera: Chrysopidae) fed on small walnut aphid (Chromaphis juglandicola) (Kalt.) (Hemiptera: Aphididae): with population and predation projections

Small walnut aphid (Chromaphis juglandicola (Kaltenbach) (Hemiptera: Aphididae) is important pest in walnut orchards in Lake Van Basin, Turkey. In this study, the life-table parameters reflecting population growth rate and predation rate of Chrysoperla carnea (Stephen) (Neuroptera: Chrysopidae), which is one of the important predators of the pest, were determined. Life table parameters were estimated according to age-stage, two-sex life table method. Variances and standart errors of population parameters were obtained according to Bootstrap method. The values obtained for the intrinsic rate of increase (r), finite rate of increase (λ), net reproductive rate (R0) and mean generation time (T) were 0.072 d−1, 1.070 d−1, 62.48 offspring and 57.16 d, respectively of C. carnea fed on Chromaphis juglandicola. The net predation rate (C0) was determined as 212.9 aphids. Pradation projection was performed by using timing program to prevent the predator’s decrease in predation capacity and to determine the most appropriate release quantities and the appropriate interval between releases (to fill predation gaps) for biological control. The possible effects of the findings on the bio-controls of Chromaphis juglandicola by C. carnea were discussed. Results obtained can be used in pest management program that will be prepared for this pest.

Foraging and Daily Activity Features of Ants of the Genus Formica (Insecta, Hymenoptera) in Forest–Steppe Biotopes of Saratov Oblast

This paper presents the results of our research on the foraging activity of ants in forest–steppe biotopes of Saratov oblast. The food spectrum of ants was found to include small invertebrates (mainly insects), plant seeds, and aphid honeydew. Ants are able to switch to the most massive type of food. F. pratensis behaves as a species with a daytime or morning–evening activity type, depending on the weather conditions. F. rufa is a species with a daily activity type.

A coarse-to-fine network for aphid recognition and detection in the field

In agriculture, aphids are one of the most destructive pests, responsible for major reductions in wheat, corn and rape production leading to significant economic losses. However, manual pest recognition approaches are often time-consuming and laborious for Integrated Pest Management (IPM). In addition, the existing pest detection methods based on Convolutional Neural Network (CNN) are not satisfactory for small aphid recognition and detection in the field because aphids are tiny and often in dense distributions. In this work, a two-stage aphid detector named Coarse-to-Fine Network (CFN) is proposed to address these problems. The key idea of our method is to develop a Coarse Convolutional Neural Network (CCNN) for aphid clique searching as well as a Fine Convolutional Neural Network (FCNN) for refining the regions of aphids in the clique. Specifically, The CCNN detects approximately all the object regions from natural aphid images with various aphid distributions including dense aphid cliques and sparse aphid objects, in which an Improved Non-Maximum Suppression (INMS) strategy is proposed to eliminate overlapping regions. Then, the FCNN further refines the detected aphid regions from the CCNN. The final recognition and detection result would be obtained by combining the outputs from CCNN and FCNN together. Experiments on our dataset show that our CFN achieves an aphid detection performance of 76.8% Average Precision (AP), which improves 20.9%, 18%,13.7% and 12.5% compared to four state-of-the-art approaches.

First record of Aphis citricola van der Goot (Homoptera: Aphididae) on citrus in Southern Greece

The green citrus aphid, Aphis citricola van der Goot, known also as spiraea aphid, Aphis spiraecola Patch, was first noticed in an orange grove, cv Washington Navel, in Korinthia southern Greece during spring 1986. It was collected from tender shoots as early as about mid March and was also found in large numbers in samples taken during April and May and in lesser numbers in October and November of the same year. It was also collected from clementine trees during May. During 1987 this species was also present in samples taken from another orange grove, cv Washington navel, located in the Co. Korinthia as well. It was found later in the season, in May, as compared with the previous year. That was due to the snow and the extremely cold weather that occurred during March, which resulted in the destruction of young growth and hence in the delay of the aphid appearance. A. citricola has been previously recorded in Greece on Matricaria chamomilla L., Crataegus pyracantha Pers. and Solanum tuberosum L., on Zinnia elegans.Jacq. and on Prunus armeniaca L. and Pimpinella anisum L. A. citricola is a small aphid with 1.2-2.2 min length and body yellowish green to apple green. Siphunculi and cauda are dark brown and the head is brown in apterac. It is very similar to Aphis pomi De Geer and is often confused with it in the literature, especially on Rosaceae. A. pomi has lateral tubercles on abdominal segments 2-4, rarely fewer than 14 hairs on cauda and length of the last rostral segment more than 130µm. A. citricola has no lateral tubercles on abdominal segments 2-4, usually fewer than 12 hairs on cauda, and last rostra] segment less than 120µm in length. One more difference concerns the shape of the cauda which is more elongate and visibly notched at base in A. citricola than in A. poini. A. citricola causes curling and distortion of the leaves, especially of those near apices of tender shoots of the host plants. This is very characteristic in certain citrus such as orange and clementine trees. It is a highly polyphagus species that occurs on hosts belonging to more than 20 families, including Amaranthaccae, Caprifoliaccae, Compositae, Euphorbiaccac, Rosaccae, Rubiaccae, Rutaceae, Urticaceae and Verbenaceac but is of particular importance on citrus. A. citricola is considered the most harmful aphid species for orange, mandarins and clementine trees in Italy and in other citrus growing countries of the Mediterranean basin. This species was known in North America at least since 1907 and was introduced to the Mediterranean region in about 1931. A. citricola appeared in citrus groves in Mediterranean countries almost 20 years ago, while it was first recorded in Israel in 1970 and became a major pest in citrus groves in 1973. It is a vector of citrus tristeza virus but its ability for transmitting this virus is much lower than that of Toxoptera citricidus (Kirkaldy). A. citricola may reproduce either anholocyclically or holocyclically. Anholocyclic reproduction occurs in many parts of the world and is considered as more frequent. Nevertheless, holocyclic reproduction also occurs, and in this case, the genus Spiraea of Rosaccae is the primary host, although oviposition may take place on the same citrus trees in Japan. The intrinsic rate of natural increase of the aphid attained its maximum at a constant temperature near 27°C. The numbers of A. citricola found in the samples from cv Washington navel were large and higher than those of Toxoptera aurantii (Boyer de Fonscolombe), when the latter species was present. With the assumption that such large numbers occur also in other areas of the country, A. citricola should be the dominant and most harmful aphid species on citrus in Greece, as this is the case in other Mediterranean countries.

Resource partitioning in a ladybird, Menochilus sexmaculatus: function of body size and prey density.

In the present study, resource partitioning by natural conspecific size variants (small and large) of ladybird, Menochilus sexmaculatus (Fabricius) females, in response to varying prey densities was assessed using functional and numerical responses as measures of prey density. The prey provided was small (second) and large (fourth) instars of Aphis craccivora Koch. Results revealed that under choice condition, small and large females of M. sexmaculatus consumed higher number of small and large instars, respectively. Small females exhibited a modified Type II functional response on small aphid instars and a Type II functional response on fourth aphid instars. Large females exhibited a Type II functional response when provided either second or fourth aphid instars. Numerical response in terms of numbers of eggs laid by both the females increased with increase in the density of either of the aphid instars. However, in small females, oviposition had a positive correlation with the numbers of small and large aphid instars consumed; being strong for the small aphid instars. While in large females, oviposition was positively correlated with the numbers of large aphid instars consumed and not small aphid instars. It therefore seems that intraspecific resource partitioning in M. sexmaculatus occurs prominently in large females than the small females.

Antibiosis in wheat interacts with crowding stress to affect Metopolophium dirhodum development and susceptibility to malathion

AbstractWe used a laboratory study to compare the performance of rose‐grain aphid, Metopolophium dirhodum (Walker) (Hemiptera: Aphididae), on the wheat cultivars ‘Huntsman’ (susceptible) and ‘Rapier’ (partially resistant) in both low density (uncrowded) and high density (crowded) colonies and examined the consequences for aphid susceptibility to malathion. Adult apterae that developed on Rapier wheat had their mean relative growth rate (MRGR) reduced by 6 and 9% under uncrowded and crowded conditions, respectively, whereas the crowding treatment reduced MRGR by 3%, but only in Rapier aphids. Rapier resistance also reduced adult dry weight by 13 and 14% under crowded and uncrowded conditions, respectively, whereas crowding reduced it by 34 and 35% in Rapier and Huntsman aphids, respectively. Development on Rapier substantially reduced the topical LC50 of malathion by 37.8 and 34.8% under crowded and uncrowded conditions, suggesting that plant antibiosis increased malathion susceptibility. By comparison, crowding only reduced the LC50 by 29.5 and 26.0% on Huntsman and Rapier. The LD50 data showed that reductions on aphid body size on Rapier and through crowding did not fully explain the differences in LC50. This was particularly in the values for crowded aphids that were actually 80% higher than for uncrowded ones. This apparent tolerance of crowded aphids, however, may partly be due to loss of insecticide from small aphids at dosing. Evidence of synergy between plant resistance and insecticide susceptibility raises the possibility of using reduced concentrations of pesticides to control aphids on resistant crop cultivars, with diminished impacts on non‐target and beneficial species important in integrated pest management (IPM) programs.

A comparative study of the sexual morphs and the life cycles of the palaearctic species of Glyphina Koch, 1865 (Hemiptera: Aphididae: Thelaxinae)

Glyphina is a small aphid genus with three palaearctic and two nearctic species associated with Betulaceae, the sexual morphs and life cycles of which are little known. Detailed descriptions and illustrations are provided of the oviparous females and males of the three palaearctic species: Glyphina betulae (Linnaeus, 1758), Glyphina jacutensis Mordvilko, 1931 and Glyphina pseudoschrankianaBlackman, 1989. G. pseudoschrankiana has been for the first time recorded from Katowice, Poland. Keys for their identification are provided, and additional data about biology, life cycle and the damage caused by these insects are presented.

Temperature Influences the Handling Efficiency of an Aphid Parasitoid Through Body Size-Mediated Effects

It is well known that increasing the ambient temperature increases the metabolic rate and consequently, the foraging rate of most insects. However, temperature experienced during the immature stages of insects affects their adult size (an inverse relationship). Because body size is generally correlated to foraging success, we hypothesized that temperature indirectly influences the foraging efficiency of adult insects through developmental effects. We first investigated the role of parasitoid: host body size ratio on the handling time of Aphidius colemani (Viereck) (Hymenoptera: Braconidae), then tested the prediction that increasing temperature during immature development increases the handling time of adults. As expected, parasitoids took longer to handle large aphids than small aphids. However, large parasitoids did not have shorter handling times than small parasitoids except when attacking large (adult) aphids. Developmental temperature had the predicted effect on parasitoids: Individuals reared at 25°C were smaller than those insects reared at 15°C. Parasitoids reared at 15°C had similar short handling times for both first instar and adult aphids, whereas parasitoids reared at 25°C took longer to handle adult aphids than first instar aphids. The size-mediated effect of temperature through development on parasitoid efficiency was opposite to the more familiar direct effect of temperature through metabolic rate. We conclude that the net effect of temperature on foraging insects will depend on its relative influence on immature and adult stages.

Extrafloral nectaries indirectly protect small aphid colonies via ant-mediated interactions

When ant-tended aphids parasitize plants with extrafloral nectaries (EFNs), ant-mediated indirect interactions occur between the plants and aphids. In particular, when an aphid colony is small, the honeydew production of the colony is insufficient to attract ants, although EFNs can attract many ants. Under this condition, we asked whether a small aphid colony would gain indirect benefits from EFNs because ants would be attracted by the EFNs instead of the aphids, or whether the aphid colony would suffer strong predatory pressure from ants and/or other predators. To clarify the aphid-plant interactions, the protective services provided by two ant species, Lasius japonicus and Tetramorium tsushimae, for the survival of a small colony of Aphis craccivora were examined on the host plant, Vicia faba, with and without EFNs. More workers of both ant species were recruited to the plants with EFNs than to those without EFNs, and the larvae of a predatory ladybird beetle, Coccinella septempunctata, stayed for a shorter time and preyed on a smaller number of aphids on the plants with EFNs than on those without EFNs. In addition, no negative effects of EFNs, such as predation of the aphids by the ants, were found. Consequently, it is suggested that a small aphid colony gains indirect benefits from the EFNs of its host plant.

Weighty matters: Body size, diet and specialization in aphidophagous ladybird beetles (Coleoptera: Coccinellidae)

Aphidophagous ladybirds exhibit a broad range of body sizes. Until now this has been thought to be a function of the different prey densities that they feed at, with smaller ladybirds feeding at lower prey densities. The size of the prey species they feed on has been considered to have no relationship with ladybird body size. However, these arguments possess a limited capacity to explain observed data from the field. I here demonstrate a more realistic, complex approach incorporating both prey density and the size of prey species. Small ladybirds can feed on small aphids at both low and high densities. However when the aphid species is large they cannot catch the older, bigger, more energy-rich aphid instars due to their small size. They are thus unable to feed on large aphid prey at low densities, although at higher densities numbers of the smaller instars may be sufficient to sustain them. By contrast large ladybirds can feed on large aphids at both low and high densities due to their superior ability to catch the bigger, more energy-rich older aphids; however they cannot be sustained by low densities of small aphids due to food limitation consequent on their large size. This more complex association between ladybird size, prey size and prey density possesses a better explanatory power for earlier field data. Because of this relationship, ladybird body size also provides an important trade-off determining dietary breadth and specialization in the aphidophagous Coccinellidae. Dietary specialists more closely match the size of their limited prey species, have higher overall capture efficiencies and can thus continue to reproduce at lower aphid densities for longer. By contrast dietary generalists adopt a one-size-fits-all strategy, are medium-sized and have lower capture efficiencies of individual prey species, thus requiring higher aphid densities. The role of body-size in dietary specialization is supported by data from the British fauna. Rather than trade-offs related to prey chemistry, which have hitherto been the centre of attention, body size trade-offs are the likely most important universal factor underlying dietary specialization in aphidophagous coccinellids.

Morphological and ecological traits promoting aphid colonization of the Hawaiian Islands

Species introductions into novel habitats, especially island ecosystems, can have devastating effects on ecosystem function and stability. Though none are native, at least 96 aphid species can now be found on one or more of the Hawaiian Islands. As aphids cause direct feeding damage and transmit plant viruses, it is important to identify the traits that have enabled these particular species to successfully colonize the archipelago. To address this question, nine morphological and ecological traits that may contribute to successful colonization were assessed for aphids present in Hawaii. As a comparative null model, we assessed the same traits for heterospecific congeners which are not present in the archipelago, but are present elsewhere in the world. Here we report that traits with higher frequencies among colonizing aphid species are: small apterae size, broad host range, anholocycly (i.e., permanent parthenogenesis), and presence in continental USA. Small aphids arriving from the mainland US and capable of feeding on numerous plant species may be intercepted less often by plant protection agents. It is also likely that asexually reproducing species are well suited to the Hawaiian subtropical climate, thereby eliminating the need for sexual phases and egg-laying for overwintering. By understanding the traits that enable aphids to successfully colonize remote islands, it is our hope that plant protection efforts may be enhanced, thereby reducing damage to native ecosystems.

Consumption of Cinara spp. (Hemiptera, Aphididae) by Cycloneda sanguinea (Linnaeus, 1763) and Hippodamia convergens Guérin-Méneville, 1842 (Coleoptera, Coccinellidae)

Adults and larvae of coccinellids were observed feeding on populations of the giant conifer aphids Cinara spp. on Pinus spp., in Southern Brazil. The objective of this research is to evaluate the consumption capacity of Cycloneda sanguinea (Linnaeus, 1763) and Hippodamia convergens Guerin-Meneville, 1842 (Coleoptera, Coccinellidae) on these aphid species, in order to obtain information for biological control programs. Ten larvae of each predator species were fed with aphids of small size (nymphs of 1st and 2nd instars), and 10 with aphids of medium size (nymphs of 3rd and 4th instars), maintained under 15oC, 20oC and 25oC, 12 h photophase and 70 ± 10% relative humidity. The aphids were counted every 24 hours, replacing those that were consumed. The total consumption of Cinara by the larvae of C. sanguinea was not statistically different at the three temperatures: 325.5; 322.2 and 324.8 of small aphids and 121.3; 140.4 and 109.9 of medium ones, respectively at 15oC, 20oC and 25oC. The consumption by H. convergens was higher than by C. sanguinea and increased noticeably with temperature: 444 aphids at 15oC; 491.3 at 20oC and 513.3 at 25oC, considering the small aphids, and 187.1; 205.1 and 216.6 of medium aphids at the three temperatures. The small aphids weigh about half as much as medium ones and were preferred by all larval instars probably because they are easier to manipulate than the large ones. Both predators, especially the 4th instar larvae, showed high consumption capacity on the Cinara nymphs at all temperatures and can be regarded as promising biological control agents.

Development and consumption capacity of Chrysoperla externa (Hagen) (Neuroptera, Chrysopidae) fed with Cinara spp. (Hemiptera, Aphididae) under three temperatures

The giant conifer aphids Cinara pinivora (Wilson, 1919) and Cinara atlantica (Wilson, 1919) (Hemiptera: Aphididae) are pests on Pinus spp. (Pinaceae) in the South and Southeast regions of Brazil. Larvae of Chrysoperla externa (Hagen, 1861) (Neuroptera, Chrysopidae) were observed feeding voraciously on these aphid colonies. In order to evaluate their potential as biological control agents, some biological parameters and their consumption capacity were studied in laboratory. Ten larvae were isolated in plastic vials and fed with aphids of small size (nymphs of 1st and 2nd instars) and 10 with aphids of medium size (nymphs of 3rd and 4th instars), maintained at 15ºC, 20ºC and 25ºC, under 12:12 h photoperiod and 70 ± 10% RH, and observed daily. The egg incubation period was nine days at 20ºC and four days at 25ºC. The mean larval development period for C. externa was 59.5 days; 22.3 days and 10.9 days, respectively at 15ºC, 20ºC and 25ºC. The pupal stage last 23.2 at 20ºC and 11.1 days at 25ºC. Unfortunately, data of egg and pupal development at 15ºC are not available because the rearing chamber overheated. The mortality rate from egg to adult was 46.2% 46.6% and 20.2% at 15ºC, 20ºC and 25ºC, respectively. The average aphid consumption of each C. externa larva to complete its development was 499.1; 341.7 and 215.1 small aphids, and 126.4; 105.6 and 67.0 medium aphids, at 15ºC, 20ºC and 25ºC, respectively. About 80% of the total food consumption was by the 3rd instar larvae. Although the development was faster and viability higher at 25ºC than at the other two temperatures, the consumption was the highest at 15ºC because the larval period was much longer. Therefore, the larvae of C. externa can be regarded as potential biological control agents of Cinara spp. throughout the year and even in cool areas of Southern Brazil during some periods o the year.

The impact of individual ladybirds (Coccinella septempunctata, Coleoptera: Coccinellidae) on aphid colonies

Pea aphids (Acyrthosiphon pisum) have been reported to produce winged offspring in the presence of predatory ladybirds. These offspring may leave host plants by flight after they have developed into winged adults. The inter-generational nature of this response raises the question about the chances of survival of aphids developing in attacked colonies. We studied the behaviour of predatory ladybirds on host plants by releasing adult 7-spot ladybirds (Coccinella septempunctata) on bean plants hosting either no prey individuals or colonies of 10 or 30 pea aphids. Interactions between predator and prey were recorded until the ladybird left the plant. Ladybird patch residence time increased with the number of aphids present on a plant but beetles generally left a plant before all aphids were eaten. The time budget of the ladybirds revealed a high proportion of time not spent in feeding activities. Predation rate was about one aphid killed per 10min residence time in both treatments with aphid-infested plants. Aphids that survived an attack by the predator or that were alarmed when a conspecific was attacked often emigrated from the host plant, and their number was of the same magnitude as the number of aphids killed by the predator. On average, pea aphid numbers at the end of an experiment were reduced to less than a third of the initial value. The results of the experiment show that attack by single ladybirds does on average not cause immediate extinction of small aphid colonies. The short patch residence times of on average less than two hours show that a predator individual that induces winged-offspring production in an aphid colony will not any longer be present in the colony when the induced offspring mature. To understand the adaptiveness of predator-induced wing development in pea aphids the probabilities of subsequent attacks on an aphid colony need to be investigated.

Rate of spread of PVYn by alateMyzus persicae (Sulzer) from infected to healthy plants under laboratory conditions

Alate green peach aphids,Myzus persicae (Sulzer), tested in a flight chamber during their maiden flight period displayed behaviours ranging from repeated trivial flights to settling on the plants. The interaction of alate vector density and PVYn spread was dichotomous, virus spread was significantly related to vector density in some trials but virus spread was nil or limited and not significantly dependent on vector density in others. The green peach aphid colony used in these experiments provided a mixture of active and highly active alate populations. Results suggest that inactive and active vectors came from the active and highly active alate populations, respectively. Therefore, winged aphids within a species cannot all be attributed the same vector efficiency unless known to originate from the same population. At a 15% inoculum level the intercept for the regression model for the spread of PVYn was 5.03% indicating that there is a significant probability of propagation at aphid densities as low as one. However, over the range of aphid densities tested, the rate of spread per aphid was low, 0.08%, suggesting that reinfection of newly infected plants or movement interference between aphid vectors rapidly became important factors negatively affecting virus spread. Although these results cannot be directly transferred to field conditions they provide confirmation that lowM. persicae numbers can transmit unacceptable levels of mosaic and that low inoculum levels are required to decrease the risk of transmission by the small aphid numbers which cannot be realistically controlled.