Two Anthocoris bugs as predators of glasshouse aphids – voracity and prey preference

Voracity and prey preference were evaluated for adult females of the predatory bugs Anthocoris nemorum (L.) and Anthocoris nemoralis (Fabricius) (Heteroptera: Anthocoridae) preying upon five species of aphids (Homoptera: Aphididae), of which Myzus persicae Sulzer, Aulacorthum solani (Kaltenbach), Macrosiphum euphorbiae (Thomas), and Aphis gossypii Glover are common pests in Danish glasshouse crops. Aphis fabae Scopoli was included to determine the influence of food quality on the preference of the predators, since A. fabae has proved to be of poor nutritional value to Anthocoris spp. The experiments were carried out over 24 h in climate cabinets at 20 °C, 60–70% r.h., L18:D6. The aphids were offered in equal amounts in combinations of two species in instars of comparable size. Myzus persicae served as a reference species in all combinations. Both predators accepted all five species of aphids as prey. The numbers of aphids killed per 24 h period varied between 3.7 and 18.0 for A. nemorum and between 3.6 and 12.7 for A. nemoralis. Field collected A. nemorum females, presumably in a state of reproductive diapause, killed in three of four prey combinations significantly more aphids than did ovipositing A. nemoralis females which originated from a commercial rearing. When A. nemorum females had terminated their reproductive diapause and commenced oviposition, voracity increased approximately threefold. When prey preferences were evaluated as a total number of killed prey, no difference in preference was found between the two Anthocoris species. Both predatory bugs preferred M. persicae to the other species, the most accepted alternative prey were A. gossypii, A. fabae, A. solani, and M. euphorbiae, in descending order. However, evaluating preference by number of aphids consumed, A. nemoralis showed a more pronounced preference for M. persicae, especially when combined with A. fabae. In nearly every case, A. nemoralis rejected A. fabae as a food item after killing the aphid. Thus, A. nemoralis exhibited a more specific food choice than A. nemorum. By killing and consuming different aphid species found in glasshouse crops – particularly M. persicae– both A. nemorum and A. nemoralis showed preliminary qualities as agents for the biological control of aphids.     

Oviposition preference of Anthocoris nemorum and A. nemoralis for apple and pear

Anthocoris nemorum L. and Anthocoris nemoralis Fabricius (Heteroptera: Anthocoridae) are important predators of insect pests in pome fruit. Females insert their eggs in leaf tissue. The females’ choice of oviposition site is important for the subsequent distribution of nymphs on host plants. Oviposition preference for apple and pear leaves was tested in the laboratory in four experiments (experiments 1–4). In three experiments it was tested whether simulated insect damage to leaves (experiments 5 and 6) or the presence of prey (experiment 7) influenced oviposition preference. The effect of the presence of prey was only tested for A. nemorum on apple leaves. There was a highly significant anthocorid species × plant interaction for the number of eggs laid on apple and pear leaves. Anthocoris nemorum laid more eggs on apple than on pear leaves, while A. nemoralis preferred pear. Anthocoris nemorum's preference for apple increased over the 6‐week period in which experiments 1–4 were performed, from 66% to 91% eggs laid on apple leaves. No change over time in preference was found for A. nemoralis. Across experiments 1–4, the majority of A. nemorum eggs were laid near leaf margins, whereas eggs of A. nemoralis were more commonly found in the leaf centre, 5 mm or more from the margin, with a highly significant leaf region × species interaction. There was no significant difference in preference for leaf side between A. nemorum and A. nemoralis, but there was a highly significant plant × leaf side × experiment interaction. Thus, more eggs were laid on the ventral than on the dorsal side of pear leaves in experiment 4, while significantly more eggs were laid on the dorsal side of apple leaves in experiments 3 and 4. Choice tests between damaged and healthy leaves showed that A. nemorum laid significantly more eggs on the damaged leaves, while A. nemoralis preferred healthy leaves. Anthocoris nemorum showed a near‐significant preference for ovipositing on leaves with eggs of Operophtera brumata (Lepidoptera: Geometridae). The oviposition preferences found correspond to the natural distribution of these predators in apple and pear orchards. The preference of A. nemorum for leaf margins, and of A. nemoralis for the leaf centre as an oviposition site, supports earlier observations. A preference for leaf side for oviposition site has not been reported earlier. Preference for damaged leaves could help A. nemorum to locate prey in a field situation.     

Parasitism byEphedrus cerasicola [Hym.: Aphidiidae] developing in different stages ofMyzus persicae [Hom.: Aphididae]

The parasitoidEphedrus cerasicola Stary oviposited in the 4 nymphal instars and in newly moulted apterous adults ofMyzus persicae (Sulzer). Development and reproduction of unparasitized and parasitized aphids at 21°C were compared. Unparasitized aphids developed to adults in 6.5 days and started to reproduce after 7 days. Longevity varied between 7 and 42 days. Net reproductive rate (R₀) was 40.7. In contrast to older nymphs, aphids parasitized in the 1 st instar almost never reached the adult stage before mummification. Aphids parasitized in 2nd, 3rd and 4th instar and as newly moulted adults produced respectively 0.07 %, 2 %, 23 % and 32 % of offspring produced by unparasitized aphids. Corresponding reproductive periods were 1, 1.4, 3 and 4 days. Host age at parasitization had a slight effect on the parasitoid's developmental rate and had no effect on egg or pupal survival, or on the sex ratio of the emerging parasitoids.     

Biological control ofAphis pomi [Hom.: Aphididae] ofAphidoletes aphidimyza [Dip.: Cecidomyiidae]; a predator-prey model

Predation ofAphis pomi DeGeer [Hom.: Aphididae] byAphidoletes aphidimyza (Rondani) [Dipt.: Cecidomyiidae] was simulated in Michigan apple orchards using a computer and output validated against field data collected from sleeve cages enclosing aphid infested apple terminals. Lower and upper temperature thresholds for development were 2.9 and 35°C for nymphs ofA. pomi with a mean immature developmental period of 162.3 heat units. Median survivorship of adultA. pomi was 364.3 heat units with an average fecundity of 60.7 offspring per female.A. aphidimyza egg and larval lower threshold and developmental periods were 10.5 and 25.5, 8.1°C and 65.5 heat units, respectively. Larval functional response showed Type II behavior with a y-asymptote of 45 aphids killed per predator. Multiple generation model runs performed under different initial predator: prey densities indicated that current critical predator: prey ratios used in the field for control decisions may underestimate predator efficacy.      

The effect of fungus infection ofMetopolophium dirhodum [Hom.: Aphididae] on the oviposition behaviour of the aphid parasitoidAphidius rhopalosiphi [Hym.: Aphidiidae]

The oviposition behaviour of the hymenopterous parasitoidAphidius rhopalosiphi onMetopolophium dirhodum nymphs at successive stages of infection with the aphid-pathogenic fungusErynia neoaphidis was compared with that on uninfected nymphs. The frequency with which the parasitoid attempted to oviposit diminished in aphids inoculated with the fungus 3 days previously, that is within only 24 h of dying of the infection, but not in those infected only 1 or 2 days previously. The parasitoid did not attempt to oviposit in aphids killed by the fungus.      

Superparasitism and host discrimination byEphedrus cerasicola [Hym.: Aphidiidae], an aphidiid parasitoid ofMyzus persicae [Hom.: Aphididae]

Myzus persicae (Sulzer) at different densities (1 to 120 aphids) on a paprika plant in a 1.8 dm³ cage were exposed at 21°C to single females of the parasitoidEphedrus cerasicola Stary. Three different exposure periods were used: 1 hr, 6 hrs, 24 hrs. The aphids were dissected 6 days after parasitization. Superparasitism was measured as number of hosts superparasitized and number of parasitoid larvae per aphid. It attained a maximum around host density=5 and decreased with increasing host density and decreasing exposure time. Almost no superparasitism occurred during the 1st hour. A non-random larval distribution indicated thatE. cerasicola discriminates between unparasitized and parasitized aphids, but probably not between aphids with different numbers of parasitoid eggs. Larvae in superparasitized aphids developed slower than single larvae. The supernumerary larvae died during the 1st instar, probably killed by chemical means since no physical attacks between larvae have been observed.     

The effectiveness of Anthocoris nemorum and A. Confusus (Hemiptera: Anthocoridae) as predators of the sycamore aphid, Drepanosiphum platanoides. II. Searching behaviour and the incidence of predation in the field

Laboratory observations on the searching behaviour and efficiency of the anthocorids Anthocoris confusus and A. nemorum in capturing the sycamore aphid led to the suggestion that the anthocorids would be unable to survive on sycamore trees unless the population density of young aphids on the leaves exceeded a certain value. This value is 14 and 5 small aphids per 10 dm² of leaf, for A. confusus and A. nemorum respectively.Analysis of observations on the incidence of predation by anthocorids on the sycamore aphid confirms that the number of anthocorid nymphs appearing on sycamore in the spring is related to the number of young aphids present. However, it is the numbers of parasitized aphids and adult aphids present in June and July that determine the proportion of the anthocorid nymphs that become adult. Despite their ability to avoid capture, adult aphids are so abundant in some years that this more than compensates for the anthocorids' inefficiency in capturing them.The proportion of the sycamore aphid population killed by the anthocorids in the field decreases as the sycamore aphid increases in abundance.

---

Zuammenfassung Über das Suchverhalten und die Wirksamkeit der Anthocoriden Anthocoris confusus und A. nemorum bei der Erbeutung von Ahornblattläusen wurden Laborbeobachtungen durchgeführt. Kombination der Ergebnisse mit Befunden über die Nahrungsbedürfnisse der Anthocoriden (Russel, 1970) ermöglichten dann Schätzungen über die Populationsdichte der Blattläuse, die für die erfolgreiche Entwicklung der Anthocoriden erforderlich ist. Die benötigten Werte betragen für A. confusus 14 und für A. nemorum 5 kleine Blattläuse pro 10 dm² Blattfläche.Eine Analyse von Beobachtungen über das Auftreten der Erbeutung von Ahornläusen durch die Anthocoriden bestätigt, daß die Anzahl der im Frühjahr an Ahorn auftretenden Anthocoriden-Larven in Beziehung zur Anzahl der vorhandenen jungen Bláttläuse steht. Jedoch bestimmt die Anzahl der parasitierten sowie der erwachsenen Blattläuse, die im Juni und Juli vorhanden sind, den Anteil der Anthocoriden-Larven, der das Adultstadium erreicht. Trotz der Fähigkeit der Ahornläus, der Erbeutung zu entgehen, wird in manchen Jahren die schlechte Fähigkeit der Anthocoriden, sie zu erbeuten, durch die Häufigkeit der Blattläuse mehr als ausgeglichen.Das Verhältnis der von den Anthocoriden im Freiland getöteten Ahornläuse nimmt in dem Maße ab, wie die Häufigkeit der Ahornläuse zunimmt.

     

Interactions betweenAcyrthosiphon kondoi [Homoptera: Aphidoidea] andAphelinus asychis [Hymenoptera: Chalcidoidea] and other parasites and hosts

In laboratory trials to investigate the parasite/host spectra of certain aphid pests and hymenopterous parasites, the aphidAcyrthosiphon kondoi Shinji encapsulated the egg of the aphelinid parasiteAphelinus asychis Walker. The resultant brown, sclerotic capsule was formed within 24 h of exposure of the aphid to parasitization and as far as is known prevented the development of the parasite to the larval stage. The capsule remained throughout the life of the aphid, whose longevity and fecundity were apparently not seriously impaired. A small number ofAphelinus escaped encapsulation, especially in aphids already containing capsule(s), and developed into normal, reproductive adults.A. kondoi did not encapsulate, andA. asychis was not encapsulated by any other species. However, thoughA. asychis readily parasitizedAphis citricola van der Goot,A. nerii Boyer de Fonscolombe andToxoptera citricidus (Kirkaldy), most of its progeny ceased development in these aphids before reaching the mummification stage, and died within the dead or dying, non-mummified aphid host.     

The action of some systemic aphicides on the nymphs of Anthocoris nemorum (L.) and A. confusus Reut

The aphicides phorate, dimethoate and menazon were compared to elucidate the different pathways by which they can affect Anthocoris nymphs and their aphid prey.
When nymphs were caged in contact with deposits on bean leaves phorate and dimethoate had contact LC 50s of 20 and 3 μg/cm² respectively to Anthocoris nemorum and 46 and 6 μg/cm² to A. confusus. When the nymphs were confined on treated leaves on the opposite surface to the deposits, neither phorate nor dimethoate killed them. Menazon did not kill anthocorids at any dosage. All three aphicides killed over 50% of Acyrthosiphon pisum (Kalt.) on bean leaves at 1.6 μg/cm² whether the aphids were on the treated or untreated surface.
Experiments with ³⁵S-labelled phorate showed that anthocorids confined on phorate-treated bean plants, with or without insect food, accumulated the insecticide or its labelled derivatives. In field experiments in which A. nemorum were caged on plants treated with phorate, many were killed on young newly treated plants but not on older plants. A. confusus was relatively unaffected.
Anthocorids were reared from 2nd-instar nymphs to adults on aphids killed systemically with phorate, dimethoate or menazon without ill effects, despite evidence that ³⁵S-labelled phorate was ingested from the aphids and excreted in the faeces.
In the field, fewer large A. nemorum nymphs were found in August in plots of tick beans treated with phorate granules at 6 lb/acre (6.7 kg/ha) when sown, than in plots treated at 1.5 lb/acre (1.7 kg/ha) with phorate or menazon or untreated plots.     

Efficiency of four heteroptera as predators ofAphis gossypii andMacrosiphum euphorbiae (Hom.: Aphididae)

Predation rate and nymphal development time were determined for four predatory bugs (Dicyphus tamaninii Wagner andMacrolophus caliginosus Wagner [Het.:Miridae],Orius laevigatus (Fieber) andO. majusculus (Reuter) [Het.:Anthocoridae], on cucumber withAphis gossypii Glover (Hom.:APhididae) as prey and for both mirids also on tomato withMacrosiphum euphorbiae (Thomas) as prey. All four predator species were able to achieve adulthood feeding on both aphids. The developmental period ofD. tamaninii nymphs was the longest and the shortest was forO. majusculus. During nymphal developmentD. tamaninii consumed greater numbers of both aphids thanM. caliginosus, whileOrius’ consumption ofA. gossypii was intermediate. Average daily predation was higher forD. tamaninii than forM. caliginosus, but was not different from bothOrius species. FemaleD. tamaninii exhibited a typical type-II functional response when preying on varying densities ofA. gossypii nymphs.     

The action of some systemic aphicides on the eggs of Anthocoris nemorum (L.) and A. confusus Reut

Comparisons were made of the systemic action of phorate, menazon and dimethoate on Aphis fabae Scop, and on the eggs of the aphidophagous Anthocoridae Anthocoris nemorum (L.) and A. confusus Reut., which are laid within plant tissue. Against 4th-instar apterous A. fabae the order of toxicity of the insecticides taken up by roots of the field bean Vicia faba L. was: menazon > dimethoate > phorate. Phorate concentrations needed to kill all A. fabae (10–15 ppm of wet weight of plant) killed most A. nemorum eggs but did not harm A. confusus eggs. Few A. nemorum eggs were killed by 15 ppm of menazon or 5 ppm of dimethoate. In the field a commercial in-row treatment of 1·5 lb/acre of phorate applied as granules in the seed drill of field beans sown in late April killed 86 % of eggs laid in June by overwintered A. nemorum and 30% of those laid in late July by second-generation females. Plants initially treated with 6 lb of in-row phorate per acre killed 74% of A. nemorum eggs in late July but did not harm A. confusus eggs. A. nemorum eggs laid in early June were unharmed by 1·5 lb/acre of in-row menazon. Of the A. nemorum eggs, 92–96% were inserted into the stipules and leaf margins of young bean plants, i.e. in the region (peripheral and distal part of the leaf) where most ³²P from labelled phorate accumulates after root uptake. The egg-laying sites of A. nemorum in potatoes and brussels sprouts (edges of the leaves) and in oats (the leaf tips) are also where most of the ³²P accumulates. In contrast, 98% of A. confusus eggs were laid in the stems, petioles and leaf midribs of field beans, where there was generally much less ³²P from labelled phorate.     

Assessment ofPaulinia acuminata [Orthoptera: Acrididae] for the biological control ofSalvinia molesta in Australia

The biology and host specificity of the aquatic grasshopper,Paulinia acuminata (De Geer) were studied in quarantine in Australia. Adults and nymphs fed on the leaves of salvinia (Salvinia molesta), water lettuce (Pistia stratiotes) and azolla (Azolla pinnata). Fifty-three plant species representing 38 families were exposed to adults and nymphs ofP. acuminata. Adult feeding occurred on 17 plants but nymphs failed to feed on 9 of these species in the presence ofS. molesta. In starvation trials, 14 plants (excludingS. molesta, P. stratiotes andA. pinnata) were attacked by adults, of which only 5 were attacked by nymphs. Heavy feeding occurred on strawberry (Fragaria xananassa) but no oviposition occurred even when the leaves were held in contact with the water surface. The life cycle ofP. acuminata was completed only onS. molesta, P. stratiotes andA. pinnata. Eggs deposited on water hyacinth (Eichhornia crassipes) failed to hatch. Laboratory evaluation was supplemented with observations on the distribution and abundance ofP. acuminata on the Zambezi River system, Zimbabwe, during October 1984.     

Some interactions ofSerratia marcescens nucleopolyhedrosis virus andBlepharipa pratensis [Dip.: Tachinidae] inLymantria dispar [Lep.: Lymantriidae]

The entomopathogensSerratia marcescens Bizio and nucleopolyhedrosis virus were each fed alone and in combination with the parasiteBlepharipa pratensis (Meigen) to 4th-instar gypsy moth,Lymantria dispar, (L.) larvae. At LD₃₀ for NPV, the presence of the parasite enhanced polyhedrosis about 30%, but the total number of gypsy moth larvae and pupae killed (85%) was not significantly different from the number killed by the parasite alone (93%). When the parasite was combined withS. marcencens, a strain nonpathogenic inL. dispar, total mortality was not significantly different from that in insects exposed only to the parasite (89 and 86%, respectively), but parasite survival was reduced about 12%. However, deaths not attributable to the parasite could not be ascribed to the bacterium either.     

The natural prey of three species of Anthocoris (Heteroptera: Anthocoridae) living on broom (Sarothamnus scoparius L.)

The natural prey of A. nemorum, A. nemoralis and A. sarothamni were studied by means of the precipitin test. The results show that A. nemoralis and A. sarothamni feed predominantly on broom psyllids. A. nemorum does not appear to be so restricted in its prey.

---

Zusammenfassung Die natürliche Beute von Anthocoris nemorum, A. nemoralis und A. sarothamni wurde mit Hilfe des Präzipitintests untersucht. Dieser Test beruht auf der Reaktion von Beutesubstanz im Darm eines Räubers mit Antikörpern im Blutserum von Kaninchen, die mit einem Extrakt der Beute geimpft worden waren. Die Ergebnisse zeigen, daß A. nemoralis und A. sarothamni vorwiegend von Besenginster-Psylliden (Arytaina spartiophila und A. genistae) leben. Die Spezifität ihrer Beutewahl ist so ausgeprägt, daß die von diesen beiden Arten in jeder Generation erzeugte Anzahl von Larven eng an die Zahl der vorhandenen Blattflöhe gebunden ist. A. nemorum scheint bezüglich seiner Beute nicht so beschränkt zu sein und ist wahrscheinlich ein allgemeiner Prädator vieler kleiner Arthropoden. Dies stimmt mit seinem Auftreten an einem breiten Sortiment von Wirtspflanzen überein. Die Populationsdichte von A. nemorum scheint keiner seiner Beutearten zu folgen.

     

Mechanische und physiologische Abwehrreaktionen einiger Blattlausarten [Aphididae] gegen Schlupfwespen [Hymenoptera]

Summary It was known from earlier experiments thatRhopalomyzus ascalonicus (Donc.) encapsulated the eggs andRhopalosiphoninus staphyleae (Koch) ssp.tulipaellus Theob. the larvae ofAphelinus semiflavus How., but, on the other hand, the mechanical defence reactions of both aphids against the parasite appeared to be conspicuously weak. These experiments were now extended to the parasiteDiaeretiella rapae (M'Intosh) and to the aphidNeomyzus circumflexus (Buckt.). Also the eggs ofD. rapae were encapsulated byRh. ascalonicus without any exception. N. circumflexus only killed the larvae ofD. rapae andA. semiflavus by encapsulation, but some larvae of the second species remained alive. The defensive behaviour of this host during the approach and the attack byA. semiflavus was markedly less developped than that ofMyzus persicae (Sulz.) and was comparable to the behaviour of the two other aphid species. Probably, the defence behaviour of the investigated aphids was reduced when after phylogenetic development of the blood reaction it had become dispensable.      

Maternal death relaxes developmental inhibition in nymphal aphid defenders

In certain aphids, first-instar nymphs defend their gall by attacking intruding arthropod predators. One correlate of such defensive behaviour is a lengthened duration of the first nymphal stadium during the galling phase of the life cycle. A prolonged first stadium allows a large army of first-instar defenders to accumulate, which may be advantageous for gall defence. The factors determining developmental delay have been unclear, however. Our field experiment with Pemphigus obesinymphae, a North American gall-forming aphid with defensive first-instar nymphs, tests whether first-stadium duration is influenced by the death of the colony''s fundatrix (mother). We killed fundatrices in certain galls, left those in control galls alive, and counted aphids in each stadium in each gall. Galls in which fundatrices were killed contained a lower proportion of first-instar defenders and more late-instar nymphs than did galls with living fundatrices, indicating that maternal death dramatically increased developmental rate of nymphs. Possibly nymphal aphids respond adaptively to environmental cues that signal a threat to the colony''s welfare. Alternatively, the fundatrix actively suppresses offspring development in order to maintain a large army of soldiers to protect her gall. The results add a new layer of complexity to our understanding of social aphid systems.     

Parasites ofSpodoptera exigua,S. eridania [Lep.: Noctuidae] andHerpetogramma bipunctalis [Lep.: Pyralidae] collected fromAmaranthus hybridus in field corn

Three species of lepidopterous larvae were collected fromAmaranthus hybridus L. growing in field corn during 1975 and 1976 at Hastings, Florida.Spodoptera exigua (Hubner) was the predominant species in May.Spodoptera eridania (Cramer) was predominant in June andHerpetogramma bipunctalis (F.) in July and August. Nine native species of parasites, representing theBraconidae, Eulophidae, Ichneumonidae andTachinidae, emerged from these larvae.Meteorus autographae Muesebeck emerged from bothS. exigua andS. eridania. TheTachinidae, Winthemia rufopicta (Bigot),Eucelatori rubentis (Coquillett) andLespensia sp., emerged from mixtures ofS. exigua andS. eridania. Apanteles marginiventris (Cresson),Temelucha sp., andChelonus texanus Cresson emerged from bothS. exigua andH. bipunctalis larvae, andEuplectrus platyhypenae Howard andOphion sp. emerged fromS. eridania. All the species of parasites from the lepidopterous larvae that feed onAmaranthus hybridus are also reported as parasites ofS. frugiperda, a serious pest of corn. Therefore these larvae onA. hybridus may be a source of the parasites found attackingS. frugiperda.     

Biology ofclausicella suturata [Dipt.: Tachinidae] a parasite ofEctomyelois ceratoniae [Lep.: Phycitidae]

The tachinid flyClausicella suturata Rondani is a solitary parasite ofEctomyelois ceratoniae (Zeller). It was grown under laboratory conditions (26±0.5°C, 55±5% R.H.) and the host-parasite relationships were studied. The different stages of the parasite were briefly described. The eggs are deposited on the carob (Ceratonia siliqua L.,Caesalpiniaceae) pods, near the openings of the host's tunnels and hatch immediately. The Ist instar maggot is directed by the web fibers of the host towards the caterpillar which is hidden in the carob pod. The parasites develop normally only in 4th and 5th instar caterpillars. The parasitized caterpillar spins its cocoon inside the carob pod before being killed by the parasite. The fully grown maggot leaves the host and pupates inside its cocoon. Adult longevity is dependent upon the presence of carbohydrate in the diet. Maximal male and female longevity (50% survival of 21 and 17.5 days respectively) was reached on a carbohydrate diet and water, at 26°C and 55% R.H. Newly emerged females readily mate with one or two-day old males. The average fecundity of a female is 202 eggs, deposited during 13.6 days, after an incubation period of 6.9 days. Superparasitism is common in nature but only one maggot is successful in completing its development.     

Life history ofAphis gossypii on cucumber: influence of temperature, host plant and parasitism

Life table data forAphis gossypii Glover (Homoptera: Aphididae), an important pest in glasshouse cucumber crops, were studied at 20, 25 and 30°C on two cucumber cultivars (Cucumis sativus L.) in controlled climate cabinets. The development time on the cucumber cv. ‘Sporu’ ranged from 4.8 days at 20°C to 3.2 days at 30°C. Immature mortality was approximately 20% and did not differ between temperatures. Most mortality occurred during the first instar. Reproduction periods did not differ among temperatures, but at 25 and 30°C more nymphs were produced (65.9 and 69.8 nymphs/♀, respectively) than at 20°C (59,9 nymphs/♀) because of a higher daily reproduction. Intrinsic rate of increase was greatest at 25°C (r _m =0.556 day⁻¹). At 20 and 30°C the intrinsic rate of increase was 0.426 and 0.510, respectively. On cv. ‘Aramon’, the development time ofA. gossypii was approximately 20% longer at all temperatures. Immature mortality did not differ between the two cultivars. The intrinsic rate of increase on cv. ‘Aramon’ was 15% smaller than on cv. ‘Sporu’. The use of cucumber cultivars partially resistant to aphids is discussed in relation to biological control of cotton aphid in glasshouses. Development time and immature mortality on leaves of the middle and upper leaf layer of glasshouse grown cucumber plants (cv. ‘Aramon’) were comparable to development in the controlled climate cabinets. On the lower leaves immature mortality was much higher (approximately 82%) than on leaves of the middle (24.0%) and upper leaf layer (24.5%). Reproduction was less on the lower leaf layer (45.9, 70.5 and 70.1 nymphs/♀ on leaves of the lower, middle and upper leaf layer, respectively). Aphids, successfully parasitized byAphidius colemani Viereck (Hymenoptera: Braconidae) only reproduced when they were parasitized after the third instar. Fecundity was 0.1 to 0.9 and 10.5 to 13.3 nymphs/♀ for aphids parasitized in the fourth instar or as adults, respectively. Reproduction of aphids that were stung but survived the attack was lower than for aphids not stung. Average longevity of these aphids was equal to the longevity of aphids not stung byA. colemani.     

Interference between parasitoids [Hym.: Aphidiidae] and fungi [Entomophthorales] attacking cereal aphids

In field populations of cereal aphids parasitism levels declined through the season as fungal infection increased. In laboratory trials the fungusErynia neoaphidis Remaudiere & Hennebert took 3 to 4 days to kill the rose-grain aphid,Metopolophium dirhodum (Walker), whereas the parasitoidAphidius rhopalosiphi De Stefani-Perez took 8 to 9 days at 20°C. When aphids were infected by the fungus less than 4 days after being parasitized the parasitoids were prevented from completing their development. Conversely, when infection occurred more than 4 days after parasitization development of the fungus was significantly impaired. There was no histological evidence that the fungus invaded the tissues of the parasitoid when both attacked the same aphid. Interference between parasitoids and fungal pathogens must be taken into account when estimating the impact of these mortality agents on pest populations.