Recognition of heterospecific parasitism: Competition between Aphidiid (Aphidius ervi) and Aphelinid (Aphelinus asychis) parasitoids of Aphids (Hymenoptera: Aphidiidae; Aphelinidae)

The solitary parasitoids Aphidius erviHaliday (Hymenoptera: Aphidiidae) and Aphelinus asychisWalker (Hymenoptera: Aphelinidae) attacked but generally did not oviposit in pea aphids parasitized by the other species. Wasps selectively oviposited in unparasitized hosts when given a choice. Host discrimination depended on the recognition of internal cues. Females of A. asychiseither could not recognize or ignored A. ervi'sexternal host marking pheromone. Under most conditions, A. ervisurvived in superparasitized hosts, killing competing A. asychislarvae by physical attack and possibly physiological suppression. The outcome of larval competition was not affected by oviposition sequence or age difference between larvae; A. asychissurvived only when it had substantially completed larval development before the host was superparasitized by A. ervi.It is suggested that competition for host resources incurs a cost, for the winner in terms of reduced size or increased development time and for the loser in terms of lost progeny and searching time. Consequently, heterospecific host discrimination can be functional. Internal, and probably general, cues enable wasps to recognize and avoid oviposition in hosts already parasitized by an unrelated species.     

Functional responses of aphid parasitoids,Aphidius colemani (Hymenoptera: Braconidae) and Aphelinus asychis (Hymenoptera: Aphelinidae)

We evaluated the functional responses of two aphid parasitoids: Aphidius colemani on the green peach aphid Myzus persicae (Hemiptera: Aphididae), and Aphelinus asychis on M. persicae and the potato aphid, Macrosiphum euphorbiae (Hemiptera: Aphididae). Parasitoid oviposition occurred at host densities of 5, 10, 20, 30, 50, 80 or 100 aphids for A. colemani and 5, 10, 20, 30 or 50 aphids for A. asychis. More M. persicae were parasitized by A. colemani than by A. asychis at an aphid density of 50. Among the three types of functional response, type III best described the parasitoid response to the host densities both in A. colemani and A. asychis. The estimated handling time was shorter for A. colemani than for A. asychis (0.017 and 0.043 d, respectively). The proportion of aphids that were parasitized exhibited the same characteristic curve among the three host-parasitoid combinations: a wave form that appeared to be a composite of a decelerating (as in type II) response at low host density and an accelerating-and-decelerating (as in type III) response at medium to high host density. We hypothesize that the novel host species (and its host plant), density-dependent superparasitism, and/or density-dependent host-killing may have induced the modified type III response.     

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.     

Aphelinus albipodus(Hymenoptera: Aphelinidae) andDiaeretiella rapae(Hymenoptera: Braconidae) Parasitism onDiuraphis noxia(Homoptera: Aphididae) Infesting Barley Plants Differing in Plant Resistance to Aphids

Russian wheat aphid,Diuraphis noxia(Mordvilko), as a pest of small grains, has prompted research into biological control and host plant resistance. In the presence of Russian wheat aphid, leaves of a susceptible barley (Morex) are curled and chlorotic and sustain large densities of this aphid, while leaves of a resistant barley (STARS-9301B) remain flat and green and sustain fewer aphids. Might parasitism of Russian wheat aphid byAphelinus albipodusHayat & Fatima andDiaeretiella rapaeMcIntosh be affected differently by these plant types? When presented the plants separately and based on parasitism rate relative to aphid density, the largerD. rapaewas more effective in parasitizing relatively high densities of aphids within curled leaves of Morex than relatively low densities of aphids on uncurled leaves of STARS-9301B. Parasitism byA. albipodusdid not significantly differ among the plants. When given a choice of plants, approximately equal rates of parasitism occurred on the two plant lines for both parasitoid species, and parasitism byD. rapaewas greater thanA. albipodus.These data indicate that using parasitoid size as an indicator of success in a physically restricted environment may be misleading, when considered in a plant environment responsive in several manners to aphids (chlorosis, curling, and ability to sustain Russian wheat aphid). We expect that use of resistant barley will result in decreased parasitoid abundance as aphid densities decrease. However, parasitism rates are expected to be approximately equal on resistant and susceptible barley. In this system, plant resistance and biocontrol are compatible management strategies.     

Importance de la nutrition chezAphelinus sp. [Hym.Aphelinidae]

Résumé L'incidence de la nutrition sur la biologie des Aphélinides est étudiéc et analysée sous ses différents aspects: maturation sexuelle, spécificité parasitaire (adaptation à un nouvel h?te) et longévité. Les faits observés sont rapprochés de certains phénomènes d'adaptation à des facteurs du milieu connus chez d'autres groupes d'insectes. D'importants travaux ont été effectués sur un Aphélinide monophage,Aphelinus mali Haldeman depuis son introduction en Europe en 1929 pour freiner les pullulations du puceron lanigèreEriosoma lanigerum Hausm. Ce n'est que depuis une quinzaine d'années que les chercheurs américains ont orienté leurs recherches vers un autre Aphélinide,Aphelinus asychis Walker (=semiflavus Howard), susceptible d'attaquer un grand nombre d'espèces d'Aphides-h?tes. Cependant, la polyphagie de ce parasite fut très peu étudiée et c'est seulement en 1970 queRaney etal.,Manglitz & Schalk déterminant la fécondité du parasite en présence de divers h?tes, ont observé des différences de fécondité qui les ont conduits à considérer que certains h?tes étaient préférés par le parasite.

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Summary A study of polyphagous Aphelinids, parasites of aphids, revealed the existence of host conditioning. The physiology and behaviour of the female is influenced by the aphid species on which it feeds: sexual maturation, fecundity (measured by number of aphids mummified by one female) and longevity are impaired when this species differs from the one from which the female hatched. When females are fed with honey and water, longevity decreases (is reduced by about 15 days). Nutritive elements accumulated during larval life are used and eggs are progressively resorbed. This condition is not irreversible: if such females are reared with aphids, mature eggs can be observed after two days. Fecundity and longevity are decreased when one female (Aphelinus asychis), hatched from an aphid species A, is reared on an aphid species B. In the F₂ generation, the parasite is better adapted to the new host; in F₃ fecundity may be comparable with that recorded in females reared on aphid host A. However, if F₃ females hatched from species B mummies are now placed on aphid host A, the same kind of biological disturbances are observed as in the original transfer (A to B). After disproving the hypothesis of genetical selection of individuals adapted to the new host, the influence of nutrition on female physiology is demonstrated. This conditioning may be compared with that inAcrididae, attributable to a density factor, or that inNemeritis andDrosophila, to the odour of certain chemicals.

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Le présent article est extrait de la thèse de Doctorat d'état soutenue le 20 mars 1972 à l'Université Paris VI.     

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.      

Parasitoids of the gall-forming aphidSmynthurodes betae [Aphidoidea: Fordinae] in Israel

In an ecological investigation of the gall-forming aphid,Smynthurodes betae Westw., we discovered that more than 20% of the fundatrix galls were parasitized byMonoctonia pistaciaecola Stary (Aphidiidae). This is a new host record for this parasitoid. A Pteromalid hyper-parasite was identified asPachyneuron? leucopiscida Mani. Ecological information on the parasitoid is provided, and the low frequency of parasitoids known from gall-forming aphids, compared with freeliving ones, is discussed.     

Geographical distribution ofAphidiidae [Hym.] imported to California for biological control ofAcyrthosiphon kondoi andAcyrthosiphon pisum [Hom.: Aphididae]

A survey forAcyrthosiphon kondoi Shinji and its insect enemies was conducted in 1976–1977 in Afghanistan, Belgium, Czechoslovakia, Greece, Iran, Israel and Maroc. The search was concentrated in areas having cultivated species ofMedicago. A. kondoi was found only in Afghanistan, and in Iran. It was not found inMedicago-growing areas west from Iran, but it has been reported from India and Japan. Aphidius ervi Haliday,Aphidius urticae group,Praon barbatum Mackauer andAphidius smithi Sharma & Rao, were reared fromA. kondoi constituting new parasite records. New parasite and locality records were also found forA. urticae group,A. smithi andP. barbatum onAcyrthosiphum pisum (Harris). In laboratory trials, all cultures of parasitesA. ervi andP. barbatum readily parasitized and reproduced onA. kondoi onLens esculenta Moench. Cultures ofA. urticae group andA. smithi oviposited on, but did not complete development of immatures in,A. kondoi onL. esculenta. Hyperparasites identified as species includedAsaphes suspensus (Nees),Asaphes vulgaris Walker,Aphidencyrtus aphidivorus (Mayr),Dendrocerus breadalbimensis (Kieffer),Dendrocerus carpenteri (Curtis), andPachyneuron aphidis (Bouche). Available data suggest the origin of distribution ofA. kondoi may be Central Asia, and that populations ofA. ervi may be most suitable for colonization programs againstA. kondoi.     

Dynamic host-feeding and oviposition behavior of an aphid parasitoid <Emphasis Type="Italic">Aphelinus asychis</Emphasis>

In order to maximize the lifetime reproductive success of parasitoids, they should be induced to dynamically accept individual hosts that have different suitability for oviposition. Parasitoids tend to exhibit higher host-selective behavior when their egg load is limited, and are less selective if they are facing time constraints. Here, we evaluated the effects of parasitoid age on egg load, fecundity and host instar preference of a honey-fed aphid parasitoid, Aphelinus asychis Walker (Hymenoptera: Aphelinidae). Host selective experiment was conducted to measure host-preference of honey-fed A. asychis females at different ages, using the second and fourth instars of the green peach aphid Myzus persicae as their hosts. The results showed that the choice of host-instar for oviposition was significantly influenced by the parasitoid age. Honey-fed parasitoids in the age groups of 1, 5, 10 and 20 days tended to parasitize predominantly second-instar aphids, whereas 15-days old parasitoids showed no significant preference of host instars. On the other hand, host-feeding preference was not affected by parasitoid age. Parasitoid females of all ages preferred younger aphids to older aphids. This result could help evaluate the effectiveness of A. asychis for biological control of M. persicae when they encountered mixed-instar aphids in the field. In addition, the results might be helpful in assessing the host killing effects of other host-feeding parasitoids.     

Habitat preferences of aphidophagous coccinellids [Coleoptera]

From May to July 1982 and 1983, coccinellids were sampled in habitats that differed in aphid density, insolation, and host plant type. The number of adults ofCoccinella 7-punctata (CS),C. 5-punctata (CQ),Propylea 14-punctata (PQ),Adonia variegata (AV),Adalia bipunctata (AB),A. 10-punctata (AD), andCalvia 14-guttata (CA) were recorded. AB, AV and CS preferred high, while CQ tolerated low aphid density. CQ, CS, AB and AV preferred sunny, while AD and CA tolerated shaded conditions. CS and AV preferred herbaceous plants, AD and CA large plants, particularly trees, AB showed little specialization, CQ preferred trees early in the season and sparse herbaceous plants later. PQ appeared to be a generalist with a wide tolerance of all these factors, but with a tendency to move from trees to herbaceous plants as the season progressed. Habitats with a high abundance of a species were assumed to be those with on optimum combination of the preferred conditions. There were slight differences in the breadth of habitat preferences, and a little habitat overlap between species. The tendency to aggregate was greater in AB than in other species. Annual variations in species abundance influenced the number of habitats occupied, but not the abundance in the favoured places.     

Hexamermis glossinae [Nematoda: Mermithidae] parasitizing tsetse [Diptera: Glossinidae] in Kenya

Glossina pallidipes Austen,G. brevipalpis Newstead andG. austeni Newstead were collected from 5 sites along the south Kenyan coast over a 2 year period. They were dissected and examined for nematodes. Three of the sites yielded tsetse parasitized by juvenile mermithids identified asHexamermis glossinae Poinar et al. Glossina pallidipes andG. brevipalpis are new host records for this parasite, whileG. austeni was captured infrequently and only at a site that failed to yield other parasitized tsetse. Parasite prevalence was low (0.16–0.61 %) and did not differ between male and female hosts. More tsetse than expected by chance harboured nematodes during the long rains season (April–August) than during the short rains (September–November) or dry season (December–March). Early juvenile stages (0.5–2.5 mm long) were recovered mainly from tsetse less than 50 days old, while late juvenile stages (35–85 mm long) were only found in flies older than 30 days. Late stages occurred singly while early ones usually occurred as two or more per host.     

Fitness effects of two facultative endosymbiotic bacteria on the pea aphid,Acyrthosiphon pisum,and the blue alfalfa aphid,A. kondoi

The effects of two bacterial endosymbionts, designated PASS and PAR, were evaluated on the pea aphid, Acyrthosiphon pisum (Harris) (Hemiptera:Aphididae), in which they occur facultatively, and on the blue alfalfa aphid, A. kondoi Shinji, in which these bacteria have not been found in natural populations. Subclones of pea aphids and blue alfalfa aphids, derived from parent aphid clones that did not contain PASS or PAR, were infected with one or both bacteria, generating PASS- and/or PAR-positive subclones with minimal genetic differences from the parent clones. Under laboratory conditions at 20 °C, PAR consistently reduced the fecundity (by between 19 and 60%) of subclones derived from three different parent pea aphid clones on bur clover, Medicago hispida Gaertn. PAR had intermediate effects on pea aphids reared on sweet pea, Lathyrus odoratus L., and had no significant effect on pea aphids on alfalfa, Medicago sativa L. The effect of PASS was either neutral or negative, depending on parent clone as well as host plant. Also at 20 °C, PASS reduced fecundity (70–77%) and longevity (40–48%), and increased the age of first reproduction (by up to 1.5 days) of blue alfalfa aphid reared on alfalfa and clover. PAR had a less dramatic effect (e.g., 30–39% reduction in fecundity) on these traits of blue alfalfa aphid. In contrast, PAR and PASS increased the fitness of pea aphid subclones of one parent clone reared for three generations at 25 °C on each of the three test plants. Without facultative bacteria, fecundity of the parent clone was reduced to a mean total of < 6 offspring per adult at this elevated temperature, but with PASS or PAR, mean total fecundity of its subclones was > 35. However, this ameliorative effect of facultative bacteria at 25 °C was not found for two other sets of parent clones and their derived subclones. Alate production in pea aphids was significantly increased in large populations of two PASS- and PAR-positive subclones relative to their parent clones. Attempts to transmit PASS or PAR horizontally, i.e., from aphid to aphid via feeding on host plants (bur clover), were unsuccessful.     

The potential host ranges in Australia of some imported aphid parasites [Hym: Ichneumonoidea: Aphidiidae]

Host selection trials on restricted populations of the aphidiid parasites,Lysiphlebus fabarum (Marshall) andL. testaceipes (Cresson), imported into Australia as biological control agents ofAphis craccivora Koch, the cowpea aphid, have shown that these imported parasites are not widely polyphagous, and thus support a view that the 2 species, as presently recognized, each represent a complex of host-restricted biotypes or of sibling species. Whereas both of the importedLysiphlebus readily oviposited in species ofAphis andToxoptera, and developed successfully to adulthood inA. craccivora, A. gossypii Glover andT. aurantii (Boyer de Fonscolombe), they failed to complete development inA. citricola van der Goot, one of the most common aphid species in Australia, and only a small number completed development inT. citricidus (Kirkaldy). Both of these hosts, then, act as “egg traps” for theLysiphlebus. A. nerii Boyer de Fonscolombe was a suitable host forL. testaceipes but not forL. fabarum. NeitherL. fabarum notL. testaceipes oviposited inCavariella aegopodii (Scopoli),Brevicoryne brassicae (L.),Brachycaudus helichrysi (Kaltenbach),B. persicae (Passerini),Hyperomyzus lactucae (L.),Acyrthosiphon kondoi Shinji,A. pisum (Harris),Macrosiphum euphorbiae (Thomas) orM. rosae (L.); andL. fabarum did not oviposit inRhopalosiphum padi (L.) orMyzus persicae (Sulzer). The prognosis for the effective establishment in Australia of these 2 parasites is therefore not good In contrast, another purportedly polyphagous aphidiid,Praon volucre (Haliday), imported into Australia to help effect control ofH. lactucae, the sowthistle aphid, successfully and effectively parasitizedMacrosiphum euphorbiae, M. rosae, Acyrthosiphon pisum, A. kondoi, Aulacorthum solani (Kaltenbach),Myzus persicae andAphis craccivora, in addition toH. lactucae.     

Survey of the parasitoids of the tuliptree aphid,Illinoia liriodendri (Hom: Aphididae), in northern California

A survey of the parasitoids ofIllinoia liriodendri (Monell) in northern California conducted from 1988–1990 revealed the presence of 12 primary and 14 hyper-parasitoid species. The most common primary parasitoid wasAphidius polygonaphis (Fitch), which was imported from the eastern United States in the 1970's and is now established throughout the area. New host records were noted forA. ervi Haliday,A. avenaphis (Fitch), Praon occidentale Baker,P. unicum Smith,Diaeretiella rapae M'Intosh,Lysiphlebus testaceipes (Cresson), andMonoctonus nervosus (Haliday) (all Hymenoptera: Braconidae: Aphidiinae), andAphelinus sp. nr.asychis Walker (Hymenoptera: Aphelinidae). The most common hyperparasitoid species werePachyneuron aphidis (Bouché) andAsaphes californicus Girault (both Hymenoptera: Pteromalidae). New hyperparasitoid host records were noted forPachyneuron californicum Girault on Aphidiine and Aphelinidae spp. andCoruna clavata Walker (Hymenoptera: Pteromalidae) onAphelinus sp.     

Intraguild predation on the aphid parasitoid <Emphasis Type="Italic">Aphelinus asychis</Emphasis> by the ladybird <Emphasis Type="Italic">Harmonia axyridis</Emphasis>

We investigated intraguild predation (IGP) on an aphid parasitoid, Aphelinus asychis Walker (Hymenoptera: Aphelinidae), by the multicolored Asian ladybird, Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae), and used the green peach aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae) as the prey/host in the laboratory. The ladybirds reared on artificial diet and on aphids consumed more aphids than mummies, while those reared on parasitized aphids consumed similar numbers of aphids and mummies. The ladybirds chose more mummies in treatments when mummies were more abundant, and more aphids when numbers of aphids and mummies were equal, or when aphids were more abundant. However, at all density treatments, rejection rates of mummies (36%) were much greater than of aphids (2%). H. axyridis prey on more aphids than A. asychis mummies, which enhances biological control by the two species. However, prior feeding experience affected subsequent choice, increasing the competition between natural enemies which would reduce their combined effectiveness for biological control.     

Survival, growth, and reproduction of two aphid species on sucrose solutions containing host or non-host honeydews

Aphids, like most phloem-feeding insects, commonly exhibit a high degree of host specificity. Plant-specific chemical compounds are likely to serve as important host selection cues for monophagous aphids and such substances could be present in aphid honeydew. Apterous virginoparae ofMyzus persicae (Sulzer) andPhorodon humuli (Schrank) were reared on a buffered sucrose solution containing various aphid honeydews or a mixture of amino acids. In two separate experiments, the host-specificP. humuli (hop aphid) could grow and reproduce only on diets containing honeydew collected from hop (Humulus lupulus L.).M. persicae (the green peach aphid, GPA) did not perform well on diets containing hop honeydew, perhaps because hop is a poor GPA host. Honeydew collected from preferred GPA host plants rape,Brassica napus L., and jimsonweed,Datura stramonium L., allowed GPA growth and reproduction. Hop aphids, however, performed poorly on rape and jimsonweed honeydew diets. Bell pepper,Capsicum annuum L., honeydew supported neither the hop aphid nor GPA. The study of aphid honeydew components may contribute towards a more complete understanding of host preference and selection phenomena in aphids.     

Biological studies withChrysocharis parksi [Hym.: Eulophidae] a parasite ofLiriomyza spp. [Dipt.: Agromyzidae]

Biological studies withChrysocharis parksi Crawford, a parasite of agromyzid leafminers, were conducted.C. parksi successfully parasitized the following species in the genusLiriomyza Mik.,L. huidobrensis (Blanchard),L. sativae Blanchard,L. trifolii (Burgess), andL. trifoliearum Spencer. Successful parasite development was recorded from 8 plant families and 16 genera. Host plants which were suitable for leafminer development to the adult stage were also suitable for parasite development. Mean immature developmental period (egg to adult, usingL. trifolii as the host) at 21.1°, 26.7°, and 32.2° C was (for both sexes) 23, 14, and 14 days, respectively. Longevity of females provided only water was inversely related to temperature; significantly longer survival occurred at 21.1° C (5.0 days) compared to 26.7° C and 32.2° C (3.2 and 2.1 days, respectively). The addition of honey to the diet significantly improved longevity of both sexes at all temperatures. Adult female parasites which were provided an average of 33.0L. trifolii larvae per day produced an average of 135 offspring at a constant 26.7° C.C. parksi host-fed on ca. 3.7 leafminer larvae per day over an 11-day adult lifespan.      

Oviposition behaviour ofEphedrus cerasicola [Hym.: Aphidiidae] parasitizing different instars of its aphid host

The parasitoidEphedrus cerasicola Starý oviposited in all 4 nymphal instars and in newly moulted adults ofMyzus persicae (Sulzer). The different host categories were offered with no choice. The duration of an oviposition increased with the age of nymphs, being about 13, 18, 21, 22, and 17 s from 1 st instars to adults, respectively. Observations of number of stabbing attacks prior to oviposition, percent of the encounters not resulting in oviposition, time from first encounter to oviposition, handling time and aphid defensive behaviour also indicated that 1 st instarM. persicae are most easily parasitized. The behaviour ofE. cerasicola in encounters with unparasitized and parasitized hosts, suggested that the parasitoid could discriminate. In encounters with parasitized 1 st to 4th instar aphids,E. cerasicola used only the antennae in 80% of the encounters that resulted in discrimination.     

The biology ofAphelinus flavus [Hym. Aphelinidae], a parasite of the Sycamore aphidDrepanosiphum platanoides [Hemipt. Aphididae]

Aphelinus flavus Thompson is a solitary internal parasite. Males and females overwinter as free living adults and appear on sycamore in mid, May. The female consumes aphid body fluids and kills 1 aphid for food for every 1.7 eggs deposited, and parasitises 48 aphids over 27 days. Development from egg to adult requires and parasitises 48 aphids over 27 days. Development from egg to adult requires 57 days. The mortality of parasites while within the nummified host was determined: it was related to hyperparasitism and predation. Mortality due to mummies being brushed off the leaves was also determined.     

Aleurocanthus woglumi [Hom.: Aleyrodidae] andEncarsia opulenta [Hym.: Encyrtidae]: Density-dependent relationship between adult parasite aggregation and mortality of the host

Field and laboratory choice tests in which searching adultEncarsia opulenta Silvestri were exposed to variable densities of citrus blackfly,Aleurocanthus woglumi Ashby, indicated the following: (1) a direct functional relationship between adult parasite aggregation and host density, resulting in (2) a direct density-dependent mortality ofA. woglumi within a single generation timespan. The implications of such nonrandom searching patterns byE. opulenta on stability of the host-parasite interaction on Texas citrus are discussed.