I investigated the seasonal changes of cold tolerance and polyol content in adults of Harmonia axyridis to elucidate their overwintering strategy. Adults decreased their supercooling point and lower lethal temperature only during the winter. Although the seasonal trends for both values were almost consistent, there seemed to be considerable mortality, without being frozen, at -20°C in mid-winter. The pattern for seasonal change in tolerance at moderately low temperatures differed among the temperatures exposed: the survival time at -5°C peaked in winter, but the time at 5 or 0°C peaked in autumn. Because both autumn and winter adults were completely paralyzed only at -5°C and survived much longer at 0°C than at 5°C, the survival time at -5°C indicates the degree of chilling tolerance, whereas the time at 5 or 0°C seems to show starvation tolerance. This beetle accumulated a relatively large amount of myo-inositol during winter. Myo-inositol content synchronized seasonally with supercooling capacity, the lower lethal temperature and the chilling tolerance, suggesting that myo-inositol may play some role in the control of cold tolerance in this beetle.

Electroantennogram responses of the polyphagous leafminer Liriomyza sativae and its generalist parasitoid Diglyphus isaea to host and non-host plant odours of L. sativae were investigated. The odours of healthy leaves can elicit distinct EAG responses in L. sativae. The EAG responses to the odours of the host plants, bean and tomato, were stronger than to non-host plants, Chinese rose and morning glory. Neither healthy host nor non-host plants of the leafminer elicited distinctive EAG responses in the parasitoid, D. isaea. Odours of physically damaged leaves, no matter whether of host or non-host plants, increased strongly the EAG responses of the leafminer and its parasitoid. We compared the EAG responses of D. isaea to bean leaves of different status. The odour of mined leaves elicited distinct EAG responses, which were weaker than those of physically damaged ones. No differences were detected in the EAG response to leaves with empty mines, healthy leaves or an air control. The role of plant odours in host location of the leafminer and its parasitoid is discussed.

A laboratory study was carried out on photoperiodic control of prepupal diapause in the egg parasitoid Trichogramma embryophagum (Hartig). All experiments were conducted with an isofemale parthenogenetic strain. The maternal generation was reared at 20°C and photoperiods of L:D = 3:21, 6:18, 9:15, 12:12, 15:9, 18:6, 21:3 or 24:0. The tendency to diapause in the progeny was estimated by rearing the daughter generation at 15°C in the dark. Experiments revealed a long-day type response based on maternal influence on the progeny prepupal diapause. However, significant endogenous fluctuations in the pattern of the photoperiodic curve were revealed in successive laboratory generations reared under constant conditions. The left threshold day-length was very variable, while the right threshold kept relative constancy. Experiments with individual females sequentially offered new host eggs demonstrated that the probability of the progeny entering diapause depends significantly on maternal age. At 20°C and 18L : 6D, the percentage of diapause was maximal (ca 15%) in the progeny eclosed from the eggs laid during 1^st - 2^nd days of maternal life. Then the proportion of diapausing progeny decreased to 0-5% at days 9-11 of female life and later slightly increased in 15-17 days old females. Thus, endogenous factors play an important role in maternal influence on progeny diapause, particularly in environments close to threshold temperature and photoperiod.

Two-choice experiments on prey preferences of a generalist predator Pterostichus melanarius, and five species of slug prey, were conducted in the laboratory. Different preferences of P. melanarius for each of the slug species are described. They are interpreted as the outcome of differing slug species-specific defence mechanisms. The influence of hunger level, temperature, day/light period, condition of slugs and beetles, weight of slugs and beetles, and the sex of beetles were controlled experimentally or statistically. The order of slug species preference for predation by P. melanarius was: Deroceras reticulatum (Agriolimacidae), Malacolimax tenellus, Lehmania marginata (Limacidae), Arion distinctus and A. subfuscus (Arionidae). Efficiency of slugs' species-specific defence mechanisms reflected their phylogeny. Defence mechanisms of slugs from the superfamily Arionoidea were significantly more effective at deterring an attack of non-specialised ground beetles than the defence mechanisms of slugs from Limacoidea superfamily. P. melanarius significantly preferred Agriolimacidae to Limacidae, and Limacidae to Arionidae. Slug species was the strongest factor influencing prey preferences of P. melanarius amongst slug prey. Surprisingly, this preference was much more significant than the slug weight. Weight and sex of P. melanarius had no impact on its prey preference.

The magnitude, direction and symmetry of intraguild predation (IGP) between the developmental stages of the aphidophagous Harmonia axyridis Pallas and Coccinella undecimpunctata L. were characterized and compared. Mobility and body weight were the main factors affecting the magnitude of IGP.
H. axyridis was more often the predator than C. undecimpunctata and eggs the most vulnerable developmental stage. There was significant asymmetrical IGP on eggs by the second and later, and fourth larval stages of H. axyridis and C. undecimpunctata, respectively. Asymmetrical IGP of pupae was only recorded for the fourth larval stage of H. axyridis. There was no IGP between adults, but larvae of both species attacked heterospecifics. The best model of the relationship between rate of predation and the difference in the body weight of IG predator and prey differs for the two ladybirds. A small difference in the body weights leads to a marked increase in the rate of predation in H. axyridis but not in C. undecimpunctata. In asymmetrical combinations, increase in body weight of the intraguild predator did not significantly increase the rate of predation. Mobility and body weight were not the only important parameters involved in the symmetry of IGP. Aggressive behaviour of H. axyridis negatively affected the survival of C. undecimpunctata.

Reproduction in Aphelinus albipodus (Hayat & Fatima) from China on Diuraphis noxia (Mordvilko) hosts was studied in the laboratory. Studies were conducted at three constant temperatures, 10.0, 21.1, and 26.7°C (± 1.0°C), 14L : 10D photoperiod, and 50-70% R.H. The longevity of both males and females was greatest at 10.0°C (26.0 and 41.5 d, respectively); differences in longevity were not significant (p > 0.05) between 21.1 and 26.7°C in both sexes (males 13.1 vs. 10.0 d, females 20.9 vs. 16.4 d, respectively). Fecundity was greater at 26.7 (294.7 ± 27.6 mummies) and 21.1°C (214.8 ± 33.5 mummies) than at 10.0°C (569 ± 11.7 mummies), but was not significantly different (p > 0.05) between the former two temperatures. Aphelinus albipodus did not successfully develop to adulthood at 10°C, thus r_m and R_o values were zero, and T_c (generation time) could not be estimated. At 21.1°C, r_m = 0.188, R_o = 68.9, and T_c = 23.9 d; those values were 0.288, 67.4, and 15.2 d, respectively, at 26.7°C. The offspring sex ratio (females) was male-biased at all three temperatures: 0.364 ± 0.061 at 10.0°C, 0.437 ± 0.029 at 21.1°C, and 0.341 ± 0.002 at 26.7°C. Moreover, daily offspring sex ratio decreased with the age of the female parent at all three temperatures (p < 0.05). A pre-oviposition period of 1.5 d was observed in A. albipodus at 10° C, and female offspring were not produced during the first 7.5 d of adult life of mated females. The limited number of ovarian eggs, 6.5 ± 2.5, in newly emerged females (< 6 h old) together with their fecundity schedule indicated synovigeny in A. albipodus. Results are discussed in relation to the colonization in North America of A. albipodus for biological control of D. noxia.

The endemic Costa Rican genus Zurquilla Gauld, 1997, is transferred from the ichneumonid subfamily Tryphoninae (tribe Oedemopsini) to the Cryptinae (tribe Phygadeuontini) and synonymised with Nipponaetes Uchida, 1933. This decision is justified using morphological and molecular (28S D2-3 ribosomal DNA sequence) evidence. We briefly discuss the phylogenetic utility of characters that led to the type species of Zurquilla being described as a tryphonine and provide a host record that indicates that Nipponaetes is a parasitoid of spider egg sacs.

A 1962 bp cDNA clone of 5-aminoimidazole-4-carboxamide ribonucleotide formyltransferase/IMP cyclohydrolase (purH) was isolated from diapausing adults of Leptinotarsa decemlineata using RT-PCR and 3' and 5'-RACE. The probe generated from this clone hybridized to a transcript approximately 1960 bp in length on northern blots. The clone encodes for a deduced protein 594 amino acids in length with 73% identity, 83% similarity to purH from Drosophila melanogaster. Northern blot (total RNA) analysis determined that L. decemlineata purH (LdpurH) was downregulated in diapausing beetles stored at 10°C. Developmental studies revealed that LdpurH is expressed at nearly constant high levels in both nondiapausing and prediapause adults. LdpurH expression during the first 20 days of diapause is equivalent to that seen in nondiapausing beetles, after which expression decreases. Exposing 70 day old diapausing beetles to 20°C for 24 h induced an increase in expression of purH indicating that purH is regulated by temperature in diapausing/overwintering beetles.

A general model of the Dolichopoda cave cricket life cycle was produced using RAMAS/stage simulations based on the Beverton & Holt recruitment function. The model indicates the main population parameters responsible for life cycle adjustments to ecologically different cave habitats. The lack of a uniform rate of oviposition throughout adult life, combined with egg and nymphal diapause, results in regular population growth characterized by adults emerging every two years and cohorts overlapping every other year. This pattern is common in populations living in artificial caves where the scarcity of food is likely to favour individuals that synchronise their activity with the seasonal variations in the epigean habitat. In contrast, a uniform rate of oviposition throughout adult life and no egg or nymphal diapause results in a continuous reproductive activity, and the occurrence of adults all the year round. In this case, it was not possible to distinguish between cohorts. This pattern is well represented in populations inhabiting natural caves with stable food resources. The availability of data for a population that resulted from an experimental colonization allowed us to test this model.

Kluwer Academic Publishers, Dordrecht, The Netherlands, 2002, 330 pp.

The endoparasitoid Glyptapanteles liparidis (Hymenoptera: Braconidae) injects polydnavirus and venom together with eggs into its Lymantria dispar (Lepidoptera: Lymantriidae) host larvae during oviposition. We studied effects of these parasitoid associated factors by means of g-irradiation-induced pseudoparasitization. The application of radiation for sterilization of female wasps as a tool to study interactions between parasitoid associated factors and the host is demonstrated in this paper. When wasps were irradiated at doses ranging from 24 to 96 Gy and then allowed to oviposit into L. dispar larvae, temporary sterilization was produced. On the first day post irradiation they laid 99% sterile eggs, but fertility recovered partially during the following days. Irradiation had no negative effect on the lifespan of wasps, but total fecundity was significantly reduced. Pseudoparasitization of L. dispar by irradiated G. liparidis caused prolonged larval development with supernumerary molts before pupation in females, and higher pupal weights in both sexes. Only 8 to 20% of pseudoparasitized larvae developed into adults; 20 to 33% died as larvae, 55 to 65% in pupae. Abnormities, such as precocious formation of pupal antennal pads in larvae or incomplete sclerotization of pupal cuticle occurred. Pseudoparasitization impaired the immune reactions of L. dispar larvae. Encapsulation of implanted plastic rods by hemocytes was reduced and hemolymph melanization was significantly suppressed 3 and 5 days post pseudoparasitization.

Ten ant species (Hymenoptera: Formicidae) from three subfamilies feed on honeydew excreted by nymphs of the leafhopper Balclutha punctata (Hemiptera: Cicadellidae). This relationship is facultative for the partners. Preliminary field observations suggest a mutualistic interaction that represents an intermediate stage in the spectrum of formicid-hemipteran mutualisms. Behavioural adaptations of the leafhopper (no escape reaction) and the ants (no predation of leafhoppers, protection from spiders) are evident, but characters of advanced facultative mutualism such as physical contact between the partners or ant-triggered excretion of honeydew were not observed.

We analysed the chromosome complement and male meiosis in a natural population of Mepraia gajardoi (Hemiptera: Reduviidae: Triatominae). The normal karyotype of this species is 20 autosomes plus X₁X₂Y in males and X₁X₁X₂X₂ in females. We confirmed that M. gajardoi is cytogenetically strikingly different from M. spinolai (with which it was previously included), which supports the taxonomic separation of these two species. For the first time in the holocentric chromosomes of the subfamily Triatominae, a structural rearrangement was detected. Observations made during meiosis and mitosis indicated that one of eleven individuals had undergone a fusion between two non-homologous chromosomes, probably before germinal cell development. This autosomal translocation resulted in chromosomal irregularities such as an autosomal trivalent, autosomal univalents and chromosomal fragments, which altered the normal segregation of both autosomes and sex chromosomes. The chromosomal fragments resemble supernumerary or B chromosomes, which supports the idea that these chromosomes are remnants of structural rearrangements. The genetic consequences of translocations in holokinetic chromosomes and their role in the evolution of chromosomes in triatomines are also discussed.

The comparative biology of the solitary endoparasitoid Meteorus gyrator (Thun.) was investigated in five noctuid pest species. Meteorus gyrator parasitized all larval stages of the noctuid pests Lacanobia oleracea, Mamestra brassicae, Spodoptera exigua, Spodoptera littoralis and Chrysodeixis chalcites. When female parasitoids were offered host larvae of all developmental stages, host larvae in their third stadium were parasitized most frequently in all species. When the parasitoid was offered a choice of third stadium larvae from each of the five lepidopteran host species, L. oleracea was the most frequently parasitized, followed by M. brassicae. The growth of L. oleracea and M. brassicae was markedly reduced when larvae were parasitized by M. gyrator, with the effect of parasitism on the remaining species being much less pronounced. In excess of 94% of parasitized hosts gave rise to live wasps in L. oleracea, whilst in M. brassicae only 52% of parasitized hosts gave rise to a live wasp, the remainder dying (44.6%) or pupating (3.1%).
The larval development of the parasitoid was also strongly influenced by the host species. Thus, the development (egg to cocoon) of female wasps was most rapid in C. chalcites (9.7 ± 0.09 days), and longest in M. brassicae (17.2 ± 1.08 days). The cocoon weight of wasps was also significantly affected by host species, with the heaviest female cocoons being derived from C. chalcites (10.4 ± 0.16 mg) and the lightest female cocoons being derived from M. brassicae (7.0 ± 0.14 mg). In all cases, the development times and cocoon weights of male parasitoids were less than those of female wasps.

Adult diapause in Riptortus clavatus (Thunberg) was induced by short-day photoperiods, and the critical daylength for its induction was 13.5 h. When insects were reared from eggs under diapause-inducing photoperiods near the critical daylength, the duration of diapause was shorter than when reared under the shorter daylengths. Adults terminated diapause under long-day photoperiods earlier when they had been raised under a near-critical photoperiod than under shorter daylengths; this indicated that the initial intensity of diapause was dependent on the length of the inducing photoperiod. Not only the photoperiods experienced during preimaginal development but also the value of the long-day photoperiods experienced after adult emergence affected the time of onset of oviposition. When the photophase was shortened, either abruptly or gradually after adult emergence, the duration of diapause was prolonged. Diapause was long when induced by shorter daylengths than the near-critical photoperiod. Different photoperiods have thus different quantitative effects on both the initial intensity of diapause and the rate of diapause development.

Some behavioural aspects of the reproductive biology of Megaselia andrenae Disney, a kleptoparasite of the communal bee Andrena agilissima (Scopoli), were investigated at the nesting site of its host at Isola d'Elba (Italy). The scuttle fly mates more often in the early afternoon, which coincides with the period when the provisioning flights of its host are more frequent. The presence of the flies at the host nesting site, either in copula or single, is lower in the morning. In general only the females enter the host nests immediately after a mate, in a few cases closely followed by the males. When leaving the nest, females refuse to mate again with the males waiting outside. Observations on the ovaries of the females revealed no differences, either in the number of eggs or in the length of the most mature egg, between the individuals collected in copula or when flying alone. The species is sexually dimorphic, the females being larger than males. Male size does not seem to influence the females choice for mating.

Proceedings of the 6^th International Symposium on Aphids, September 2001, Rennes, France. INRA Editions, Versailles-Paris, 2004, 549 pp. ISBN 2-7380-113-6. Price EUR 62.00.

Attraction of first instar larvae of Spodoptera litura to different colours was studied to determine those that could be used as effective visual attractants for trapping the larvae during dispersal. The larvae were presented with cones of coloured paper. Each cone was placed in the center of a 15-cm Petri dish around the edge of which the larvae were released. Percentage of larvae arriving at the cone was recorded at 5-min intervals over a 15-min period. Differences in the percentages reflected differences in larval attraction to the different colours. The larvae were highly attracted to Foliage Green, Green Bice and Cadmium Yellow. The larvae arrived at the Scarlet Red, Ultramarine Blue, Gray, Orange, White and Black cones in percentages that were almost equal, but lower than at the Foliage Green, Green Bice and Cadmium Yellow cones. Arrival of larvae at the coloured cones increased with time, but their relative preference for different colours remained the same. This study shows that green and yellow can be used as visual attractants in Spodoptera litura larval traps.

Rhythms in abdominal pumping, heartbeats and discontinuous gas exchange cycles (DGCs) of CFV subtype (closed, flutter and ventilation periods) in adults of pine weevil Hylobius abietis were simultaneously recorded using an electrolytic microrespirometer and an infrared (IR) cardiograph or IR actograph (IRA). The cyclic release of carbon dioxide was associated with active ventilation (V phase) provided by vigorous abdominal pumping movements due to contractions of tonic longitudinal and transversal abdominal muscles, which are visible to the naked eye. On the IRA-recordings, the abdominal pumping signals are superimposed on the heartbeat spikes. The relative amplitude of the abdominal pumping signals on these recordings is more than 10 times greater than that of the heart beats. Visual observations showed that the subelytral cavity appeared to be closed during the release of carbon dioxide and open at other times. The flutter (F) of the CFV cycle is characterised by active miniature inspirations or ventilations before the V period. The miniature ventilation movements were imperceptible to the naked eye, but were recorded on the respirometer-actigraph as clear spikes. In addition, movements of the tip of the abdomen, of between 10-20 mm were seen under a stereomicroscope at a magnification of 40×. Some cycles were categorized as (C)FV cycles, when the C period disappears into the end of the V period. Abdominal pumping and miniature inspirations were clearly synchronized with the CFV cycles. Abdominal pumping movements, miniature inspirations or ventilations and heartbeats in adult H. abietis were distinguishable when recordings of the electrolytic microrespirometer-actograph and IRA were made in parallel. These three events were recognized by their different amplitudes and frequencies. It is presumed that abdominal pumping and miniature inspirations in adult H. abietis are obligatory rhythmic movements of different function and origin.

Intercept, Andover (UK), 2004, xx + 301 pp.

The relations between the patterns of discontinuous gas exchange cycles (DGCs) and water loss were investigated in non-chilled diapausing pupae of the white cabbage butterfly Pieris brassicae kept at room temperature (22-24°C) in Petri dishes. An electrolytic respirometer, combined with an infrared (IR) actographic device was used for the simultaneous recordings of metabolic rate, cyclic release of carbon dioxide (bursts), passive suction inspirations (PSIs) and body movements. The patterns of cyclic gas exchange in four- and five-month-old non-chilled diapausing pupae varied individually to a considerable extent. About 40% of the pupae displayed long DGCs lasting 1-3 h, while the interburst periods were characterised by rare and almost regular large PSIs succeeding at intervals of 1-4 min. Nearly 30% of the pupae exhibited short DGCs lasting 3-5 min, while between the bursts there occurred unclear frequent gas exchange microcycles. Standard metabolic rate (SMR) did not reveal significant differences between long DGCs and short DGCs ranging from 32-56 (mean 47.6 ± 4.6) ml O₂ g^-1 h^-1, and 28-61 (mean 44.95 ± 5.3) ml O₂ g^-1 h^-1, respectively. The mentioned levels of SMR were characteristic of diapausing pupae.
Water loss in pupae with long DGCs was determined gravimetrically to be 0.29 ± 0.1 mg g^-1 day¹. At the same time, water loss in pupae that showed only short DGCs and irregular microcycles was 1.73 ± 0.31 mg g^-1 day^-1, which was significantly higher than in individuals characterised by long DGCs. We suggest that water loss in the non-chilled diapausing pupae may depend significantly on the patterns of cyclic gas exchange: long cycles and rare but deep PSIs exerted a marked water conserving effect.

We describe here the in vitro rearing of Anagrus breviphragma Soyka, an egg parasitoid of Cicadella viridis (Linnaeus), from the second instar larva to the adult stage. Three media, containing mainly either a commercial tissue culture medium (IPL-41), skimmed milk or veal homogenate, were tested. Larval development occurred on all the diets but few larvae reached the pupal stage on the diets containing skimmed milk or veal homogenate. On the tissue culture medium, pharate adults, albeit malformed, developed. Supplementing the tissue culture medium-based diet with chicken egg yolk alone, or combined with yeast extract, further improved parasitoid development. The addition of both egg yolk and yeast extract resulted in twelve out of twenty larvae reaching the adult stage, of which only four females emerged.

The wounds inflicted on pupae in capped brood cells of the honey bee, Apis mellifera, infested with a single female of the ectoparasitic mite, Varroa destructor, were investigated after visualisation by vital staining with trypan blue. On average the mites made two integumental perforations for feeding on prepupae and one on pupae. Most of the punctures were on particular ventral sites on the abdomen. Possible reasons for this pronounced preference and the evolutionary aspects of this highly specialised parasite-host relationship are discussed.

The inhibitory potential of primary and secondary reproductives was studied using half-orphaned colonies of Kalotermes flavicollis. Both primary and secondary reproductives (neotenics) were equally effective in inhibiting the development of replacement reproductives. Single females totally inhibited the development of female secondary reproductives but did not affect the development of male secondary reproductives. Single males had neither a stimulatory nor inhibitory effect on the development of secondary reproductives. The inhibitory ability of pairs of primary reproductives shortly after dealation and at the stage of incipient colony formation (couple with the first batch of eggs) was also examined. While pairs of freshly dealated reproductives were not able to inhibit the development of neotenics, pairs of primary reproductives that had their first batch of eggs, fully inhibited the development of neotenics.

The effect of wing length (brachyptery and macroptery) on mating activity was investigated in adult males and females of a flightless wing-polymorphic insect, Pyrrhocoris apterus (L.). Mating activity of the brachypterous and macropterous adult bugs was assessed according to 14 different parameters. The competition tests revealed higher numbers of copulations and greater duration of mating activity in brachypterous than in macropterous males. Brachypterous males are between two to four times more successful in competition for females than their macropterous counterparts, depending on the wing morph and physiological status of the females. Decreased mating success of macropterous males is associated with the smaller size of their accessory glands. Lowered competitive ability for mates is a likely penalty associated with macroptery. Receptivity tests showed the highest tendency to mate in reproductive brachypterous females, lower in macropterous females and the least in diapausing brachypterous females. This is the first report of decreased mating propensity of macropterous morphs in insects with non-functional wing polymorphism. The association of lowered mating success with the higher dispersal activity of the macropterous morph in this bug and a trade-off between the ability to reproduce and to disperse in the flightless wing-polymorphic insects is discussed.

The aim of this study was to show that the kind of AKH-mobilized energy substrates in insects can be predicted on the basis of the results obtained with the application of heterologous, i.e. inter-species, AKHs. Four different AKHs, the Locmi-AKH-I inducing hyperlipaemia and hyperglycaemia in Locusta migratoria, Tenmo-HrTH inducing hyperglycaemia in Tenebrio molitor, and Pyrap-AKH and Peram-CAH-II inducing hyperlipaemia in Pyrrhocoris apterus were used, firstly in conspecific tests, secondly in all possible species-AKH combinations, and finally in individual applications on the test species, the cotton bug Dysdercus cingulatus. Since each of the AKHs induced hyperlipaemia in D. cingulatus adults, we predicted that lipids are the only energy substrates which are mobilized in this species by its native AKH. The accuracy of this prediction was subsequently confirmed by the structural identification of the native D. cingulatus AKH and conspecific application tests. The proposed methodical approach can serve as a suitable monitoring system for determination of the kind of energy substrates mobilized by native insect AKHs until the structure of the hormone is identified.

The cocoons characteristic of the prepupal and pupal stages of many insects vary widely in size, durability, structure, shape and colour, as well as in other features such as orientation and attachment to the substrate. In some species they vary seasonally. Most cocoons provide little direct insulation, although they may reduce the rate at which temperature changes, but many provide the mechanical protection required for overwintering beneath insulating substrates such as soil and snow. The cocoons of some terrestrial species prevent inoculative freezing by isolating the integument from ice crystals on the cocoon surface or its surroundings. In some aquatic species, cocoons appear to limit damage by providing mechanical protection during the freezing of surrounding water. Some cocoons help in the acquisition of solar heat: dark structures are especially effective because dark pigments absorb heat, and surrounding layers trap this heat. Insects are immobilized when it is cold and so cannot move in response to environmental threats, and protective cocoons made for winter tend to be more robust than their summer counterparts. Such cocoons protect against abrasion of the waterproof layer of the cuticle. In some species, robust cocoons or complex structures impede natural enemies. Cocoon silk has anti-bacterial and anti-fungal actions. Other cocoons are more or less waterproof. These and other features withstand simultaneous constraints in addition to cold. Therefore, cocoons enhance survival during cold conditions in many species. However, this conclusion is based on fragmentary evidence, and there has been relatively little explicit examination of the roles of cocoons during winter. Therefore, specific work is required to assess resistance to or enhancement of inoculative freezing, resistance to penetration by natural enemies and water, the roles of particular cocoon silks and silk constituents, and the quantitative contributions of cocoons to winter survival in nature.

Cold tolerance of the eggs of the grasshopper, Chorthippus fallax (Zubovsky), was examined in the laboratory. Egg supercooling points varied from -6°C to -32.4°C and could be divided into two groups. The supercooling points of the higher SCP group ranged from -6°C to -14°C and those of lower SCP group from -21.8°C to -32.4°C. Although low temperature acclimation could slightly decrease the supercooling points of eggs, the effect was not significant for all embryonic developmental stages or acclimation periods. The supercooling capacity was obviously different between pre-diapause, diapause and post-diapause embryonic stages. The mean supercooling points of pre-diapause and diapause eggs were similar; -28.8 ± 1.6°C and -30.7 ± 1.0°C for non-acclimated eggs and -29.5 ± 1.3°C and -31.18 ± 0.8°C for acclimated eggs respectively. However, the mean supercooling points of post-diapause eggs were significantly higher; -12.9 ± 5.6°C for non-acclimated and -13.5 ± 4.5°C for acclimated eggs respectively. The survival rates of diapause eggs at > -25°C were not significantly different from that at 25°C, but survival rates at < -30°C decreased significantly. The lethal temperature (Ltemp₅₀) for a 12 hrs exposure was -30.1°C, and the lethal time (Ltime₅₀) at -25°C was 44 days. Since the SCPs of diapause eggs was similar to their Ltemp₅₀, we may consider the supercooling capacity of such eggs is a good indicator of their cold hardiness and the species is a true freeze avoiding insect. Based on the analysis of local winter temperature data, pre-diapause and diapause, low SCP eggs can safely survive severe winters, but not the post-diapause, high SCP eggs. The importance of the overwintering strategy and the relationship between diapause and cold hardiness of this species is discussed.

The aphids Schizaphis graminum (Rondani) (greenbug) and Diuraphis noxia (Mordvilko) (Russian wheat aphid, RWA) were collected from several localities in Argentina and Southern Chile. Clones were established from aphids collected at each location. The host preferences were studied in free choice tests. Biotypes were characterized on the basis of aphid antibiosis and host plant tolerance. The production of sexuals was assessed under natural conditions, from March to November in 1997-2001, at La Plata (34°55' S, 57°57' W). The greenbug distribution ranged from 24°40' to 43°28' S, and was bounded between isothermals 18-20°C and 8-10°C, and isohyets 400-600 mm and greater than 1200 mm. The aphids at all localities were collected from a wide range of cultivated and wild hosts. The biotypes in ten out of thirty-four populations were identified. One population was obligatorily parthenogenetic, the remainder cyclically parthenogenetic. No correlation was found between the region they came from and the period required for the induction of sexuals. RWA was found between 26°50' and 43°28' S, bounded by the isothermals 20-22°C and 8-10°C, and isohyets 400-600 mm and 2000 mm. In Chile, this aphid was only found in Osorno County, which lies on isothermal 8-10°C and is bounded by the isohyets 1000 mm and 2000 mm. Only a few RWA genotypes (clones) produced sexuals irrespective of the host they were collected from, period of the year, region, current host, or the day length and average temperature of the rearing conditions. For the first time, RWA was found infesting cultivated as well as wild oats in South America. At low latitudes, populations of both aphid species were found only infesting wild Sorghum halepensis (L).

We recorded the association between the planthopper Tettigometra laetus Herrich-Schäffer, 1835 (Hemiptera: Fulgoromorpha: Tettigometridae) and three ant species belonging to the subfamilies Myrmicinae and Formicinae in a coastal dune area of Flanders (Belgium). Lasius psammophilus Seifert, Tetramorium caespitum L. and Formica cunicularia Latreille were observed attending and palpating the dorsal glandular area of this planthopper, taking honeydew directly from its anus, herding them and carrying them into their nests when disturbed. The planthopper was rarely found in the absence of ants and probably develops within ant nests, which may provide protection against predation and adverse weather conditions. The natural history of temperate ant-hemipteran relationships is discussed.