Predators of citrus blackfly [Hom.: Aleyrodidae]

A 2-year survey of known whitefly predators was conducted from winter 1976 to winter 1978 in Broward County, Florida. Also, the impact of predators on citrus blackfly populations was measured under field conditions using lifetable data and predator exclusion data. In addition, feeding experiments were conducted to determine specific predators on different citrus blackfly stages. In the survey, the total number of predators caught in 1977 was significantly greater than 1978 and reasons for this difference are discussed. Spiders and the coccinellid,Delphastes pusillus Lec. were the most abundant predators being ca. 90% of all predators caught. Results from the lifetable and predator exclusion technique were similar showing that predators caused a 52 to 66% reduction in citrus blackfly populations. Feeding tests showed that predator responses to feeding on citrus blackfly were variable depending on species of predator, stage of predator, and stage of citrus blackfly.

---

Résumé Une étude pendant 2 ans des prédateurs de l'aleurode des citrus a été réalisée de l'hiver 1976 à l'hiver 1978 dans le Comté de Broward en Floride. L'influence des prédateurs sur les populations d'aleurodes a été mesurée dans les conditions naturelles par l'élaboration d'une table de vie et par des essais d'exclusion des prédateurs. En outre des expériences ont été effectuées afin de déterminer les prédateurs spécifiques pour chacun des stades de l'aleurode. Le nombre total de prédateurs capturés en 1977 fut significativement plus élevé qu'en 1978; les causes de cette différence sont discutées. Des araignées et la coccinelleDelphastes pusillus Lec. ont été les plus abondants, représentant et iron 90% du total. Les résultats de la table de vie et de l'exclusion des prédateurs ont été analogues et montrent que ceux-ci provoquent une réduction de 52 à 66% des populations d'aleurodes. Les essais sur l'alimentation indiquent que les réponses ont été variables selon l'espèce de prédateur, le stade du prédateur et de l'aleurode.

---

---

Florida Agricultural Experiment Station Journal Series No. 1791. Partly supported by funds from Cooperative Agreement # 12-14-7001-1148 between U.S.D.A., and University of Florida.     

Searching and ovipositional behavior ofAmitus hesperidum [Hym.: Platygasteridae] andEncarsia opulenta [Hym.: Aphelinidae] parasitoids of the citrus blackfly [Hom.: Aleyrodidae]

Searching behavior ofAmitus hesperidum Silvestri andEncarsia opulenta (Silvestri) for immatureAleurocanthus woglumi Ashby was similar. Both parasitoids moved unidirectionally until they encountered a host aggregation at which time they changed to a pattern of short walks with numerous turns. Parasitoid ovipositor insertion was generally at midbody between the host sternites and tergites.Amitus hesperidum females showed a significant preference for 1st instar hosts, have an ovipositional marker, do not feed on exudates from ovipositional wounds (host feed), and have significantly shorter ovipositional times and adult life spans thanE. opulenta which showed a significant preference for 2nd instar hosts, lack an ovipositional marker, and host feed.Encarsia opulenta females showed a significant preference for hosts previously parasitized byA. hesperidum but the reverse was not true. The average number of hosts parasitized by females of both parasitoid species was uninfluenced by the previous presence of the other parasitoid species on the same leaf.     

Lethal temperatures of citrus blackflyAleurocanthus woglumi [Hom.: Aleyrodidae] and its parasite,Amitus hesperidum [Hym.: Platygasteridae]

Seasonally acclimatized citrus blackfly (CBF),Aleurocanthus woglumi Ashby, and its parasite,Amitus hesperidum Silv. were exposed to extreme temperatures for 3-hour periods and survivorship measured. In summer experiments, the LD₅₀ for CBF adults and 1st instar nymphs occurred between 40° and 45°C. The LD₅₀ forA. hesperidum adults occurred between 35° and 40°C and increased with decreased humidity, although some adults could continue to emerge from parasitized CBF up to 45°C. In winter experiments, the LD₅₀ for CBF eggs and adults occurred between ?5° and ?10°C and for other CBF stages between ?10° and ?15°C. The LD₅₀ for adultA. hesperidum, and survival and emergence of the parasites from CBF both occurred between ?10° and ?15°C. Comparing data from the 2 seasons shows that adults are the most temperature sensitive stage of CBF and the parasite is more temperature sensitive than CBF, especially at higher temperatures. Correlating lethal temperature data with field meteorological conditions shows that short-term temperature exposures cannot be expected to stop the potential spread of CBF orA. hesperidum through Florida.     

A new species ofEncarsia [Hym.: Aphelinidae] parasitizingBemisia tabaci[Hom.: Aleyrodidae]

Encarsia deserti n.sp., a parasite ofBemisia tabaci Gennadius is described. It resemblesE. formosa Gahan, but has a light brown head and thorax, is smaller, and is biparental. This species was found in Southern California and Arizona parasitizingB. tabaci and was introduced into Israel for the control of this pest.     

Parasrnzatlon of bemisia argentifolii (Hom.: Aleyrodidae) by encarsia pergandiella (Hym.: Apheunidae)

The biology of the arrhenotokous autoparasitoid,Encarsia pergandiella Howard, was studied in the laboratory on the silverleaf whitefly,Bemisia argentifolii Bellows & Perring. Egg to adult development of parasitoid females averaged ca. 14 days at about 25.3+0.2?C regardless of whether the whitefly host was reared on tomato, eggplant or squash. While all instars ofB. argentifolii were accepted for primary parasitization, a greater percentage of third and fourth instars were parasitized. Mortality of whitefly nymphs in the absence of parasitization did not differ among instars and averaged about 35%. Second instar to pupal parasitoid females were accepted for secondary parasitization although a greater percent of pupal females were parasitized. About 40% of immatureE. pergandiella females more than 4 days old died in the absence of secondary parasitization when exposed to adultE. pergandiella females.     

Eretmocerus Corni Hald. [Hym. Aphelinidae] Parassita delSiphoninus Phillyreae Halid. [Hom. Aleyrodidae]

Summary A serious attack onPirus and some ornamentalRosaceae by the white flySiphoninus phillyreae Halid. was recently recorded in the province of Thessaloniki. About 20 per cent of the white fly population was parasitized byEretmocerus corni Hald. Described from America, the Aphelinid, was not found in Europe up till now.      

Biological control ofEucallipterus tiliae [Hom.: Aphididae] in san Jose,Calif., through establishment ofTrioxys curvicaudus [Hym.: Aphidiidae]

Trioxys curvicaudus Mackauer, an introduced parasitoid which had already proven successful in bringing the linden aphid,Eucallipterus tiliae L., under biological control in Berkeley, Calif., was released in 1978 in San Jose, Calif., where the aphid was still a pest. Recovery of the parasitoid was made later the same season. Monitoring and dissection studies ofE. tiliae in 1979 and 1980 demonstrated thatT. curvicaudus had become established in San Jose and was exerting a controlling influence on the aphid. Native natural enemies did not appear to have any appreciable effect on aphid numbers. It is proposed that prior to the introduction ofT. curvicaudus, the aphid's major limiting factor was the occurrence of mean daily temperatures above 22°C.

---

Résumé Trioxys curvicaudus Mackauer, parasitoide introduit qui a déjà fait ses preuves dans la lutte contre le puceron du tilleulEucallipterus tiliae L. à Berkeley en Californie, a été relaché en 1978 à San José (Californie), où ce même aphide constituait un problème en zones urbaine et suburbaine. Le parasitoide a été recapturé dès la fin de la même saison et jusqu'en 1980, terme de cette étude. Une surveillance régulière et des dissections deE. tiliae en 1979 et 1980 ont démontré queT. curvicaudus s'est établi à San José et exerce une influence dans la lutte contre ce puceron. Les ennemis naturels indigènes ne semblaient pas avoir un effet appréciable sur la densité de population deE. tiliae. Il est probable qu'avant l'introduction deT. curvicaudus, l'action des températures moyennes journalières supérieures à 22°C constituait le facteur essentiel limitant les populations de ce puceron.

     

Parasitoids attackingBemisia tabaci [Hom.: Aleyrodidae] in Eastern Africa

BioControl - Parasitoids ofBemisia tabaci were collected in Kenya, Malawi and Zimbabwe. The 2 principal species encountered wereEretmocerus mundus andEncarsia sublutea. Rates of parasitism varied,...     

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.     

Sustained biological control of the cassava mealybugPhenacoccus manihoti [Hom.: Pseudococcidae] byEpidinocarsis lopezi [Hym.: Encyrtidae] in Nigeria

Following the successful introduction ofEpidinocarsis lopezi (De Santis) for biological control of the cassava mealybug (CM)Phenacoccus manihoti Mat.-Ferr. in southwestern Nigeria in 1981 and 1982, 11 groups of cassava fields were sampled every 2 weeks up to 1988 for impact assessment. After 1984, CM populations remained mostly below 10 per tip despite the presence of native hyperparasitoids, demonstrating the long-term success of biological control byE. lopezi in the region. Indigenous polyphagous coccinellids were found only during peak host densities, whereas the specificE. lopezi was common throughout the year. During some periods, percentage parasitism indicated delayed density dependence. Since 89% of all sampled cassava tips had no CM at all and the parasitisme is very mobile, parasitization rates were also calculated for individual infested tips (N=4,878). Parasitism increased slightly with host density on tips having between 1 and 10 CM of the 3^rd and 4^th instars, indicating positive density dependence. Such tips comprised 64% of all infested tips. At higher host densities, parasitism rates fell rapidly. The results are discussed in view of different theories on population regulation by biological control agents.      

Establishment of the imported parasiteProspaltella perniciosi [Hym.: Aphelinidae] onQuadraspidiotus perniciosus [Hom.: Diaspididae] in Greece

Prospaltella perniciosi Tower was imported in Greece to aid in the biological control ofQuadraspidiotus perniciosus Comstock. Two to 10 years following release in apple trees the parasite was found well established onQ. perniciosus with low parasitism exceed to 2–5%. Parasitism by indigenous natural enemies, mostlyAphytis spp., was also low. Considering that these trees also suffer damage by other major pests, in order to obtain full benefit from the biological control ofQ. perniciosus compatible methods of supressing these pests are required.

---

Résumé Prospaltella perniciosi Tower fut importé en Grèce pour la lutte biologique contreQuadraspidiotus perniciosus Comstock. Deux à 10 ans après son lacher dans des vergers de pommier, le parasite est trouvé bien implanté dans la population de Pou de San José, le taux de parasitisme oscillant entre 2 et 5%. Le parasitisme par des ennemis naturels indigènes, principalement parAphytis spp., était aussi bas. Tenant compte du fait que ces arbres subissent des dégats par d'autres ennemis importants et afin d'obtenir le maximum d'efficacité de la lutte biologique contreQ. perniciosus, des méthodes adéquates pour la répression de cet insecte sont exigées.

     

The parasitoid complex [Hym.: Ichneumonoidea] ofToxoptera aurantii [Hom.: Aphidoidea] in the Mediterranean area

The parasitoid complex of the Black Citrus Aphid,Toxoptera aurantii (B.d.F.) in the Mediterranean area has been complemented on the basis of samples collected in South Italy and Lebanon. To the complex presently belong 10 Ichneumonoid species of the generaAphidius Nees,Diaeretiella Staryý,Ephedrus Haliday,Lipolexis Förster,Lysiphlebus Förster,Praon Haliday andTrioxys Haliday. Of these,Aphidius colemani Viereck, in spite of its wide distribution in the Mediterranean region, seems to be restricted to Near East (Israel and Lebanon) asT. aurantii parasitoid. The nearctic speicesLysiphlebus testaceipes (Cresson) is localized in Spain, South France, Corsica, Central and South Italy, including Sicily. In Italy, this endoparasitoid has heavily interfered with the local dominant congeneric speciesLysiphlebus confusus Tremblay & Eady andLysiphlebus fabarum (Marshall). The possible associative relationships betweenLysiphlebus testaceipes andL. fabarum have been examined in the samples collected in South Italy. The results of the examination suggest that the 2 species are negatively associated with each other, i.e. the abundance of 1 of the 2 species makes it more likely that the other will decrease in numbers. Moreover, the data concerning the relative abundance of both species in the same area indicate that a shift may have occurred in favour ofL. testaceipes between 1977 and 1978. The nearctic parasitoid seems to be able to displace the 2 congeneric species by a competitive biological mechanism which is still in course of investigation.     

Greenbugs [Hom.: Aphididae] forced from host plants byLysiphlebus Testaceipes [Hym.; Braconidae]

In a laboratory study 150 sorghum plants were infested with greenbugs,Schizaphis graminum (Rondani), of ages 1, 3, and 5 days in densities of 5, 10, and 20 aphids per plant. Seventy-five of these infested plants were exposed to mated femaleLysiphlebus testaceipes (Cresson), and the number of aphids leaving each plant in a 4-hr period was recorded. Of the 75 plants exposed to parasitoids, an average of 41.0% of the aphids left the plants, compared to 0.9% from the 75 control plants. Twenty-six of the 75 parasitoids used in the experiment were inactive in the presence of aphids, showing no interest in searching for hosts. The number of inactive parasitoids was inversely related to the number of aphids per plant. When only those plants exposed to active parasitoids were considered, an average of 62.8% of the aphids left. To determine the fate of greenbugs leaving plants on hot, sunny, summer days, a small field test was performed in which greenbugs were knocked from plants onto soil exposed to direct sunlight. Air temperature was ca. 29°C and soil temperatures ranged from 45°C to 54°C. Twenty-four greenbugs were knocked to the soil, and all of them ceased activity within 10 seconds and were apparently dead.     

Biological control ofAleurocanthus woglumi [Homoptera: Aleyrodidae] in El Salvador

The citrus blackfly,Aleurocanthus woglumi Ash., was first observed in El Salvador in 1965. Its dispersal was followed during a three-year period (1969–1972) in which it infested most citrus orchards in the country. Indigenous natural enemies as the predatorsDelphastus sp. andChrysopa sp., and the pathogenic fungusAschersonia aleyrodis Web. are unable to exert any economic control of the pest. The introduction of the parasiteProspaltella opulenta Silvestri from Mexico brought about the successful biological control of the pest. Life table studies carried out before and after introduction of the parasite helped to assess the value ofP. opulenta as an effective natural enemy of the citrus blackfly.

---

Résumé L'Aleurode des citrus,Aleurocanthus woglumi Ash. a été observé pour la première fois en Salvador en 1965. Son extension a été suivie pendant trois ans de 1969 à 1972, au cours desquels il a envahi la plupart des vergers d'agrumes du pays. Les ennemis naturels indigènes, tels que les prédateursDelphastus sp. etChrysopa sp. ainsi que le champignon pathogèneAschersonia aleyrodis Web. ne sont pas capables d'avoir un effet économiquement satisfaisant. L'introduction du Mexique du parasiteProspaltella opulenta Silvestri a été un succès pour la lutte biologique contre ce ravageur. L'étude des tables de vie effectuée avant et après cette introduction confirme la valeur deP. opulenta comme ennemi naturel officace de l'Aleurode des citrus.

     

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.     

Synchrony and impact ofAmitus hesperidum [Hym.: Platygasteridae] on its host,Aleurocanthus woglumi [Hym.: Aleyrodidae] in southern Florida

The synchrony of the citrus blackfly (CBF)Aleurocanthus woglumi Ashby and its parasitoidAmitus hesperidum Silvestri was studied in southern Florida.A. hesperidum adults emerge from 4th instar nymphs 160–300 thermal units after CBF adults. This insured excellent temporal synchronization between the parasitoids and the early CBF instars they prefer since egg to 3rd instar nymph in CBF takes 380 thermal units. AlthoughA. hesperidum parasitized only 29% of the surviving 4th instar CBF, it was the factor responsible for the observed decline in the CBF population level in southern Florida.     

Stability in the host-parasitoid relationship of Dialeurodes citri and Encarsia lahorensis in the citrus orchard

The citrus whitefly, Dialeurodes citri (Ashmead), a citrus pest, has been prevalent in Israel since 1975. The parasitic wasp Encarsia lahorensis (Howard) has been successfully used for its biological control since 1980 and thehost-parasitoid system is stable. This studyuses field data from four and a half years inorder to examine whether heterogeneity ofparasitism and risk aggregation can explain thestability. After establishing that theprobability of parasitism is not constant overpatches, we examined the question of parasitoidaggregation, dependent or independent of thehost, at different patch levels. At the treelevel we found an inverse relationship betweenthe proportion of parasitism and host density.At the leaf level, taking the tree effect intoconsideration, the host density dependence wasweak and non-significant. At the leaf level, acombined examination of both types ofheterogeneity in parasite distribution – hostdensity dependent heterogeneity (direct orindirect) and host density independentheterogeneity, was performed using the (CV)² > 1 criterion. The mean (CV)² value over different sampling dateswas greater than one. Host density independentheterogeneity had the greater contribution tostability. The (CV)² findings atleaf level in the plot, combining leaf and treeeffects, represent both aggregation at the treelevel (inverse density dependence) andaggregation at the leaf level (host densityindependence). The heterogeneity findings forparasitoid distribution, together with thestability, which was directly observed, supportour hypothesis that aggregation of risk is animportant mechanism in the stabilisinginteraction between the citrus whitefly and itsspecific parasitoid, E. lahorensis.     

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.