Aphis Fabae Scopoli Research Articles

Does urbanization explain differences in interactions between an insect herbivore and its natural enemies and mutualists?

Urbanization can alter the composition of arthropod communities. However, little is known about how urbanization affects ecological interactions. Using experimental colonies of the black bean aphid Aphis fabae Scopoli reared on Vicia faba L, we asked if patterns of predator-prey, host-parasitoid and ant-aphid mutualisms varied along an urbanization gradient across a large town in southern England. We recorded the presence of naturally occurring predators, parasitoid wasps and mutualistic ants together with aphid abundance. We examined how biotic (green areas and plant richness) and abiotic features (impervious surfaces and distance to town center) affected (1) aphid colony size, (2) the likelihood of finding predators, mutualistic ants and aphid mummies (indicating the presence of parasitoids), and (3) how the interplay among these factors affected patterns of parasitoid attack, predator abundance, mutualistic interactions and aphid abundance. Aphid abundance was best explained by the number of mutualistic ants attending the colonies. Aphid predators responded negatively to both the proportion of impervious surfaces and to the number of mutualistic ants farming the colonies, and positively to aphid population size, whereas parasitized aphids were found in colonies with higher numbers of aphids and ants. The number of mutualistic ants attending was positively associated with aphid colony size and negatively with the number of aphid predators. Our findings suggest that for insect-natural enemy interactions, urbanization may affect some groups, while not influencing others, and that local effects (mutualists, host plant presence) will also be key determinants of how urban ecological communities are formed.

Maternal rearing condition and age affect progeny fitness in the parasitoid waspLysiphlebus fabarum

AbstractMaternal rearing conditions are expected to affect fitness components of progeny so that maternal effects effectively protect offspring from environmental stressors. The objective of this study was to elucidate the interaction between maternal rearing condition, age, and offspring rearing condition in the parasitoid waspLysiphlebus fabarum(Marshall) (Hymenoptera:Braconidae,Aphidiinae). The effects of maternal age, body size, and host instar used for development on fitness components of progeny were evaluated. Host was the black bean aphid,Aphis fabaeScopoli (Hemiptera: Aphididae). Results indicated that small and young mothers (developing in first‐instar hosts) produced progeny with a longer developmental time compared to large and old mothers (developing in second‐instar hosts). Progeny that hatched from larger eggs also had a larger body size. There were, however, no significant differences in the size of progeny that developed in different host instars. Progeny that hatched from large eggs had a higher initial egg load, and progeny produced by younger mothers had larger eggs. These differences were significant only when progeny developed in the first host instar, whereas in the second and fourth instar no differences were observed. Our findings indicate that progeny with larger size at the egg stage had superior fitness. Age‐specific maternal effects were not as strong as the effect of the mother's body size. Although the interaction between host instar of progeny development and maternal rearing condition was not statistically significant, developing in suboptimal instars led to trade‐offs between fitness components in progeny. The ecological significance of these findings is discussed.

Aphids and ladybird beetle’s abundance and diversity in alfalfa fields of Yasouj, southwestern of Iran

Alfalfa (Medicago sativa L.) is the oldest and the most important forage legume. It has been cultivated for forage longer than any other crop. Diversity indices provide information about community composition. Diversity indices are measured by species richness and species evenness therefore, it could give us more ecological information rather than a simple species list in the fields. During 2015-2016, aphids and ladybird beetle’s abundance and diversity were monitored in alfalfa fields of Yasouj. Samplings were conducted with 150 plants in the alfalfa fields from mid-May to mid-November. Species richness was measured using Shannon and Simpson indices. In this study, six aphids and five coccinellid species were collected and identified. Among the collected aphid species, Aphis fabae (Scopoli, 1763) and Therioaphis maculata (Buckton, 1899) were most abundant in the fields. For coccinellids, Coccinella septempunctata L. was the most abundant species. Highest aphid species diversity was observed on 17 May 2016.

English

This study was based on the determination of aphid species that infested Chrysanthemum sp. (Asterales, Asteraceae) in the middle of Iraq; five aphid species belong to subfamily Aphidinae were recorded: Aphis fabae Scopoli, 1763, Aphis gossypii Glover, 1877, Coloradoa rufomaculata (Wilson, 1908), Macrosiphoniella sanborni (Gillette, 1908) and Myzus persicae (Sulzer, 1776). A. gossypii was the most dominant species throughout the study period while M. persicae is the lesser species. A summary of the main taxonomic characters is presented here and a pictorial key which was designed to separate aphid species colonizing Chrysanthemum sp. is also presented.

Cornicle secretions by Aphis fabae (Hemiptera: Aphididae) result in age-dependent costs and improved host suitability for Lysiphlebus fabarum (Marshall) (Hymenoptera: Braconidae).

We examined the life history consequences of cornicle secretion by Aphis fabae Scopoli in second and fourth instars, and its effects on host suitability for its parasitoid, Lysiphlebus fabarum (Marshall). Cornicle secretion did not affect aphid fecundity, but secretion in the second instar enhanced life table parameters, whereas secretion in the fourth instar affected them negatively, suggesting a higher cost of secretion in later instars. Secretion in either instar improved host suitability for L. fabarum. Although control and treated aphids were parasitized at similar rates, and with similar success, wasps developed faster and emerged as larger adults in aphids that had secreted, regardless of instar. Transgenerational effects were also evident. Progeny emergence was higher when parental wasps developed in fourth instars than in seconds, whether aphids secreted or not, and progeny were larger when parental hosts secreted in the second instar, but not in the fourth. Secreting fourth instars were preferred to controls by L. fabarum females in choice tests, but not secreting second instars, and fourth-instar secretion improved wasp emergence. When control aphids were attacked, second instars were more likely to secrete than fourth instars, whereas the latter were more likely to kick the parasitoid. Cornicle secretion reduced the probability of subsequent secretion events and the frequency of other aphid defensive behaviors, indicating energetic tradeoffs among defensive tactics. Overall, our results revealed that cornicle secretion by immature A. fabae exacts both physiological and behavioral costs and results in improved host suitability for its parasitoid.

Are the reproductive traits of two populations of P. quatuordecimpunctata affected by the geographic conditions and the prey species

Life history parameters of the ladybird populations, Propylea quatuordecimpunctata (L.) (Coleoptera: Coccinellidae), collected at two locations in Iran (Karaj and Sari) were recorded on two prey species, Aphis fabae Scopoli, 1763 and Aphis gossypii Glover, 1877 (Homoptera: Aphididae). The duration of most developmental stages (egg, first, second and third instar larvae) of two local populations of P. quatuordecimpunctata differed significantly, except for the fourth instar and pupal periods. A comparison of life table parameters between the two populations with different preys, showed that the net reproductive rate (R0) was not significantly different (P > 0.05). The intrinsic rate of increase (r), the mean generation time (T) and the finite rate of increase (λ) of the population from Sari on A. gossypii, differed significantly from the same population fed on A. fabae (P < 0.05). Our results demonstrated that reproductive traits of two populations of P. quatuordecimpunctata were affected by the geographic conditions and the prey species.

First record and occurrence of Μacrosiphum euphorbiae (Thomas) (Homoptera: Aphididae) on cotton in Central Greece

The potato aphid, Macrosiphum euphorbiae (Thomas), is a highly polyphagous species on secondary hosts feeding on over 200 plant species, but is especially found on Solanum tuberosum L. M.euphorhiae was first noticed on cotton (cv Zeta 2) at Thiva in central Greece in May 1988 during a study on the population dynamics of cotton aphids carried out in a cotton field in the above mentioned region. This species has been recorded on other host-plants in Greece. It resembles Acyrthosiphon gossvpii Mordvilko, a species which also colonizes cotton but has not been recorded yet in Greece. They can be distinguished from each other since the former has shorter siphunculi, hearing a zone of polygonal reticulation on their apices, than the latter. Moreover, it is easily distinguishable from Aphis gossypii Glover, Aphis fabae Scopoli and Aphis craccivora Koch, species which also colonize cotton. A. gossypii is the most important aphid species attacking cotton at Thiva region and has also been recorded previously on cotton by various authors. The species A. fabae and A. craccivora have also been recorded on cotton in Greece. M. euphorbiae was found in the first three samplings that occurred between mid and the end of May when plants were young. From early June and during the rest of the growing season this species was not found in the field. In a total of about 50 plants sampled in each sampling only a few individuals were found. The majority of aphids were alatae, representing 69, 60 and 43 percent of the population at the first. second and third sampling dates, respectively. Alatae started to reproduce on the plants after their alightment, since first and second instar nymphs were present even from the first sampli­ng which took place after the appearance of plants. However, the number of nymphs was kept low during the period M. euphorbiae was present, suggesting that this was possiblydue either to the partial unsuitability of the cotton variety as host or to the effect of the systemic insecticide, phorate which had been applied at sowing, but this needs further investigation. This species was found again in low numbers in another cotton field at Thiva region, from mid May to early June of 1989. The fact that this species was not found from early June onwards in both years reveals that cotton is only a temporary secondary host-plant, possibly not very suitable for aphid development and reproduction. However, cotton may play some role on the population dynamics of M. euphorbiae on subsequent crops and mainly on potatoes, a crop which is widely planted at Thiva region. This might be of particular con­cern because M. euphorbiae is a vector of several viruses.

The forewing of the Aphis fabae (Scopoli 1763) (Hemiptera, Sternorrhyncha): a morphological and histological study

Dorsal and ventral sides of the forewing of Aphis fabae (Scopoli 1763) (Sternorrhyncha, Hemiptera) were examined by scanning electron microscopy. Reinforcement elements on their surface as well as scale-like elements were described. Using histological methods, cross-sections of the material were done. They showed a two-layered membrane with a circular foramen inside. The course of veins and places of their bifurcation were followed. Common stem of radius (R), media (M), and cubitus anterior (CuA) veins were composed of separate tracheae, which ran separately at the beginning, then continued in a single tunnel, and finally disappeared. Nerves were not observed. Neither were tracheae visible on the further course of those veins. The presence of a devoid-of-trachea costal vein was confirmed. Under scanning electron microscope, convex reinforcements on dorsal side of the wing turned out to be more sclerotized parts of chitin, not giving a zigzag-like profile of the wing on sections. In this paper, we show for the first time a cross-section of a very delicate wing of an aphid representative.

Faithful vertical transmission but ineffective horizontal transmission of bacterial endosymbionts during sexual reproduction of the black bean aphid, Aphis fabae

1. Insects are commonly infected with bacterial endosymbionts. In addition to the costs and benefits associated with harbouring these symbionts, their rates of vertical and horizontal transmission are important determinants of symbiont prevalence.2. Aphids are cyclical parthenogens and show virtually perfect maternal transmission of endosymbionts during asexual reproduction. Less clear is the role of the annual sexual generation, during which overwintering eggs are produced. Data from pea aphids (Acyrthosiphon pisum Harris) suggest that maternal transmission failures and horizontal transmission via males may occur under sexual reproduction at least occasionally. No such data exist for other aphid species.3. In the present study, the rates of maternal and paternal transmission of facultative endosymbionts during sexual reproduction in the black bean aphid, Aphis fabae (Scopoli) were examined. Crosses were performed between clones infected with Hamiltonella defensa, clones infected with Regiella insecticola and clones without facultative endosymbionts, and eggs were overwintered under three different conditions.4. Only one of 205 offspring from crosses testing for maternal transmission failed to inherit the symbiont present in the maternal clone, and in crosses testing for horizontal transmission, only one of 412 offspring acquired a facultative symbiont from the father.5. These results show that in A. fabae, maternal transmission of H. defensa and R. insecticola is extremely reliable also during sexual reproduction, indicating that maternal transmission failures are unlikely to exert a significant influence on frequencies of infection in the field. Paternal transmission of endosymbionts was exceedingly rare, suggesting that this route of horizontal transmission may be less important than hitherto assumed.

Flight dynamics and species composition of aphids landing on plum and apricot leaves in the orchards in Western Serbia

More than 40 different aphid species (Hemiptera: Aphididae) landing on plum and apricot trees were captured with Sticky shoot method and identified in the experimental orchards in Western Serbia during 2009–2011. The most abundant species found in 2009 and 2011 belongs to the genus Aphis. In 2010, Myzocallis spp. were most abundant. Specimens of the genus Muscaphis were found for the first time in Serbia. The aphid population dynamics varied greatly during the growing season. Spring peaks of aphid populations were evidenced in all 3 years in the period of May–June. Autumn peaks were recorded during the period of August–September in 2009 and 2011, but not in 2010. Twelve out of more than twenty species reported in the literature as a potential Plum pox virus (PPV) vectors were found in the orchards. Rhopalosiphum padi (Linnaeus), Aphis fabae Scopoli, Aphis craccivora Koch and invasive aphid species Aphis spiraecola Patch were the most common potential PPV vectors found. Other known PPV vectors were present in much lower specimen numbers in the following decreasing order: Hyalopterus pruni (Geoffroy), Phorodon humuli (Schrank), Brachycaudus helichrysi (Kaltenbach), Myzus persicae (Sulzer), Brachycaudus cardui (Linnaeus), Aphis gossypi Glover, Macrosiphum rosae (Linnaeus) and Metopolophium dirhodum (Walker). During all 3 years, statistically significantly greater number of known PPV vectors were captured on the plum trees during the spring peaks compared to the autumn peaks. The number of known PPV vectors captured during the spring peaks on the plum trees was also significantly larger than the number of known vectors captured on the apricot trees.

Genetic Resource of the Resistance of Vicia faba L. against the Black Bean Aphid, Aphis fabae Scopoli

The Black bean aphid Aphis fabae Scopoli (Homoptera: Aphididae) is a serious pest of faba bean, Vicia faba L. (Fabaceae) in Algeria. The use of resistant cultivars may reduce the impact of this pest on broad bean production and at the same time reduce environmental risks and control costs. The level of resistance of fourteen cultivars of broad bean, Vicia faba was screened in the field against the main aphid pest of faba bean, the Black bean aphid, Aphis fabae Scopoli during January to April 2011 in Biskra region (in the east of Algeria). Among the cultivars tested, six cultivars (1, 9, 12, 13, 14 and 15) were the most resistant in the three counts, while three cultivars (4, 6 and 11) were showed a high susceptibility against this aphid at least once. The remainder of cultivars (3, 5, 7, 8 and 10) revealed an unsettled level of resistance. The relationship between the level of resistance and morphological characters of cultivars indicated that the resistant cultivars have a longer leaflet than the high susceptible cultivars. In the other hand, the statistical analysis showed that no significant differences on the plant height and the leaflet width in the tow category of cultivars (resistant and high susceptible).

Susceptibility of Five Sugar Beet Cultivars to the Black Bean Aphid, Aphis fabae Scopoli (Hemiptera: Aphididae).

The black bean aphid, Aphis fabae Scopoli (Hemiptera: Aphididae), is one of the important pests of sugar beet. The relative impact of resistance, including antibiosis and antixenosis of five sugar beet cultivars (Doroti, Perimer, Pershia, Rozier and 006) on A. fabae was studied under laboratory conditions using clip cages. The antibiosis test was based on life table parameters. Significant differences on developmental time, mean number of nymphs/aphid/day, fecundity, and adult longevity of A. fabae were found across tested sugar beet cultivars. In addition, there were significant differences among the sugar beet cultivars for population growth parameters such as the intrinsic rate of natural increase (r m ), net reproductive rate (R 0), finite rate of increase (λ), doubling time (DT), and mean generation time (T) of A. fabae. The highest and lowest (r m ) values were observed on Pershia (0.449 nymphs/female/day) and Perimer (0.358 nymphs/female/day), respectively. No significant differences were found for the preference of the black bean aphid, and antixenosis had no effect on resistance against this aphid. As a result, our findings showed that the Pershia cultivar was a relatively susceptible host plant. Two cultivars (Perimer and Rozier) were relatively resistant to A. fabae, which could prove useful in the development of IPM programs for this aphid in sugar beet fields.

Lethal and sublethal effects of three insecticides on the aphid parasitoid, Lysiphlebus fabarum Marshall (Hymenoptera: Aphidiidae)

Lysiphlebus fabarum Marshall is the main parasitoid of the black bean aphid, Aphis fabae Scopoli. Lethal and sublethal effects of insecticides, thiacloprid+deltamethrin, pirimicarb and pymetrozine were evaluated on the parasitoid under laboratory conditions. One-day-old mummies were exposed to the recommended field concentration of either insecticides via dipping method. Adult emergences were reduced by 82.67, 19.98 and 10.67 % for thiacloprid+deltamethrin, pirimicarb and pymetrozine treatments, respectively. Thiacloprid+deltamethrin had the most adverse effect on the fecundity of the emerged females, while pirimicarb and pymetrozine did not have such effects. According to International organization for biological control (IOBC) insecticide toxicity classification, thiacloprid+deltamethrin resulted to be moderately harmful (E = 97.39%), whereas pirimicarb (E = 15.78%) and pymetrozine (E = 5.15%) were harmless. Thiacloprid+deltamethrin negatively affected five of the estimated demographic parameters (GRR, R0 , rm, λ and T ). Pirimicarb negatively affected GRR, R0 and T, while it had no adverse effects on rm and λ. None of the studied demographic parameters were affected by pymetrozine. Our results suggest that pirimicarb and pymetrozine can be considered as safe for L. fabarum, but that thiacloprid+deltamethrin can have serious detrimental of this parasitoid in the field.

Effect of temperature on biological parameters of Aphidius matricariae, the Aphis fabae parasitoid

Aphids can have devastating effects on agriculture and horticulture, and biological control agents form an important means of controlling them. Aphidius matricariae Haliday is an important endoparasitoid for the suppression of aphid pest population outbreaks. In this research, the influence of three different temperatures, 20, 25 and 30°C, on some life cycle charactersitic of A. matricariae was studied under laboratory conditions when present on its host, Aphis fabae Scopoli. At 30°C, the intrinsic rate of increase, net reproductive rate, finite rate of increase, mean generation time and increase rate in one week were all significantly lower compared to the lower temperatures. The results showed that temperature had a significant effect on the duration of parasitoid development from oviposition to adult emergence. Moreover, the value of doubling time was higher at 30°C than at 20 and 25°C. The parasitoid had the shortest longevity, life span and lowest fecundity at 30°C. This investigation of temperature-dependent development and reproduction can help in the management of biological control programs. The results of this study demonstrate that A. matricariae is able to perform, and be mass produced, as a favorable and proper natural enemy for the biocontrol of A. fabae at a temperature range of 20-25°C.

Structure of the Black Bean AphidAphis fabae(Hemiptera: Aphididae) Complex, Inferred from DNA Barcoding

The black bean aphid, Aphis fabae Scopoli is a polyphagous aphid causing significant damage to several cultivated and uncultivated plants. In the present work, we have used COI barcoding to distinguish between three subspecies of A. fabae, frequently found in Tunisia, namely A. f. fabae, A. f. solanella and A. f. cirsiiacanthoidis. Results of our study revealed that COI barcoding was efficient to generate haplotypes discriminating A. f. fabae from the two remaining subspecies. Indeed, among seven haplotypes, identified and named H1–H7, five were found exclusively in A. f. fabae, one represented exclusively A. f. cirsiiacanthoidis, and one was shared by A. f. cirsiiacanthoidis and A. f. solanella. However, the differentiation of Aphis f. fabae from A. f. solanella and A. f. cirsiiacanthoidis was not further supported by a phylogenetic distinction, as it was revealed by neighbour-joining and maximum parsimony phylogenies. Such a coherent genetic structure of the A. fabae complex, not governed by the subspecies factor, as inferred from our present mitochondrial (mt)DNA data, is in agreement with previous analyses based on genomic DNA. Therefore, we hypothesize that the phenotypical and physiological processes having led to differentiation between subspecies would have arisen from weak selection pressures, thus resulting in little genetic change between subspecies. In combination with additional still-to-come data from additional markers, results of this study will be important to constitute a groundwork for pest integrated management.

Preference of two populations of Propylea quatuordecimpunctata (Coleoptera: Coccinellidae) for Aphis fabae and Aphis gossypii (Homoptera: Aphididae)

Prey preference of natural enemies is an important parameter used in studies on their efficiency. Feeding preferences of individuals from two populations of Propylea quatuordecimpunctata (L.) (Coleoptera: Coccinellidae) for the essential prey items, Aphis fabae Scopoli, 1763 and Aphis gossypii Glover, 1877 (Homoptera: Aphididae) were evaluated in the laboratory using Manly's β preference index (β). For the predator preference experiment, equal numbers of A. fabae and A. gossypii were offered to the predator. The experiment was conducted on a broad bean leaf disc with 20 replicates. After 24 h, the unconsumed aphids were counted. Individuals of P. quatuordecimpunctata from both populations consumed more A. gossypii [Karaj population (mean ± SE): 28.15 ± 1.04 and Sari population 34.35 ± 0.51] than A. fabae (Karaj population: 17.95 ± 0.64 and Sari population: 17.7 ± 1.01). The values of Manly's β preference index (β) for A. gossypii were 0.73 ± 0.01 and 0.77 ± 0.01 for the Karaj and Sari populations, respectively and for A. fabae were 0.26 ± 0.01 and 0.22 ± 0.01 for the Karaj and Sari populations, respectively. Comparison of the preference indices using a t-test revealed significant differences between the prey preferences of those from the Sari population (t = 22.53, df = 38, P < 0.0001) and the Karaj population (t = 26, df = 38, P < 0.0001). These results reveal that P. quatuordecimpunctata from the two populations prefer A. gossypii over A. fabae.

The cost of ant attendance and melezitose secretion in the black bean aphid Aphis fabae

1. The aphid Aphis fabae (Scopoli) is facultatively tended by Lasius niger (Linnaeus) ants. Previously, we found that A. fabae colonies can be made up of several clones, and that clones display significant differences in the composition of their honeydew sugars, especially in the amount of the ant attractant sugar melezitose that they produce.2. These clonal differences could greatly impact the strength of the mutualistic interaction with ants as well as the aphids' fitness.3. Hence, the aim of this study was to compare the fitness of different A. fabae clones that differed in their melezitose secretion, and whether or not they were tended by ants.4. Individual fitness indices, colony growth, and alate production of single‐clone aphid colonies were analysed.5. The results demonstrate that the fitness consequences of ant attendance critically depend on an interaction between levels of melezitose production. In particular, we show that high‐melezitose secreting clones produce fewer alates and hence might have a lower dispersal ability in the presence of ants.6. Furthermore, these data confirm previous evidence that ant attendance is costly and results in the production of fewer apterae.

Comparison of the demographic parameters and survival of two phenotypes of Harmonia axyridis (Coleoptera: Coccinellidae)

This paper reports the results of a comparative study of the demographic parameters of two phenotypes of Harmonia axyridis Pallas, reared on the black bean aphid, Aphis fabae Scopoli at 25 &plusmn; 1&deg;C, 65 &plusmn; 2% RH and a photoperiod of 16L : 8D. The values of the intrinsic rate of increase and the finite rate of increase, which were obtained by bootstrapping, were greater for the succinea morph (0.182 females/female/d and 1.200, respectively) than the spectabilis morph (0.168 females/female/d and 1.183, respectively). The net reproductive rates and mean generation times of the two morphs did not differ. The risk of death of the succinea morph was significantly greater. However, there was no significant difference between the estimated survival times. Mean survival times were 95.2 d and 89.3 d for the spectabilis and succinea morphs, respectively.

Esterase profile changes in ladybeetle, &lt;i&gt;Hippodamia variegata&lt;/i&gt; Goeze (Coleoptera: Coccinellidae) and its prey, &lt;i&gt;Aphis fabae&lt;/i&gt; Scop. (Homoptera: Aphididae) affected by two insecticides, thiamethoxam and pirimicarb

Black bean aphid, Aphis fabae Scopoli (Homoptera: Aphididae), is a cosmopolitan and serious pest of diverse plant species. In addition to inflicting direct damage, it is an important vector of viruses producing indirect damages. Hippodamia variegata , is considered as aphids predator both in their larval and adult stages. Thus, the aim of the current study was to investigate toxicological, biochemical and physiological effects of two widespread used pesticides against aphids including pirimicarb and thiamethoxam on third instar larvae of the ladybeetle and the adult female of the aphid in laboratory condition. Bioassay showed that LC 50 value in thiamethoxam treatment against A. fabae and H. variegata was 113.85 and 788.55 mg (ai)L -1 , respectively and LC 50 value for pirimicarb treatment against two insects was 2.94 and 2740.07 mg (ai)L -1 , respectively. Enzyme assays showed that AChE and CbE (evaluated by a -NA) of A. fabae inhibited significantly by pirimicarbtreatments(P>0.05), whilst thiamethoxam treatment did not affect both enzymes. Both insecticides did not affect H. variegata AChE and CbE activities, significantly. Polyacrylamide gel electrophoresisof general esterases of A. fabae by a solution mixture of both substrates ( a - and b -NA) showed that only one band present in the control and in the treated insects. However, in H. variegata larvae, there were four esterase isoforms in the control and the isoforms showed changes after insect treatment with the insecticides. Thus it is concluded that susceptibility of the two insects toward the two insecticides are different and these differences were obvious in their enzyme activity and their isoforms as well.

Effect of temperature and prey in the biology of Scymnus subvillosus

Scymnus subvillosus (Goeze) (Coleoptera: Coccinellidae) is an aphidophagous predator present in the Azores (Portugal), but occurring at low densities. Scymnus species belong to a poorly known Coccinellidae group of biological control agents. In this study we aimed to evaluate the suitability of Myzus persicae (Sulzer), Aphis fabae Scopoli and Melanaphis donacis (Passerini) (Homoptera: Aphididae) as prey for S. subvillosus. To achieve this, we determined (i) the temperature and prey-dependence for development and survival of the immature stages, (ii) the prey-dependence for reproductive performance at 25 °C and (iii) the voracity and nutritional physiology of the 4th larval instar fed on A. fabae. The development time from first instar larva to adult decreased with increasing temperature, ranging from 61.5 days at 15 °C to 10.4 days at 30 °C. To complete immature development on M. donacis, the lower development threshold (LDT) was estimated to be 11.7 °C and the sum of effective temperatures (SET) to be 196.3 degree-days (DD). At 15 °C, larvae failed to develop when fed on A. fabae or M. persicae but on M. donacis 22 % of the larvae survived. We also found that development time of immature stages was prey-dependent, with M. persicae being the least suitable prey. The reproductive parameters were prey-dependent, with A. fabae and M. donacis allowing better performance than M. persicae. Twelve-hour-old 4th instars of S. subvillosus ingested 3.23 mg of biomass per day corresponding to an average of 10.5 aphids of A. fabae, allowing for a daily mean weight gain of 0.71 mg. The conversion efficiency and relative growth rate obtained were approximately 21 and 48 %, respectively. The results obtained in the present study suggest that both A. fabae and M. donacis are more suitable prey for development and reproduction of S. subvillosus than M. persicae.