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.      

Biology ofEpidinocarsis [=Apoanagyrus] lopezi [Hymenoptera: Encyrtidae] an exotic parasite of cassava mealybug,Phenacoccus manihoti [Homoptera: Pseudococcidae] in Nigeria

The biology ofEpidinocarsis (=Apoanagyrus) lopezi (DeSantis) was studied under fluctuating laboratory conditions of 24–31°C and 79–90% R.H. It is a solitary internal parasite. There are 4 tailed larval instars. The total developmental time from egg to adult ranged from 11–25 days, average 18 days. The duration of each developmental stage was: egg 2 days, 1 st instar 1 day, 2nd instar 1 day, 3rd instar 2 days, 4th instar 2 days, prepupa 4 days and pupa 6 days. Males mated several times, females mated once. Mated females produced both males and females, unmated females produced only males. Mated ovipositing females lived for 13 days while non-ovipositing mated females lived for 25 days. Parasitization decreased with increasing host density from 30% at a density of 10 hosts/plant/female to 11% at a density of 50. There was virtually no pre-oviposition period. Based on 10 females, the highest mean daily progeny production was 10. Females have an average oviposition period of 11 days and an average of 67 adult progeny. The sex-ratio was 1∶2.3 in favour of females.     

Host finding byCryptolaemus montrouzieri (Col., Coccinellidae) a predator of mealybusgs (Hom., Pseudococcidae)

AdultC. montrouzieri were able to detect their prey by visual and chemical stimuli. Presence of mealybug caused a significant increase in the number of turns and a sharp decrease in flight attempts suggesting detection by olfaction. In the light, adult predators found polystyrene dummies significantly faster than under dark (red light) conditions, but light had no effect on the time taken for adults to pass across an invisible test point. Fourth instar larvae could only perceive the prey by physical contact.      

Étude de la consommation alimentaire d'Exochomus flaviventris (Col.: Coccinellidae) prédateur de la cochenille du maniocPhenacoccus manihoti (Hom.: Pseudococcidae)

Résumé Les besoins alimentaires de chaque stade de développement larvaire et des jeunes femelles d'E. flaviventris Mader ont été définis par rapport à deux cochenilles associées au manioc;:Planococcus citri Risso (proie locale) etPhenacoccus manihoti Mat.-Ferrero (proie exotique) dans les conditions de laboratoire (T=25°C±1°C; H.R.=80–90%; photopériode=L/D: 12/12). Ces deux proies constituent des ?nourritures essentielles? pourE. flaviventris qui les consomme en plus grande quantité par rapport aux autres coccinelles qui se nourrissent aux dépens, de la cochenille du manioc. Il faut en moyenne 71,8 mg de matière fra?che deP. manihoti (œufs+jeunes femelles) ou 86,9 mg deP. citri (œufs+jeunes femelles) àE. flaviventris pour atteindre le stade adulte. Dans chaque cas, les larves du prédateur de quatrième stade se montrent plus voraces avec plus de 70% de la consommation totale. Les jeunes, femelles consomment moins que les larves du dernier stade principalement quand il s'agit de la proie exotique. P. manihoti semble avoir été rapidement adoptée parE. flaviventris après son introduction accidentelle en Afrique. Sans être d'une valueur alimentaire exceptionnelle, elle est mieux exploitée que la cochenille indigène et procure un poids moyen de 10,9 mg aux adultes du prédateur à leur émergence.

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Summary Food requirements of each larval stage and of young females ofExochomus flaviventris have been defined regarding the two coccids associated to cassava:Phenacoccus citri (indigenous prey) andPhenacoccus manihoti (exotic prey) under laboratory conditions (25±1°C, 80–90% RH and L/D: 12/12). These 2 preys constitute the main food forE. flaviventris as this ladybird feeds on it much more than all the other coccinellids preying also on the cassava mealybug.E. flaviventris needs an average of 71.8 mg of freshP. manihoti (eggs and young, females) or 86.9 mg ofP. citri (eggs and young voracious with 70% of the total consumption. Young females feed less than the last instar larvae, especially when the exotic prey is involved. P. manihoti seems to have been rapidly choosen byE. flaviventris after its accidental introduction into Africa. Even if it is not an excellent prey from the food angle, it is better exploited thant the indigenous mealybug and adults of an average weight of 10.9 mg are obtained after emergence.

     

Economics of the cassava mealybug [Phaenacoccus Manihoti; Hom.: Pseudococcidae] biological control program in Africa

Critical analyses of current pest control practices and the role of classical biological control are needed. The costs and benefits of the introduction and release of natural enemies of the cassava mealybug are assessed. A conservative estimate shows that the benefit to cost ratio of this project is extremely high (149∶1).     

Evaluation of Serangium n. sp. (Col., Coccinellidae), a predator of Bemisia tabaci (Hom., Aleyrodidae) on cassava

Abstract  The potential of a new, previously unidentified Serangium species (Col., Coccinellidae) to control the high Bemisia tabaci (Gennadius) (Hom., Aleyrodidae) populations on cassava was evaluated. Field and laboratory studies were carried out to determine the abundance and feeding capacity of this Serangium species feeding on B. tabaci on cassava. Serangium nymphs and adults were most abundant in cassava fields late in the season, rising sharply from 5 months after planting (MAP) to a peak at 7–8 MAP. Pre-imaginal development averaged 21.2 days and was longest in eggs and shortest in the L₁ instar. Mean total prey consumption of immature Serangium increased with the stage of development with the lowest consumption in the L₁ instar and highest in the L₄ instar. Mean daily consumption was lowest on the first day after hatching in the L₁ instar and rose to a peak on the 13th day after hatching in the L₄ instar. Each Serangium larva consumed a mean of over 1000 nymphs during its entire development. These results have demonstrated the potential of this Serangium species to control B. tabaci populations on cassava.     

Life history of the importedScymnus (Nephus) Reunioni [Col.: Coccinellidae] predator of mealybugs

The life history ofNephus reunioni, introduced from the Reunioni island has been studied. Optimum temperature for the development of the entomophagous insect is 24–25°C. In this case the population has the highest survival at preimaginal stages, life duration of adults and reproductive capacity. The rate of population growth was calculated by the formula:

Introduction and evaluation ofChilocorus bipustulatus [Col.: Coccinellidae] for control ofParlatoria blanchardi [Hom.: Diaspididae] in date groves of Niger

Chilocorus bipustulatus L. was successfully established in oases of the Aïr Mountain region of Northern Niger (West Africa), where it became the major cause of mortality among adult females of the armored scaleParlatoria blanchardi Targioni-Tozzetti. This resulted in significantly lower scale infestation of date palms in a test plot when compared to a control with no introduced ladybeetles. The coccinellids were able to reproduce year-round, but during the hot season were largely confined to natural refuges composed of dense stands of date palms. Dispersal and multiplication occurred primarily during the rainy season, toward the end of which the greatest suppression of scale populations was seen.     

The establishment ofRhyzobius forestieri [Col.: Coccinellidae] in greece and its efficiency as an auxiliary control agent against a heavy infestation ofSaissetia oleae [Hom.: Coccidae]

Introduction releases of the exotic coccinellid predatorRhyzobius forestieri Mulsant were made in 22 localities throughout Greece. The releases were made on olive, citrus, fig and almond trees infested with differentCoccidae scales. In 9 of these localities,R. forestieri was recovered 2–5 months later. The most important factor for the successful establishment ofR. forestieri seems to be an abundance of scales on the trees. To study the ability ofR. forestieri to enhance overall predation, 3 releases were made in an olive grove heavily infested withSaissetia oleae Olivier on Chios island during 1982 and 1983. The experiment began in June 1982. By April 1983, theS. oleae infestation was clearly in the process of being controlled by the coccinellid. A native coccinellid,Exochomus quadripustulatus L., contributed little during this period because of its obligatory estival diapause. The other main coccinellid,Chilocorus bipustulatus L., made an appreciable contribution toward achieving control during the summers of 1982 and 1983, but it was affected from July onward by increasing parasitism of its larvae. Both species are quiescent during the winter months. The introduced speciesR. forestieri was readily established in the olive grove and multiplied quickly. One month after the initial release,R. forestieri larvae made up most of the coccinellid larval population in the field. Thereafter until April 1983,R. forestieri larvae and adults comprised the dominant coccinellid population in the olive grove. During the winter months,R. forestieri remains active as long as temperature exceeds 8 °C. The important increase inR. forestieri's population size between July 1982 and April 1983 coincided with the increased rate of predation onS. oleae. This suggests thatS. forestieri played a key role in bringing theS. oleae infestation under control during this period. After April 1983, however, theR. forestieri population diminished rapidly andC. bipustulatus became the dominant coccinellid in the olive grove. It is believed that scarcity of prey was the cause of this reversal: by April 1983, the density ofS. oleae in the olive grove had already been reduced by about 100 times.     

Interaction betweenRastrococcus invadens [Hom.: Pseudococcidae] and two natural enemies

Two natural enemies of the mealybugRastrococcus invadens, the parasitoidGyranussoidea tebygi and the pathogenHirsutella cryptosclerotium were tested. Levels of parasitism by the parasitoid were reduced by the pathogen but overall mortality of the mealybug was greater both when agents were acting together.      

The natural enemies of the armored scale lady-beetleChilocorus bipustulatus [Col. Coccinellidae]

The most common parasite ofC. bipustulatus larvae and pupae in Israel isH. flaminius [Hym., Encyrtidae]. A theory of the survival of hyperparasites through a mechanism which prevents overlapping of appearance was presented. The parasites, predators and pathogens which were found as well as those reviewed in the literature explain the low value ofC. bipustulatus in biological control of scale-insects in groves.

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Résumé Le parasite le plus commun des larves et des nymphes deC. bipustulatus en Israel estHomalotylus flaminius (Encyrtidae). Il a été montré expérimentalement que deux autres espèces,Achrysopophagus aegyptiacus etPachyneuron siculum, sont des hyperparasites des larves deH. flaminius. Il est présenté une théorie de la survie des hyperparasites à l'aide d'un mécanisme qui empêche les chevauchements d'apparition. Les autres hyménoptères parasites nouveaux, les fourmis les fourmilions et les champignons pathogènes ont une importance secondaire dans la réduction des populations deC. bipustulatus. Les parasites, prédateurs et pathogènes que nous avons trouvés aussi bien que ceux mentionnés dans la littérature expliquent la faible valeur deC. bipustulatus pour la lutte biologique contre les cochenilles en vergers.

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Research financed in part by grant No. FG.-Is-227, U.S.D.A.     

Biological control of the cassava mealybug Phenacoccus manihoti (Hom., Pseudococcidae) by Epidinocarsis lopezi (Hym., Encyrtidae) in Malawi

From 1985 to 1989 five large scale surveys were made to document the spread of the cassava mealybug (CM) Phenacoccus manihoti Matile‐Ferrero (Hom., Pseudococcidae) and the releases and successful establishment of its exotic parasitoid Epidinocarsis lopezi (De Santis) (Hym., Encyrtidae) through most cassava‐growing areas of Malawi. In a multiple regression analysis involving 29 meteorological, agronomic and plant variables from 476 fields, the duration of E. lopezi's presence was the major factor influencing CM population densities. In the first year the CM was recorded in a particular place, 25% of all tips had more than 100 CM. Wherever E. lopezi had been present for two years or more, CM populations were reduced on average seven times and tips infested with more than 100 CM became rare (1%). In parallel, damage on cassava tips stabilized at a low level. Similarly, along Lake Malawi, 84.9% of all tips had more than 10 CM in 1986; this value stabilized at 3.3%‐4.0% in 1988–1989. Indigenous coccinellids were often abundant in the first year of the CM infestation, but their populations collapsed later, while the frequency of fields with E. lopezi increased. In 1987, farmers abandoned 28.4% of all fields where E. lopezi was just introduced as compared with 2.7% where the parasitoid had been present for two years or more. Overall, satisfactory control was achieved by E. lopezi in all but a few fields concentrated on extremely poor soils characterized by sand dune vegetation. The socioeconomic implications of this ongoing and apparently successful biological control program are discussed.     

Laboratory rearing of the predatory coccinellidCleobora mellyi [Col.: Coccinellidae] for biological control ofParopsis charybdis [Col.: Chrysomelidae] in New Zealand

Cleobora mellyi Mulstant has been introduced into New Zealand in an attempt to controlParopsis charybdis Stål. Artificial diets and a practical method for rearing the predatory Australian ladybird,C. mellyi, are described.     

The observed sex ratio ofPediobius foveolatus [Hym.: Eulophidae] in field populations ofEpilachna varivestis [Col.: Coccinellidae]

Larvae ofEpilachna varivestis Mulsant, parasitized byPediobius foveolatus (Crawford), were collected in soybean fields in Maryland during 1975. AdultP. foveolatus emerging from the larvae were sexed and counted. The ratio of males to females increased as the availability of food within the host decreased. This information is useful in development of exponential models predicting hostparasite interactions.     

Trophic regulation of postdiapause ovariole maturation inCoccinella septempunctata [Col.: Coccinellidae]

In 1977 the vernal maturation ofCoccinella septempunctata L. females was investigated in relation to the variation in aphid population density on alfalfa and cereals in central Bohemia. The ovarioles do not ripen unless the aphid population density reaches a certain threshold. This leads to considerable variability in the time of vernal reproductive activity (up to 1.5 months in the same geographic locality) among subpopulations living on crops with different aphid densities. This mechanism enables the reproduction of the aphidophagous insect to synchronize with the population development of the aphid.     

Étude de l'évolution d'une mycose aNeozygites fumosa [Zygomycetes,Entomophthorales] dans une population de la cochenille du manioc,Phenacoccus manihoti [Hom.: Pseudococcidae]

Résumé L'action régulatrice d'un champignon du groupe des Entomophthorales,Neozygites fumosa (Speare) Remaudière et Keller, est mise en évidence pour la lère fois dans une population de la cochenille du maniocPhenacoccus manihoti Matile-Ferrero (Homoptères: Pseudococcidae) en République Populaire du Congo en 1982. Le pathogène est de loin l'ennemi naturel qui intervient le plus significativement dans la régulation des effectifs. L'extension de la maladie dans la population h?te appara?t conditionnée par l'apparition simultanée d'une humidité relative supérieure ou égale à 90% et d'une température journalière minimale supérieure à 20°C. Elle semble également liée à la densité du ravageur. On notera enfin que les formes adultes sont systématiquement plus infectées que les formes larvaires.

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Summary The regulatory action of the entomophthoraceous fungusNeozygites fumosa (Speare) Remaudière & Keller (Zygomycetes) is shown for the ist time in a population of the Cassava mealybug,Phenacoccus manihoti (Hom.: Pseudococcidae), in the People's Republic of the Congo in 1982. This pathogen is by far the natural enemy which intervenes the most significantly in the regulation of this insect. The development of the epizootic appears to be influenced by a relative humidity of at least 90% along with a minimal daily temperature greater than 20°C. The spread of the disease also seems to be affected by the host density. Throughout the entire duration of this study, the adult forms were more infected than the larval forms.

     

Importation,colonization and establishment ofAnagyrus indicus [Hym.: Encyrtidae] onNipaecoccus viridis [Hom.: Pseudococcidae] in Jordan

Anagyrus indicus Shafeeet al. was collected on the island of Guam and released in the Jordan River Valley of Jordan in order to regulateNipaecoccus viridis (Newstead) on citrus.A. indicus was originally released in February 1984 and became colonized by April of the same year. It also dispersed by natural means up to 61 km following the original release and colonized that same year on infestedZizyphus sp. By spring of 1985 it became the dominant parasitoid attackingN. viridis. Another parasitoid,Anagyrus kamali Moursi, was collected in Jordan in June of 1985 for the first time. This latter parasitoid apparently moved into the Jordan River Valley by means of natural dispersal from a neighboring country. Infestations ofN. viridis have been greatly reduced in areas whereA. indicus became established. This paper reports the results of research only. Mention of a proprietary product does not constitute an endorsement for its use by USDA.     

Preference for medium dense grass tussocks byHippodamia convergens [Col.: Coccinellidae]

The preference in the choice of hibernacula of the convergent lady beetle,Hippodamia convergens Guérin-Meneville, was investigated with regard to morphological aspects of 2 introduced range grasses,Panicum coloratum (L.), andEragrostis curvula (Schrad.) Beetles strongly preferred tussocks with a ratio in the range of 1.0–3.0 stems per cm² for lovegrass. Preference for klein grass tussocks ranging from 110–130 stems/clump was found. No preference was shown for a particular tussock circumference. It was demonstrated that tussocks could successfully be designated as suitable for beetle aggregation.     

Brinckochrysa scelestes [Neur.: Chrysopidae] as predator ofMyzus persicae [Hom.: Aphididae] on tobacco

Laboratory and field studies were conducted to study the suitability and efficacy ofBrinckochrysa scelestes Banks as a predator onMyzus persicae Sulzer in tobacco fields. Laboratory bred 2nd instar larvae ofB. scelestes at 6 per tobacco plant reduced the aphid population to the extent of 78% in 2 weeks. The movement of the predatory larvae on the tobacco plant and leaf was not at all hampered by the glandular trichomes and their secretions. The larvae moved freely and fed well and their pupae were recovered from all over the plant.

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Résumé On étudie en laboratoire et en champ de tabac la valeur et l'efficacité deBrinckchrysa scelestes Banks comme agent de lutte biologique contreMyzus persicae Sulzer. Les larves du 2ème stade élevées en laboratoire de ce chrysope à raison de 6 par plante sont les plus actives et réduisent la population de pucerons de 78% en 2 semaines. Les sécrétions des trichomes des feuilles de tabac n'ont pas d'effet sur les larves ni sur leurs mouvements. Les larves se déplacent librement et se nourissent bien; des nymphes ont été trouvées sur tous les plants, ce qui indique que le prédateur est valable contreM. persicae et bien adapté à la culture de tabac.