Parasitoid-host relationship betweenTrioxys (Binodoxys) Indicus [Hymenoptera: Aphidiidae] andAphis Craccivora [Hemiptera: Aphididae]. VI. Impact of males on the number of progeny of the parasitoid reared on certain host plants

The present paper elucidates the impact of males on the reproductive rate ofTrioxys (Binodoxys) indicus reared on the aphids ofCajanus cajan, Dolichos lablab andSolanum melongena host plants. The F₁ offspring increases with the increase of parasitoid number. This increase is maximum inC. cajan followed byD. lablab andS. melongena reared aphids. The presence of male parasitoids caused a significant decrease in the emergence of F₁ generation.      

Pale coloration in Aphis fabae reared on beans treated with the plant growth regulator,ethylene-bis-nitrourethane

Aphis fabae reared on broad bean plants treated with the experimental growth stimulator ethylene-bis-nitrourethane were extremely pale in colour and this persisted for the life of the individual, even when first instar nymphs were transferred from treated to untreated plants. Pale aphids had less than half the amounts of the pigments protoaphin and aphinin that were present in normal aphids. It is concluded that the aphids probably received a compound which inhibited pigment formation from the treated plants; the chelating properties of the metabolite of the compound in plants are consistent with this conclusion.     

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

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

Effects of brief exposures to low temperature on the development, longevity and fecundity of the grain aphid Sitobion auenae (Hemiptera: Aphididae)

First instar nymphs and adults of the grain aphid Sirobion auenae that had been reared at 10°C and 20°C over a number of generations, were cooled to -5°C and -10°C for 1 h and 6 h and returned to 20°C to assess the effects of brief exposures to low temperatures (cold-pulses) on their survival. rate of development, longevity and fecundity. A strong acclimation response was observed in first instar nymphs, with significantly less mortality in groups reared to 10°C compared to 20°C. Mean development time from first instar to adult was not significantly affected by low temperature exposure at the first nymphal stage. Longevity in all groups cooled as first instars was reduced by the sub-zero cold-pulses, and was also dependent on temperature and exposure time. Acclimated aphids survived longer than non-acclimated individuals. Reproductive rate, in terms of the number of nymphs born per aphid per day, was unaffected by cold stress applied at the first instar stage. Total fecundity was however reduced, being a function of the number and longevity of the survivors. Adult aphids were less cold hardy than nymphs; mortality was higher at -10°C than -5°C increasing with duration of exposure from 1 h to 6 h. Mean fecundity was reduced significantly in aphids cooled at the adult stage, the number of aphids born per day decreasing as the exposure period of the cold-pulse increased, suggesting that low temperature had affected embryogenesis. All the nymphs born to adults surviving exposure to -5°C for 6 h died within 48 h of birth, indicating that low temperature has a pre-natal effect on mortality.     

Suitability of greenbugs, cotton aphids, andHeliothis virescens eggs for development and reproduction ofOrius insidiosus

Development, fecundity, and longevity of the predator,Orius insidiosus (Say) (Heteroptera: Anthocoridae), when reared on greenbug [Schizaphis graminum (Rondani)], cotton aphid (Aphis gossypii Glover), or eggs of tobacco budworm [Heliothis virescens (F.)] with green beans or water were examined. Developmental time was shortest when predators were reared onH. virescens eggs and beans and longest when reared on cotton aphids and water. Predators were most fecund when fedH. virescens eggs. The inclusion of beans in the nymphal diet further enhanced fecundity when fed eggs. Longevity of both females and males was significantly shorter when reared on aphids than on eggs. Beans in the nymphal diet enhanced longevity of female predators only in combination with budworm eggs. FemaleO. insidiosus were largest when reared onH. virescens eggs. Addition of green beans in aphid treatments resulted in increased size ofO. insidiosus when compared to aphids and free water.     

Influence of plant,animal and mixed resources on development of the zoophytophagous plant bug Campylomma verbasci (Hemiptera: Miridae)

The mullein bug, Campylomma verbasci (Meyer-Dür) (Hemiptera: Miridae), exploits both plant and animal resources. The aim of this study was (1) to evaluate the quality of different plant, animal and mixed diets (i.e. plant material or prey from the overwintering host, the summer host or the laboratory rearing) for the development and survival of mullein bug, and (2) to evaluate if the suitability of the resource changes according to the nymphal instar of C. verbasci. Mullein bug nymphs were reared individually in Petri dishes containing different diets and observed daily until reaching adulthood or dying. The rearing diet (living potato aphids?+?potato leaf?+?Ephestia eggs?+?apple pollen) was a high-quality diet. The medium-quality diets were apple fruit?+?apple pollen, Ephestia eggs and Sitotroga eggs. The low-quality diets included mullein leaf, frozen aphids, living aphids?+?potato leaf and apple fruit?+?living aphids?+?potato leaf. Finally, the inappropriate diets (when no nymphs reached adulthood) were agar gel, apple fruit, apple pollen, apple leaf, potato leaf, frozen spider mites and frozen conspecifics. When comparing the value of the diets for different instars, living aphids?+?potato leaf was a high-quality diet for third instar. Apple pollen and frozen conspecifics were low-quality diets for third instar. ‘Red Delicious’ fruit was a high-quality diet for fifth instar and low-quality for third instar. ‘Honeycrisp’ fruit constituted an inappropriate diet whatever the instar. Thus, a whole mixed diet maximises development and survival of C. verbasci nymphs.     

Defense by a few first-instar nymphs in the closed gall ofdinipponaphis autumna (homoptera, aphididae, hormaphidinae)

The defensive behavior of the aphidDinipponaphis autumna, which forms small, completely closed galls on leaves ofDistylium racemosum, was observed. In mature galls, in addition to tens of mature or nearly mature aphids of the 3rd generation, there remained 3 – 17 1st-instar nymphs of the same generation, which had well-sclerotized legs and the antennae with developed setae. Despite their minority, these 1st-instar nymphs clung to experimentally introduced insect larvae and stung them with their stylets. Fourth-instar wingpadded nymphs, the majority of the 3rd generation at the experiment, also attacked the introduced larvae, but they were readily spilt from the larvae. Four out of 205 1st-instar nymphs remaining in mature galls had the next instar cuticle developing inside, indicating that they are not destined to be sterile.     

Alaboratory evaluation ofAnthocoris nemorum andA. nemoralis [Hem.: Anthocoridae] as predators ofPhorodon humuli [Hom.: Aphididae]

Anthocoris nemorum (L.) andA. nemoralis (F.) were reared on apterous hop aphids,Phorodon humuli (Schrank), at 20±0.5°C.A. nemorum andA. nemoralis killed an average of 255 and 174 aphids respectively during nymphal development, and the adults killed 37 and 33 per day respectively. Small anthocorid nymphs selectively killed small aphids but adult anthocorids and 5th instar nymphs killed aphids of every size. Mean development times from emergence to final moult were 22 and 16 days forA. nemorum andA. nemoralis respectively.     

Host plant influences pathogenicity of Beauveria bassiana to Bemisia tabaci and its sporulation on cadavers

Laboratory bioassays were conducted to determine host plant effect on pathogenicity of the entomopathogenic fungus Beauveria bassiana (Balsamo) Vuill. (Ascomycota: Hypocreales) to the sweetpotato whitefly, Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae). Fourth instar B. tabaci reared on cucumber, tomato, melon, green pepper, potato, eggplant, marrow, cabbage, bean or cotton, were treated with 1 × 10⁷ conidia/ml B. bassiana EABb 93/14-Tp isolate. Mortality caused by B. bassiana significantly increased with time and it was significantly affected by the host plant on which the nymphs were reared. Mean mortality of nymphs 8 days after inoculation ranged between 52.3±7.3 for nymphs reared on cotton and 91.8±5.8 for nymphs reared on cucumber. Average survival times of nymphs treated with the fungal suspensions were also significantly influenced by the host plant, with a mean of 4.7±0.1 days for nymphs reared on cucumber, 6.6±0.2 days for cotton and 6.9±0.1 days for green pepper. The production of newly formed conidia was also affected by host plant and varied from 111000±8600 conidia/cadaver for nymphs reared on cotton to 597000±28000 conidia/cadaver for those reared on melon.     

Resistance in cattle againstRhipicephalus appendiculatus with an assessment of cross-resistance toR. pulchellus (Acari: Ixodidae)

A comparison of the yield of engorged nymphs ofRhipicephalus appendiculatus andR. pulchellus was carried out between cattle highly resistant toR. appendiculatus but susceptible toR. pulchellus, and cattle and rabbits susceptible to both species.Resistant cattle yielded fewer and smallerR. appendiculatus nymphs than either susceptible cattle or rabbits. More nymphs of both tick species dropped from susceptible cattle but no differences were detected in the mean weight of engorgedR. pulchellus nymphs fed onR. appendiculatus-resistant and susceptible cattle, although resistant animals yielded more nymphs ofR. pulchellus than ofR. appendiculatus.An acute inflammatory reaction, accompanied by intense pruritus and grooming, was observed in the ears of the resistant cattle infested withR. appendiculatus, but no reaction was detected in the opposite ears whereR. pulchellus was feeding.The low cross-resistance between these two closely related tick species suggests that different antigens may be involved in the development of resistance in cattle to different tick species.     

Density-dependent physiological phase in a non-migratory grasshopperAiolopus thalassinus

Aiolopus thalassinus thalassinus (Fabricius) (Orthoptera: Acrididae) is a non-migratory grasshopper of widespread geographical distribution, also endemic in the Tel-Arad region of the Northern Negev of Israel, where it is liable to sporadically damage agricultural crops. Periodic sampling in uncultivated ‘batha’ and agricultural fields, conducted during 1990/1991, indicate thatA. thalassinus populations exhibit seasonal fluctuations in density. Local spatial and temporal distribution, within this region, are dependent on food availability. Field observations and laboratory studies suggest that the local population ofA. thalassinus exhibits genetic heterochromy unaffected by density. The duration of nymphal developmental is 34 days for nymphs reared in isolation, whereas crowded nymphs complete their development within only 21 days. No striking density related changes in gross morphometric features are evident, but, in adults from isolated culture, an increased abundance ofsensilla coeloconica, presumably involved in olfactory chemoreception, may be functionally related to enhanced (23.6-fold higher) activity of nymphs reared under crowded conditions. This higher level of activity is correlated to higher levels of energy reserves in the haemolymph — lipids and carbohydrates — and to increased respiration. Finally, the individual food consumption of nymphs from crowded culture is almost 5-fold higher than that of isolated nymphs and may increase the potential for crop damage. These results are similar to those obtained with the migratory locustLocusta migratoria and support the hypothesis that non-migratory grasshoppers exhibit some density-dependent physiological characteristics of locusts, but do not exhibit overt chromatic or morphometric phase characteristics.     

The effect of artificial diet on the production of alarm pheromone by Myzus persicae

The cornicle secretion of Myzus persicae reared on artificial diet only elicits an alarm response in plant‐reared conspecifics after the young aphids have been transferred to plants for 7 days. Acetate in the form of 0.32% sodium acetate has been added to the diet as an early step in synthesis of the alarm pheromone, (E)‐β‐farnesene (EBF). The cornicle secretion of diet‐reared aphids then elicits an alarm response. However, there is no difference in internal EBF concentration between plant‐ and diet‐reared aphids. Puncturing aphids, either plant‐ or diet‐reared, with a pin shows that both can elicit an alarm response, whereas it is reduced by half with diet‐reared individuals. Although there is no significant difference in the concentration of EBF produced, the total amount in diet‐reared aphids is increased by acetate in the diet to a level similar to that in plant‐reared individuals: the size of aphids reared on an acetate‐supplemented diet is increased and comparable with the size of those that are plant‐reared. Bioassays with a range of EBF concentrations show a high threshold for the alarm response. It is concluded that the different size of aphids reared on plants and standard diet results in them secreting, respectively, above and below the response threshold.     

Factors affecting the cold hardiness of the peach-potato aphid Myzus persicae

Supercooling point studies were used to investigate the factors influencing the cold hardiness of the peach-potato aphid Myzus persicae, a freezing-susceptible insect. Overwintering adults lost cold hardiness as winter progressed, with a variable proportion showing a marked reduction in supercooling ability. Cold hardiness increased in spring so that all individuals demonstrated extensive supercooling ability typical of aphids reared in the laboratory at 20°C with a long photoperiod; these levels of cold hardiness were maintained in the field during summer and early autumn. First instar nymphs demonstrated considerable cold hardiness all year. Surface moisture caused inoculative freezing in some first instar nymphs and adults when supercooled, but the majority were unaffected. In the laboratory, adults starved for 7 days at 5°C showed distinct losses of supercooling potential equivalent to those observed in the field during mid to late winter. No loss of cold hardiness was found in first instar nymphs starved under the same conditions. The results demonstrate that the cold hardiness characteristics of M. persicae are atypical of those observed in other freezing-susceptible insects and it is suggested that continued feeding during mild winter conditions allows maintenance of cold hardiness particularly in adult aphids, and provides a possible explanation for the successful anholocyclic overwintering of M. persicae during such winters.     

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.     

Seasonal changes in fat content,form, state of gonads and length of adult life in the sycamore aphid,Drepanosiphum platanoides (Schr.)

• 1 Even when reared under similar conditions of crowding and nutrition, first and second generation adult sycamore aphids differ in their morphology and physiology. Second generation adults have a smaller abdomen, a longer gut, greater fat reserves, less developed gonads, a longer reproductive diapause and live longer than first generation aphids.
• 2 Second generation nymphs reared in isolation develop into adults which have less well-developed gonads but a reproductive delay similar to that of first generation adults.
• 3 Crowding of second generation adults prolongs the reproductive diapause.

     

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.     

Previous infestation of pea aphids Acyrthosiphon pisum on broad bean plants resulted in the increased performance of conspecific nymphs on the plants

Abstract

We studied the effects of previous infestation of broad bean plants by pea aphids Acyrthosiphon pisum on the performance of conspecific nymphs on the plants and the involvement of jasmonic acid (JA)-related defenses. The time needed for newly emerged nymphs to become reproductive adults on broad bean plants previously infested by conspecifics (pre-infested plants) was significantly shorter than on uninfested (control) broad bean plants. The total numbers of nymphs produced by aphids on preinfested and control plants were not significantly different. Preinfested plants produced significantly less endogenous JA than that control plants did. To test the effect of JA decreases, we conducted experiments on the developmental duration of nymphs on broad bean plants treated with JA (JA-treated plants) before infestation. The time needed for nymphs to become reproductive adults on JA treated preinfested broad bean plants was not significantly different from that on JA-treated control plants. The results suggested a possible parental care by pea aphids: the adult aphids manipulated JA-related defenses in broad bean plants that had positive effects for their offspring.     

Effect of parasitism on flight behavior of the soybean aphid, Aphis glycines

Many aphid species possess wingless (apterous) and winged (alate) stages, both of which can harbor parasitoids at various developmental stages. Alates can either be parasitized directly or can bear parasitoids eggs or larvae resulting from prior parasitism of alatoid nymphs. Winged aphids bearing parasitoid eggs or young larvae eventually still engage in long-distance flights, thereby facilitating parasitoid dispersal. This may have a number of important implications for biological control of aphids by parasitoids. In this study, we determined the effect of parasitism by Aphelinus varipes (Hymenoptera: Aphelinidae) on wing development and flight of the soybean aphid, Aphis glycines (Hemiptera: Aphididae). We also quantified the influence of aphid flight distance on subsequent A. varipes development. Parasitism by A. varipes was allowed at different A. glycines developmental stages (i.e., alatoid 3rd and 4th-instar nymphs, alates) and subsequent aphid flight was measured using a computer-monitored flight mill. Only 35% of aphids parasitized as L3 alatoid nymphs produced normal winged adults compared to 100% of L4 alatoids. Flight performance of aphids parasitized as 4th-instar alatoid nymphs 24 or 48 h prior to testing was similar to that of un-parasitized alates of identical age, but declined sharply for alates that had been parasitized as 4th-instar alatoid nymphs 72 and 96 h prior to testing. Flight performance of aphids parasitized as alate adults for 24 h was not significantly different from un-parasitized alates of comparable ages. Flight distance did not affect parasitoid larval or pupal development times, or the percent mummification of parasitized aphids. Our results have implications for natural biological control of A. glycines in Asia and classical biological control of the soybean aphid in North America.     

Categories of resistance at different growth stages in halt,a winter wheat resistant to the Russian wheat aphid (Homoptera: Aphididae)

This study was designed to categorize the resistance to the Russian wheat aphid, Diuraphis noxia (Mordvilko), resistant hard red winter wheat, Halt, as compared with susceptible wheat, TAM 107, at four different growth stages. Antixenosis was expressed in Halt at growth stage Zadoks 30. Antibiosis in Halt affected fecundity, number of aphids produced per reproductive day, maximum number of nymphs produced in one day, and intrinsic rate of increase. Fecundity was lower on Halt than TAM 107, and more nymphs were produced on both varieties at growth stage 20 than 10 and 40. Fewer nymphs were produced per reproductive day and on maximum production days by aphids reared on Halt than by those reared on TAM 107. The intrinsic rate of increase of Russian wheat aphids reared on Halt was lower than aphids reared on TAM 107. Differences in plant height and plant dry weight did not occur. Chlorosis ratings showed greater damage at the earlier stages in Halt and TAM 107 and significantly more damage in TAM 107 than Halt at growth stages 10, 20, and 30. Leaf rolling occurred on infested plants of TAM 107 at growth stages 10, 20, and 30, but not growth stage 40. Halt plants did not exhibit leaf rolling. The presence of a significant level of tolerance could make Halt compatible with other integrated pest management programs. However, care should be taken with cultivars containing evidence of antixenosis or antibiosis that could cause selective pressure on the Russian wheat aphid, potentially causing biotypes to be produced.     

The overwintering and abundance of cereal aphids

The longevity of Sitobion avenae varied inversely with temperature from 25 to over 100 days when reared outdoors on barley under lantern jars, being longest between December and April–May. This was due mainly to changes in the length of the pre- and post-reproductive periods rather than the length of the period of reproduction. Fecundity varied directly with temperature, from eight to sixty-seven nymphs per female. When reared on winter wheat and sheltered from wind, rain and snow, S. avenae survived best, Metopolophium dirhodum survived less well and Rhopalosiphum padi worst; when exposed in the open none of the three species survived. Close relationships were not demonstrable between the numbers of alate M. dirhodum, S. avenae and Rhopalosiphum spp. trapped in any year, between the abundance of these aphids and weather conditions between January and April, or between the numbers of these alatae and the size of crop infestations. This was probably because insufficient information was available about their biology, both inside and outside the crop.