Laboratory study of cannibalism and interspecific predation in ladybirds

Abstract.

• 1 In the absence of aphids, adult females of Adalia bipunctata (L.) showed a greater reluctance to eat eggs than males.
• 2 Eggs and young larvae were more vulnerable to cannibalism than older larvae and starved larvae were more vulnerable than well-fed larvae.
• 3 Both egg and larval cannibalism is inversely related to the abundance of aphids.
• 4 Eggs are a better food, in terms of larval growth and survival, than aphids.
• 5 In the absence of aphids interspecific predation occurred, but not equally, between the coccinellids A.bipunctata, A.decempunctata (L.), Coccinella septempunctata L. and C.undecempunctata L.
• 6 Larvae and adults of A. bipunctata and C.septempunctata were reluctant to eat conspecific eggs painted with a water extract of the other species' eggs and larvae of C. septempunctata were more likely to die after eating a few eggs of A.bipunctata than vice versa.
• 7 These results indicate that cannibalism occurs mainly when aphid prey is scarce and is adaptive in that it improves the chances of survival, and coccinellids, to varying degrees, are defended against interspecific predation.

     

Effects of an invading coccinellid on native coccinellids in an agricultural landscape

Seven native coccinellid species inhabited alfalfa, corn, and small grain fields in eastern South Dakota prior to invasion and establishment of Coccinella septempunctata L. Six species occurred in all crops, however, Adalia bipunctata (L.) occurred only in corn. The structure of native coccinellid communities differed significantly for years prior to compared with years after establishment of C. septempunctata in fields of the three agricultural crops. Differences in community structure were accounted for mainly by reduced abundance of two species, C. transversoguttata richardsoni Brown and Adalia bipunctata (L.). Annual abundance of C. transversoguttata richardsoni averaged 20–32 times lower during post-invasion years than in years prior to invasion, depending on crop; while annual abundance of A. bipunctata averaged 20 times lower in corn after invasion. Addition of C. septempunctata to the community did not result in a significant increase in total abundance of coccinellids in the crops. Coccinellid abundance in agricultural crops may be limited by the total abundance of prey or by the availability of other requisites in the landscape as a whole. Therefore, introduction of a new species, while resulting in reductions in native species populations, may not increase total coccinellid abundance, and may therefore have no net effect on biological control of aphid pests.     

Effects of mixed prey on the development and demographic attributes of a generalist predator,Coccinella septempunctata (Coleoptera: Coccinellidae)

Coccinella septempunctata Linnaeus, 1758 (Coleoptera: Coccinellidae) is an aphidophagous ladybird beetle species with cosmopolitan distribution. However, it may also thrive on arthropods other than aphids, when the latter are not readily available. Certain life history traits and demographic attributes of C. septempunctata were determined using seven different diets with different alternations and proportions of an aphid, Lipaphis erysimi (Kaltenbach,1843) and a mite, Tetranychus urticae Koch, 1836, in the laboratory (at 25±0.5°C, 65±5% RH and a photoperiod of 16 h L:8 h D).The larval duration was longest (12.61±6.17 days) when fed an alternating diet of two days aphid/two days mite. Adult longevity was longest (78.65±1.09 days) when fed aphids only and shortest (3.17±1.25 days) when fed mites only. Life expectancy (e_x) was highest (111 days) when adults were fed only aphids and lowest (11.3 days) when fed only mites. Survival rates of ladybird beetles were positively related to an increasing ratio of aphids in their diet. Their ability to prey on both aphids and mites indicates the effectiveness of C. septempunctata as a biological control agent on plants infested with these two pests.     

Assessment of patch quality by ladybirds: role of larval tracks

Gravid females of the two-spot ladybird, Adalia bipunctata (L.), were deterred from ovipositing when kept in petri dishes that had previously contained conspecific larvae but not conspecific adults, or the larvae of another two species of ladybird, Adalia decempunctata (L.) and Coccinella septempunctata L. The deterrent effect was density dependent and mediated via a chloroform-soluble contact pheromone present in the larval tracks. Similarly, gravid females of C. septempunctata were deterred from ovipositing by conspecific larval tracks and chloroform extracts of these tracks, but not by the tracks or extracts of tracks of A. bipunctata larvae. That is, in ladybirds the larvae produce a species-specific oviposition-deterring pheromone. In the field, the incidence of egg cannibalism in ladybirds increases very rapidly with the density of conspecific eggs or larvae per unit area. Thus, in responding to the species specific oviposition deterring pheromone female ladybirds reduce the risk of their eggs being eaten and spread their offspring more equally between patches. Received: 14 March 1997 / Accepted: 26 August 1997     

Stage and age-specific predation in four aphidophagous ladybird beetles

In the present study, stage- and age-specific predatory patterns and nutritional ecology attributes of four co-occurring aphidophagous ladybirds, namely, Coccinella septempunctata (L.), Coccinella transversalis F., Cheilomenes sexmaculata (F.) and Propylea dissecta (Mulsant) on pea aphid, Acyrthosiphon pisum (Harris) were investigated. Despite their lower consumption rates, smaller ladybirds (C. sexmaculata and P. dissecta) and earlier instars were efficient converters of aphid prey with higher relative growth rates, over the respective larger ladybirds (C. septempunctata and C. transversalis) and fourth instars. The consumption rates of pea aphids by the larvae increased with stage, but with a decline in the later part of the fourth instars, just prior to pupation. Adult females of early age groups (between 2 and 7 days) had higher consumption rates than later age groups in all the four species. Further in adult females, consumption rates decrease with increase in age, but without significant changes in conversion efficiencies and relative growth rates.     

INFLUENCE OF TEMPERATURE ON CERTAIN BIOLOGICAL ATTRIBUTES OF A LADYBEETLE COCCINELLA SEPTEMPUNCTATA LINNAEUS

Influence of temperature on certain biological attributes of an aphidophagous ladybeetle, Coccinella septempunctata Linnaeus, feeding on mustard aphid, Lipaphis erysimi (Kaltenbach), at five different temperatures, viz. 20, 25, 27, 30 and 35°C was investigated. Its developmental period was shortest (11.7 ± 0.09 days) at 35°C and longest (20.6 > 0.35 days) at 20°C. Developmental rate increased with increase in temperature. Hatching percent, larval survival, adult emergence and growth index were maximum at 30°C and minimum at 20°C. Oviposition period and fecundity were highest at 30°C and lowest at 20°C. A positive linear relationship exists between temperature and developmental rate and negative correlation between the duration of immature life stages and temperature. The proportion of developmental period allocated to each immature stage was found to be similar at each temperature regime. Thus, 30°C was found as the most suitable for C. septempunctata amongst the five temperatures tested.     

Toxicity of plant essential oil vapours to aphid pests and their coccinellid predators

The comparative toxicity of five essential oil vapours was tested against four aphid species, the black bean aphid Aphis fabae, the pea aphid Acyrthosiphon pisum, the chrysanthemum aphid Macrosiphoniella sanborni, the green peach aphid Myzus persicae and on two of the most common coccinellid predators, the seven-spotted ladybird Coccinella septempunctata and the two-spotted ladybird Adalia bipunctata. All essential oils were highly toxic to the aphid species tested with LC₅₀ and LC₉₉ values ranging between 0.17 and 1.92 and 0.44 and 4.83 µL/L air, respectively, depending on the aphid species and on the essential oil. Coccinellid predators were also highly susceptible to the essential oil vapours and the selective toxicity ratio varied depending on aphid species, coccinellid predator and essential oil. The possibilities for the utililization of essential oils as aphicides, especially in IPM programmes in glasshouses are discussed with regard to the present findings.     

Effects of food and temperature on development,fecundity and life‐table parameters of Adalia bipunctata (Coleoptera: Coccinellidae)

Development, reproduction and life tables of Adalia bipunctata (L.) were studied at three temperatures (19, 23 and 27°C) on a mixture of frozen pollen and Ephestia kuehniella Zeller eggs as a factitious food and on the aphids Myzus persicae (Sulzer) and Acyrthosiphon pisum (Harris) as natural foods. Development time of A. bipunctata on all tested diets decreased with increasing temperature. Mortality was lowest at 23°C, averaging 44.5%, 42.6% and 24.3% on factitious food, A. pisum and M. persicae respectively. The shortest developmental time from egg to adult at this temperature was observed on factitious food (18.55 days). However, the factitious food was inferior to the aphid diets in terms of reproduction, yielding the longest pre‐oviposition period, shortest oviposition period and lowest fecundity. The mean oviposition rate at 23°C varied from 19.94 to 25.03 eggs day^?1 on factitious food and M. persicae respectively. The intrinsic rate of increase (r_m) on different foods increased with increasing temperature and ranged from a minimum of 0.08 females/female/day on factitious food (19°C) to a maximum of 0.18 females/female/day on A. pisum (27°C). The results suggest that a mixture of E. kuehniella eggs and pollen fully support development of A. bipunctata larvae and can be used as an alternative to live aphids in the mass rearing of the pre‐imaginal stages of the predator. However, reproductive performance of a laboratory population may be better on aphids than on the factitious food.     

Evaluation of four co-occurring ladybirds for use as biocontrol agents of the pea aphid,Acyrthosiphon pisum (Homoptera: Aphididae)

The potential of four co-occurring ladybirds, Coccinella septempunctata (L.), Coccinella transversalis (F.), Cheilomenes sexmaculata (F.), and Propylea dissecta (Mulsant), as predators of the pea aphid, Acyrthosiphon pisum (Harris) was investigated. Larger ladybirds were more voracious while smaller ones had higher consumption indices and were more efficient converters of food.     

The influence of time and temperature on molecular gut content analysis： Adalia bipunctata fed with Rhopalosiphum padi

Gut content analysis is a useful tool when studying arthropod predator-prey interactions. We used polymerase chain reaction （PCR） technique to examine how detection of prey DNA in the gut content of predators was influenced by digestion time and temperature. Such knowledge is critical before applying PCR-based gut content analysis to field collected predators. Larvae of the two-spotted ladybeetle （Adalia bipunctata L.） were fed with the bird cherry-oat aphid （Rhopalosiphum padi L.） at either 21℃ or 14℃. After consuming one aphid, the predators were allowed to digest the prey for a range of time periods up to 24 hours. The influence of temperature on A. bipunctata feeding behavior was also recorded. From the fed larvae, total DNA was extracted and PCR reactions with R. padi specific primers were run. The number ofA. bipunctata that tested positive for R. padi DNA was negatively related to the length of digestion time. Temperature influenced larval feeding behavior but did not have a significant effect on R. padi DNA detection. After pooling the data from both temperature treatments we estimated the time point when R. padi DNA could be amplified from 50% of the fed A. bipunctata by PCR to be 4.87 hours. With such a rapid decrease in prey DNA detection success, positive PCR reactions will most likely be the result of predation events occurring shortly before capture. If a defined digestion temperature range has proven not to influence prey detection, PCR data obtained from predators collected within that particular range can be interpreted in the same way.     

Interspecific variation in the escape responses of aphids: effect on risk of predation from foliar-foraging and ground-foraging predators

A series of laboratory experiments was conducted to determine the effect of interspecific differences on prey defensive behavior on the susceptibility of two aphid species (Acyrthosiphon pisum and A. kondoi) to a ground-foraging predator, Harpalus pennsylvanicus, and a foliar-foraging predator, Coccinella septempunctata. These organisms are representative of a biologically and economically important predator/prey system in alfalfa. The primary defensive behavior of both aphid species toward C. septempunctata was to “drop” from the plant. Both aphid species were significantly more likely to drop from the plant in the presence of C. septempunctata. However, when C. septempunctata was present, a significantly lower proportion of A. kondoi individuals dropped (0.42 ± 0.07) compared to A. pisum (0.73 ± 0.08). As a result of their lower propensity to drop from the plant A. kondoi individuals are significantly more likely to be consumed by C. septempunctata. Conversely, the higher propensity of A. pisum individuals to drop increased their susceptibility to ground-foraging predators. When A. pisum was the prey species, ground-foraging predators made a significant contribution to overall aphid suppression and there was a significant synergistic interaction between ground and foliar-foraging predators. When A. kondoi was the prey there was no interaction between the predator species. As either a cause or consequence of its higher propensity to drop, A. pisum seems to be more adapted for survival and dispersal off the plant. In comparison to A. kondoi individuals, A. pisum individuals relocate plants more quickly (63 ± 41 s vs. 164 ± 39 s), disperse farther (18 ± 1.7 cm vs. 13 ± 0.66 cm), and survive longer (37 ± 2.0 h vs. 25 ± 2.0) off the plant. This study demonstrates the importance of prey defensive behavior in determining the susceptibility of a prey species to a multiple-predator complex. Received: 24 February 1997 / Accepted:17 December 1997     

Biological Parameters for Four Coccinellid Species in Central Saudi Arabia

Developmental and reproductive rates ofAdonia variegataGoeze,Coccinella novemnotataHerbst,C. septempunctataL., andC. undecimpunctataL. were studied in wheat and barley in Central Saudi Arabia. Beetles were reared in the laboratory at 25 ± 2°C onBrevicoryne brassicae(L.) andRhopalosiphum padiL.A. variegataandC. undecimpunctatahad significantly higher egg hatching (X = 81.8 and 74.5%), adult longevity (X = 71.8 and 70.0 days), and survival (X = 61.8 and 61.5%), respectively.Coccinella undecimpunctatahad the highest fecundity (X = 370.5 eggs/female) and longest oviposition period (X = 29.8 days).C. septempunctataexhibited the lowest values for these biological parameters. No differences were evident in the total developmental time or egg and pupal duration, although species differences occurred in the larval duration. Larvae ofA. variegatadeveloped faster (X = 11.8 days) than Larvae ofC. septempunctata(X = 12.0 days),C. undecimpunctata(X = 12.2 days), orC. novemnotata(X = 13.1 days). The intrinsic rate of increase (r_m) and predicted population density were higher forC. undecimpunctata(X = 0.093 and 98553) after 60 days than forC. novemnotata(X = 0.088 and 59405),C. septempunctata(X = 0.086 and 35033), orA. variegata(X = 0.082 and 37991), respectively.     

The potential of predators in natural control of aphids in wheat: Results of a ten-year field study in two German landscapes

In the present study, we investigated the natural control of aphids by predators in wheat fields in a low (L) and high-input cropping region (H) of Germany during a 10-year period. Data for the statistical analyses were obtained from weekly after the start of aphid emergence. The mean annual aphid indices, calculated as the sum of Sitobion avenae (Fabr.), Rhopalosiphum padi (L.), Metopolophium dirhodum (Walk.)(Homoptera: Aphididae), were 30.4 and 81.5 × 103 aphid days per m2, for L and H, respectively. Nine predator fractions were analysed: Coccinella septempunctata L., adults (1) and larvae (2), Propylea quatuordecimpunctata (L.) (Coleoptera: Coccinellidae) adults (3) and larvae (4), syrphid larvae (mostly Episyrphus balteatus [De Geer] (Diptera: Syrphidae)) (5), Chrysoperla carnea Steph. (Neuroptera: Chrysopidae) larvae (6), and adult carabids (7), staphylinids (8) and spiders (9). The two sites were comparable in terms of the mean size of the overall predator community, expressed in predator units (PU): 4.9 PU/m2 (L) vs. 5.4 PU/m2 (H). Most predator fractions responded numerically to increasing aphid densities. The numerical response was strongest in syrphid larvae, scarcely detectable in adult coccinellids, and virtually non-existent in epigeic arthropods. Multiple regression models revealed indirect relationships between the weekly overall predator community densities (PU/m2) and individual predator fractions (individuals/m2) and absolute rates of aphid density increase (individuals/m2) one or two weeks after baseline. A site-independent reduction of the aphid density increase to nil (y = 0) was observed at 3.9 to 4.2 PU/m2. Consequently, the 2.7 times higher aphid density at H cannot be attributed to the presence of fewer predators or lower effects of the overall predator community or of any individual predator fraction.     

The effects of thirteen species of aphids on some life history parameters of the ladybird Coccinella septempunctata

The prediction of impact ofcoccinellids in an aphid infested crop dependson the food specificity of the predator. Theresponse towards thirteen species of aphids(Sternorrhyncha: Aphididae) was thereforetested in the most abundant aphidophagouscoccinellid Coccinella septempunctata L.(Coleoptera: Coccinellidae). All aphidspecies studied (Eucalipterus tiliae(L.), Tuberculatus annulatus (L.), Euceraphis betulae (L.), Cavariellakonoi Takahashi, Liosomaphis berberidis(Kaltenbach), Acyrthosiphon ignotumMordvilko, Aphis spiraephaga Müller,Aphis fabae Scopoli, Macrosiphoniella artemisiae Boyer de Fonscolombe, Capitophorus hippophaeus(Walk.), Acyrthosiphon pisum (Harris),Aphis craccivora Koch, Sitobionavenae (Fabricius) were suitable foodaccording to the rate of larval development,larval mortality and adult fresh weight.Females of C. septempunctata fed with A. pisum and S. avenae laid twice as manyeggs as those fed with A. fabae and A. craccivora. These data are needed foreffective mass rearing of the studiedcoccinellid species.     

Effect of temperature on development, growth and feeding of Coccinella septempunctata and Hippodamia convergens reared on the tobacco aphid, Myzus persicae nicotianae

Preimaginal development, mortality, aphid consumption rate, and size and weight upon reaching the adult stage of the aphidophagous coccinellids Hippodamia convergens Guérin-Méneville and Coccinella septempunctata L. collected from Karditsa, central Greece, were examined at four constant temperatures (14, 17, 20 and 23 °C) and L16:D8. The coccinellids fed on the tobacco aphid, Myzus persicae nicotianae Blackman. Egg, larval and pupal mortality was highest at 14 °C reaching 85.0, 73.8 and 29.4% in H. convergens and 49.3, 75.4 and 58.8% in C. septempunctata, respectively. Total preimaginal development ranged from 57.2 to 70.4 days at 14 °C, and to 16.9 and 22.1 days at 23 °C in H. convergens and C. septempunctata, respectively. Heavier and larger adults of H. convergens were obtained at 17 and 20 ° C. In C. septempunctata temperature did not affect adult weight while the lowest size was observed at 14 and 17 °C. Day-degrees requirements for preimaginal development in H. corvengens were 212.9 above a developmental threshold of 11.0 °C. The corresponding values for C. septempunctata were 281.5 and 10.7 °C. In H. convergens total and daily aphid consumption ranged from 46.8 aphids at 14 °C to 85.0 aphids at 23 °C and from 1.5 aphids at 14 °C to 9.2 aphids at 23 °C, respectively. The corresponding values for C. septempunctata were 112.0 and 2.7 at 14 °C and 157.7 and 12.4 at 23 °C. The results show the high potential of both predators as biological control agents against the tobacco aphid. The knowledge obtained could be essential for their appropriate use and for the improvement of mass rearing systems.     

Abundanzdynamik von getreideblattläusen (Hom., aphididae) und ihrer natürlichen antagonisten an verschiedenen weizensorten in deir ezzor (Syrische Arab. Rep.)∗

Im Jahre 1990 wurden Freilanderhebungen zur Abundanzdynamik von Getreideblattläusen und ihrer Antagonisten in verschiedenen Weizenbeständen und ‐Sorten in Hammar‐alkassra bei Deir Ezzor (Syrische A.R.) durchgeführt.

Die Besiedlung der Pflanzen durch die Blattlausarten Sitobion avenae (F.), Rhopalosiphum padi (L.) und Metopolophium dirhodum (Walk.) begann zum Schossen des Weizens. Ihr Abundanzmaximum trat zum Ende des Ährenschiebens/Beginn der Blüte ein. Danach brach die Population schnell zusammen.

Unter den spezifischen Prädatoren waren die Coccinellidae, insbesondere die Arten Coccinella septempunctata L. und Adalia bipunctata (L.), in den Beständen kontinuierlich nachzuweisen. Vertreter der Familien Syrphidae und Chrysopidae erreichten in den Weizenbeständen sehr geringe Dichten. Die Parasitierungsrate der Blattläuse (Mikrohymenopteren und entomopathogene Pilze) variierte zwischen 7 % und 17 % bezogen auf die Aphidenpopulation.

Die Ergebnisse ließen eine Bevorzugung der Weizensorte “Gesira 17”; gegenüber der Sorte “Maxiki”; durch die Aphiden erkennen. Eine gezielte Bekämpfung der Blattläuse müßte anhand vorliegender Resultate zum Ende der Schoßphase des Weizens (DC 35/40), Anfang bis Mitte April, erfolgen.

Zukünftige Untersuchungen sollen in erster Linie klären, ob ein hoher Befall durch Aphiden zu Ertragseinbußen führt. Dazu macht es sich erforderlich, die Abundanzdynamik der Blattläuse und ihrer Gegenspieler zu untersuchen und darauf aufbauend Befall‐Schadens‐Beziehungen abzuleiten, um somit im Bedarfsfall ökonomisch und ökologisch gerechtfertigte Bekämpfungsmaßnahmen durchführen zu können.     

Selection of aphid prey by Adalia bipunctata L. and Coccinella 7-punctata L

Larvae and adults of Adalia bipunctata L. and Coccinella 7-punctata L. seemed unable to detect and avoid feeding on unsuitable or toxic aphids, e.g. larvae of A. bipunctata fed on the highly toxic Megoura viciae, even when given the choice of a suitable aphid. Apparent preferences were not always for the most suitable food. Field cage experiments demonstrated the preference of adult A. bipunctata and C. 7-punctata for different habitats, the former ovipositing at the shrub level (4 ft.) and the latter feeding and ovipositing on plants near ground level.     

Effects of a microsporidium from the convergent lady beetle, Hippodamia convergens Guérin-Méneville (Coleoptera: Coccinellidae), on three non-target coccinellids

A microsporidium from Hippodamia convergens was transmitted horizontally to three non-target coccinellid hosts (Adalia bipunctata L., Coccinella septempunctata L. and Harmonia axyridis Pallas) under laboratory conditions. For all species examined, microsporidia-infected larvae took significantly longer to develop than did uninfected larvae but the microsporidium had no effect on larval mortality. Adult sex ratios of uninfected and microsporidia-infected adults were about 1:1 (♀:♂) and did not differ significantly. At the end of a 90-day trial, microsporidia-infected H. convergens produced significantly fewer eggs and did not live as long as uninfected individuals. Differences in fecundity and longevity were not observed for the three non-target coccinellids that were examined. Mean spore counts from smear preparations of microsporidia-infected A. bipunctata did not differ significantly from H. convergens, suggesting that A. bipunctata (a native coccinellid) is a suitable host for the microsporidium but infection was lighter in C. septempunctata and H. axyridis (introduced species). Vertical transmission of the pathogen was observed during the 90-day trial by examining eggs and larvae that were produced by microsporidia-infected adults. For all species examined, 100% vertical transmission of the pathogen was eventually observed. Three eugregarines were found in two adult A. bipunctata: Gregarine A trophozoites are similar in size to those of Gregarina katherina Watson (described earlier from Coccinella spp.), Gregarine B trophozoites are similar in size to those of Gregarine A but are morphology distinct, and Gregarine C trophozoites are similar in size to G. barbarara Watson (described earlier from A. bipunctata).     

Interactions between the fungal pathogen Beauveria bassiana and three species of coccinellid: Harmonia axyridis, Coccinella septempunctata and Adalia bipunctata

Harmonia axyridis is a predatory coccinellid, native to central and eastern Asia. It has been available in many countries for use as a biological control agent of pest aphids and scale insects. In many of these countries, including the USA, H. axyridis has established. It is now considered an invasive alien species for a number of reasons, including its impact on functional biodiversity. Beauveria bassiana is known to be a natural mortality agent of overwintering coccinellids and is a potential candidate for the biological control of H. axyridis. In this paper we compare the susceptibility of three species of coccinellid, H. axyridis (cultures derived from Japan and UK), Coccinella septempunctata and Adalia bipunctata to infection by B. bassiana (commercial strain GHA) after exposure at three doses (10⁵, 10⁷, 10⁹ conidia ml⁻¹). The two subpopulations of H. axyridis (Japan and UK) were more resistant to B. bassiana infection than either A. bipunctata or C. septempunctata. This is exemplified by the median lethal doses at 10 days post-inoculation (LD₅₀) of 10^6.2, 10^6.0, 10^8.3, 10^9.6 conidia ml⁻¹ for A. bipunctata, C. septempunctata, H. axyridis (Japan) and H. axyridis (UK), respectively. Only doses of 10⁹ conidia ml⁻¹ resulted in mortality of H. axyridis, in contrast, 80% of C. septempunctata and 70% of A. bipunctata exposed to 10⁷ conidia ml⁻¹ of B. bassiana succumbed to infection. The fecundity (cumulative mean egg production over 10 days) of A. bipunctata and H. axyridis (UK) was also assessed. The fecundity of C. septempunctata could not be assessed because this species requires diapause prior to the onset of reproduction and these studies were on beetles that had recently eclosed (2–8 weeks). Harmonia axyridis (Japan) produced no eggs in most treatments including the control and so was excluded from analysis. High dose (10⁹ conidia ml⁻¹) inoculation reduced the fecundity of A. bipunctata to zero but egg production was similar for individuals inoculated with doses of 10⁵, 10⁷ conidia ml⁻¹ and control individuals. In contrast, all doses of B. basssiana reduced H. axyridis (UK) egg production dramatically. We discuss these results in relation to the potential for control of H. axyridis using B. bassiana.     

Do Chrysoperla carnea and Adalia bipunctata influence the spread of Cucurbit aphid‐borne yellows virus and its vector Aphis gossypii?

The effects of two aphidophagous predators, the larvae of Chrysoperla carnea and the adults of Adalia bipunctata, on the spread of Cucurbit aphid‐borne yellows virus (CABYV) transmitted by the cotton aphid Aphis gossypii were studied under semi‐field conditions. Aphids and natural enemies were released inside insect‐proof cages with a CABYV‐infected cucumber plant placed in the centre of the cage and surrounded by 48 healthy cucumber seedlings. The spatiotemporal dynamics of the virus and vector were evaluated in the short (7 days) and long term (14 days) in the presence and absence of each predator. The spatial analysis by distance indices methodology, together with other indices measuring the dispersal around a single focus, was used to assess the spatial pattern and the degree of association between the virus and vector. The presence of C. carnea larvae and A. bipunctata adults induced A. gossypii dispersal after 14 days but not after 7 days. The reduction of the initial aphid population established in the plant located in the centre of each cage was always higher for C. carnea than for A. bipunctata. There was some evidence that the natural enemies affected the spread of CABYV, though more so for C. carnea than for A. bipunctata. This study suggests an influence of both predators on the spread of the aphid, mainly in the long term, but only weak effect of predators in the spread of the viral disease was demonstrated.