Lack of kin discrimination in the eusocial aphid pseudoregmabambucicola (Homoptera: Aphididae)

The significance of kin discrimination for the evolution of sociality is theoretically important. The behavioural response ofPseudoregma bambucicola soldiers to aphids from other colonies was studied to examine the possibility of context-specific kin discrimination. When non-kin aphids were artificially introduced into experimental colonies, they were never killed or removed by soldiers. Field experiments revealed that the soldiers frequently attacked distantly related species such asAstegopteryx bambucifoliae andCeratoglyphina styracicola, but rarely conspecific aphids or congeneric species such asP. koshunensis andP. alexanderi. Another experiment showed that the soldiers showed altruistic defence even when coexisting with non-kin reproductives. These results agree with and extend the results from previous studies of kin discrimination in social aphids. The absence of kin discrimination suggests that some other factors besides higher genetic relatedness may play a prominent role in the evolutionary maintenance of soldier behaviour in aphids.     

The aphid Ceratovacuna nekoashi (Hemiptera: Aphididae: Hormaphidinae) and its allied species in Korea,Japan and Taiwan

The aphid Ceratovacuna nekoashi and its allied species have been a taxonomically difficult group. They form peculiar “cat's‐paw” galls (called “Nekoashi” in Japanese) on Styrax trees and also use Microstegium grasses as their secondary hosts. Through sampling aphids from both Styrax galls and Microstegium grasses in South Korea, Japan and Taiwan, and sequencing their DNA, we made it clear that four distinct species occur in these regions: C. nekoashi (Sasaki), C. oplismeni (Takahashi), C. orientalis (Takahashi) and C. subtropicana sp. nov. In Korea, C. nekoashi forms galls on both S. japonicus and S. obassia, whereas in Japan the species forms galls on the former but not on the latter; our molecular analyses unequivocally indicated the occurrence of a single species in South Korea and mainland Japan. Aphids of the four species on the secondary host were morphologically discriminated from one another. The identity of the primary‐ and secondary‐host generations was also clarified for each species. All four species were found to produce second‐instar sterile soldiers in their Styrax galls, and first‐instar soldiers were found in colonies of C. subtropicana on the secondary host.     

Social structure and the defensive role of soldiers in a eusocial bamboo aphid,Pseudoregma bambucicola (Homoptera: Aphididae): A test of the defence-optimization hypothesis

A complete understanding of the evolution of sociality in aphids requires a detailed knowledge of the patterns of soldier investment in their ecology. The eusocial bamboo aphidPseudoregma bambucicola has a morphologically specialized first-instar soldier caste. The proportion of soldiers was positively correlated with colony size. Within a colony, soldiers were evenly distributed among subcolonies; within each subcolony, however, their distribution was biased toward peripheries which were exposed to many predators. Field experiments introducing natural enemies such asEupeodes confrater (Diptera: Syrphidae) andSynonycha grandis (Coleoptera: Coccinellidae) revealed that the survival rate of these predators was negatively correlated with the density of soldiers, suggesting that soldiers can more or less defend their colonies by killing or removing a range of natural enemies. Observations suggest that large mature colonies attract more predators than newly established small colonies and that, within a colony, the predators attack each subcolony regardless of its position on bamboo shoots. This implies the presence of a positive correlation between colony size and predation risk. Thus, the investment in soldiers seems to reflect the attacking pattern of predators within a colony. These results agree with the defence-optimization hypothesis in soldier investment ofP. bambucicola colonies.     

Altruistic defenders in a gall-forming aphid of the tribe Hormaphidini (Homoptera,Aphididae, Hormaphidinae) on its primary host

Summary. We found defensive behavior in the aphid Hamamelistes miyabei on its primary host plant, Hamamelis japonica, where it forms a spiny gall. Introduction of moth caterpillars into the galls elicited attacking behavior of aphid nymphs with their stylet. Although older nymphs sometimes attacked, first-instar nymphs were the main defenders. Immature and mature galls contained a large proportion of first-instar nymphs. Open galls still contained first-instar nymphs, but the proportion was remarkably smaller. In immature and mature galls, particularly, the molting rate of first-instar nymphs was significantly lower than that of older instars. These data suggest that the defensive strategy of H. miyabei is such that 1) molting of first-instar nymphs is suppressed, 2) the duration of the first instar is prolonged, 3) the proportion of defender nymphs in the gall is elevated, and 4) consequently the colony in the gall is effectively defended against predators. No morphological differences were found either between attacking and non-attacking first-instar nymphs or between molting and non-molting first-instar nymphs. Some first-instar nymphs in open galls had the next instar cuticle developing inside the body. These data suggest that first-instar nymphs of H. miyabei are monomorphic defenders, and that at least some of them are able to develop and reproduce. In addition to the attacking behavior, first-instar nymphs of H. miyabei performed characteristic behaviors such as gall cleaning and hindleg waving. This is the first time that altruistic defenders are described in the primary host generation of an aphid from the tribe Hormaphidini.     

Alarm pheromone eliciting attack and escape responses in the sugar cane woolly aphid,Ceratovacuna lanigera (Homoptera,Pemphigidae)

All nymphal stages and apterous adults ofCeratovacuna lanigera secreted droplets containing an alarm pheromone from their abdominal cornicles when stimulated with a pin. When fresh droplets on piece of filter paper were put near the aphids, 1st-instar nymphs originating from apterous adults attacked it, but the advanced instar nymphs and adults escaped from the spot. Nymphs and adults originating from alate adults showed escaping behavior only. These different responses strongly correlated with morphological differences, such as relative lengths of the frontal horns and legs. When a syrphid larva,Allograpta javana, was placed on a colony of aphids, many 1st-instar nymphs attacked it using their frontal horns. During the attack, these nymphs spontaneously secreted droplets and adhered them to the syrphid body. When these droplets were placed on the body, the syrphid larva was agressively attacked by additional 1st-instar nymphs.     

Reproductive schedule and factors affecting soldier production in the eusocial bamboo aphid Pseudoregma bambucicola (Homoptera, Aphididae)

Summary: The reproductive characteristics of the soldier-producing aphid Pseudoregma bambucicola were studied in Kagoshima, Southern Japan, to know the factors affecting soldier production of eusocial aphids. The soldier proportion in aphid colonies was highest from October to November. In some large colonies, soldiers were observed in all seasons except in July when colony size was relatively small. Multiple regression analysis showed that the colony size was a principal factor affecting soldier proportion throughout a year. Other social or environmental factors such as aphid composition, host plant conditions and predator abundance were not always significant. Rearing experiments revealed that large colonies (̿,000 individuals) produced soldiers in almost all seasons while small colonies (<1,000) never produced any soldiers. The caste-production schedule of adult females was examined in the field. When solitary females produced both castes, they usually produced normal nymphs first and then soldiers. Females from large colonies tended to produce more soldiers in the earlier period of their lifetime, whereas females from newly established small colonies produced no or only a few soldiers at later times. The average number of soldiers and normal nymphs produced consecutively by a single female was >10 and >20, respectively. Because they have a small number of ovarioles (<15 on average), females should alter caste production within the same ovarioles according to changes in environmental conditions. Artificial removal or introduction of predators and reduction of colony size did not affect soldier production over two successive generations, revealing maternal effects on soldier production. Females cannot shift caste production quickly in response to changes in predator abundance and colony size. This is probably due to early developmental determination of castes within the mother's body.     

Natural occurrence of Gibberella fujikuroi and its potential for control of the woolly aphid Ceratovacuna lanigera (Homoptera: Aphididae) in Indian sugarcane plantations

Studies were conducted to determine the natural occurrence of entomopathogenic fungi and their potential for utilisation in biological control of the woolly aphid (Ceratovacuna lanigera Zehntner) in Indian sugarcane plantations. A fungus Gibberella fujikuroi (Sawada) Wr. (Synonym: Fusarium verticillioides (Sacc.) Nirenberg, Synonym: Fusarium moniliforme (Sheld.) emend. Snyd. and Hans.) was found to be a promising biocontrol agent. It was further characterised and its field performance was studied. Reductions of aphid populations up to 60% were observed when the fungus was applied as two sprays at a week interval in the field.     

Spermatogenesis in the aphid Amphorophora tuberculata (Homoptera,Aphididae)

Spermatogenesis was studied in Amphorophora tuberculata Brown & Blackman, a species of aphid with n=2. Spermatogonia have 2=3 (AA+XO). In early prophase I the autosomal homologues are united terminally to form a tandem bivalent. No evidence could be found of synapsis or of the formation and terminalisation of chiasmata. The terminal connection of the autosomes is retained until late in prophase II. Sister chromatids separate, and autosomal half-bivalents move apart at anaphase I, but the division is incomplete, the X chromosome forming a thin chromatin bridge between the two autosomal half-bivalents. In prophase II the autosomal half-bivalents double back on themselves, so that non-sister chromatids become aligned in parallel. The X chromosome then becomes associated with one of the autosomal half-bivalents. Anaphase II separates the non-sister chromatids, and meiosis is thus post-reductional.     

Spiroplasma symbiont of the pea aphid, Acyrthosiphon pisum (Insecta: Homoptera)

From a laboratory strain of the pea aphid, Acyrthosiphon pisum, we discovered a previously unknown facultative endosymbiotic bacterium. Molecular phylogenetic analysis based on 16S ribosomal DNA revealed that the bacterium is a member of the genus Spiroplasma. The Spiroplasma organism showed stable vertical transmission through successive generations of the host. Injection of hemolymph from infected insects into uninfected insects established a stable infection in the recipients. The Spiroplasma symbiont exhibited negative effects on growth, reproduction, and longevity of the host, particularly in older adults. Of 58 clonal strains of A. pisum established from natural populations in central Japan, 4 strains possessed the Spiroplasma organism.     

Additions to the British aphid fauna (Homoptera: Aphidoidea)

Twenty-five species and two subpecies of aphids are listed and dicussed as additions to the Brutish fauna since publication of "Additions and amendment to the Cheack List British aphids" subspecies is described as new to sicence.     

Demography of soybean aphid (Homoptera: Aphididae) at summer temperatures

Soybean aphid, Aphis glycines Matsumura, is now widely established in soybean, Glycine max L., production areas of the northern United States and southern Canada and is becoming an important economic pest. Temperature effect on soybean aphid fecundity and survivorship is not well understood. We determined the optimal temperature for soybean aphid growth and reproduction on soybean under controlled conditions. We constructed life tables for soybean aphid at 20, 25, 30, and 35 degrees C with a photoperiod of 16:8 (L:D) h. Population growth rates were greatest at 25 degrees C. As temperature increased, net fecundity, gross fecundity, generation time, and life expectancy decreased. The prereproductive period did not differ between 20 and 30 degrees C; however, at 30 degrees C aphids required more degree-days (base 8.6 degrees C) to develop. Nymphs exposed to 35 degrees C did not complete development, and all individuals died within 11 d. Reproductive periods were significantly different at all temperatures, with aphids reproducing longer and producing more progeny at 20 and 25 degrees C than at 30 or 35 degrees C. Using a modification of the nonlinear Logan model, we estimated upper and optimal developmental thresholds to be 34.9 and 27.8 degrees C, respectively. At 25 degrees C, aphid populations doubled in 1.5 d; at 20 and 30 degrees C, populations doubled in 1.9 d.     

Characterization of microsatellite loci in the aphid species Metopeurum fuscoviride (Homoptera,Aphididae)

Small distance movements are of great importance for the dynamics of local populations of insects and can indirectly be assessed using molecular markers. We isolated six polymorphic microsatellite loci in the aphid species Metopeurum fuscoviride Stroyan, monophagous on the common Tansy (Tanacetum vulgare L.). Twenty‐five to 30 aphids from seven populations were analysed. Between three and 17 alleles were found per locus and expected heterozygosities ranged from 0.14 to 0.79. In total, 114 multilocus genotypes were found in 192 parthenogenetic aphids analysed, indicating that the resolution will be high enough to study differentiation on a small spatial scale.     

Studies on the morphometry of the green peach aphid, Myzus persicae (Sulzer) (Homoptera: Aphididae)

Aphids are one of the most important groups of phytophagous insects because of their polyphenism, host alternation, heteroecious behavior and reproductive habits. Laboratory culture of the aphid Myzus persicae on the host plant Brassica pekinensis Hubner was maintained seasonally for biometrical studies. The metric analysis revealed gradual developmental changes from the first instar nymph to the adult stage in size, shape, and a number of characters. The transitional changes were sufficiently distinct to allow differentiation of each of the life stages irrespective of the season. A key to the nymphal stages of the pest is provided.     

An account of the alienicolous morphs of the aphid Patchiella reaumuri (Kaltenbach, 1843) (Homoptera: Aphidoidea)

The alienicolae of Patchiella reaumuri (Kaltenbach), which is heteroecious between Tilia x vulgaris Hayne and roots of Arum species, are here described from material reared on Arum maculatum L. and A. italicum Mill. in 1977. The sexupara morph is also described for the first time from specimens obtained in the same culture. Key couplets are offered whereby this morph can be separated from sexuparae of other British Pemphiginae.     

New species of the aphid tribe Macrosiphini (Homoptera,Aphididae, Aphidinae) from Kazakhstan

Two new species of the genera Uroleucon Mordvilko, 1914 and Pleotrichophorus Börner, 1930 are described from Kazakhstan. Uroleucon dzhungaricum sp. n. feeding on Senecio nemorensis L. (Asteraceae) in the Dzhungar Ala Tau is closely related to U. minor (Börner, 1940). Both these species differ from the closely related U. solidaginis (Fabricius, 1794) in a smaller length ratio between the processus terminalis and the 3rd antennal segment (0.8–1.0 versus 1.0–1.5). The new species differs from U. minor (Born.) in a greater number of the secondary rhinaria on the 3rd antennal segment of the apterous viviparous females (21–37 versus 15–21), in a fewer number of hairs on the cauda (10–16 and 15–23), and in the host plant. Pleotrichophorus ugamicus Kadyrbekov, sp. n. feeding on Artemisia santolinifolia Turcz. is described from the Sairam-Ugam Natural Park (Southern Kazakhstan). The new species is similar to P. glandulosus (Kaltenbach, 1846) and P. achilleae Holman, 1965. Pleotrichophorus ugamicus sp. n. differs from these species in the length ratio of the processus terminalis to the base of the 6th antennal segment (4.1–5.0 versus 5.0–9.0 and 5.1–6.2), in that of the ultimate rostral segment to the 2nd segment of the hind tarsus (0.68–0.76 versus 0.80–0.97 and 0.80–0.90), and in the host plant. This species differs from P. glandulosus in the ratio of the length of dorsal hairs on tergites I–V to the basal diameter of the 3rd antennal segment (1.0–1.2 and 1.4–1.7). In addition, the new species differs from P. achilleae in the length ratio of the 3rd antennal segment to the 6th segment (0.56–0.66 versus 0.70–0.87) and to the processus terminalis (0.67-0.82 versus 1.39–1.80), as well as in the shape of the dorsal hairs. A key to the Palaearctic species of the genus Pleotrichophorus is presented.     

Isolation of microsatellite markers from the drepanosiphid aphid Tuberculatus quercicola (Homoptera,Aphididae)

We isolated five polymorphic microsatellite loci from the drepanosiphid aphid Tuberculatus quercicola (Matsumura) that is associated with the Daimyo oak, Quercus dentata Thunberg, using the magnetic particles method. The isolated loci were polymorphic, with four to 16 alleles in 40 aphids. Expected heterozygosities ranged from 0.4 to 0.82. These loci can be used to quantify seasonal changes in clonal diversity in the metapopulation and the extent of clonal mixing in the colonies.     

Secondary host generation of the gall aphid Cerataphis jamuritsu (Homoptera)

Colonies of a Cerataphis species with well‐developed horns were found on the rattan Calamus quinquesstinervis in southern Taiwan. The morphology of first instar nymphs from the colonies accorded well with the morphology of first instar nymphs laid by alates of Cerataphis jamuritsu from galls on Styrax suberifolia, indicating that the rattan aphids are the secondary host generation of C. jamuritsu. Although the aphid colonies were attended by ants, the sharp horns of the first instar nymphs suggest that they might attack predators.