Development and encapsulation of the endoparasitoid,Microplitis croceipes (Hym.: Braconidae), in six candidate host species (Lep.)

Encapsulation and development of the endoparasitoid,Microplitis croceipes (Cresson), were studied in six atypical lepidopteran host species whose usual host isHelicoverpa zea (Boddie). The candidate hosts examined were: the fall armywormSpodoptera frugiperda (J. E. Smith); the beet armyworm,Spodoptera exigua (Hübner); the cabbage looper,Trichoplusia ni (Hübner); the greater wax moth,Galleria mellonella (L.); the Indian meal moth,Plodia interpunctella (Hübner); and the diamondback moth,Plutella xylostella (L.). BothS. exigua andT. ni were completely unsuitable forM. croceipes development due to the high rate of eggs that were encapsulated within three days after parasitism. Encapsulation inS. frugiperda included mainly parasitoid eggs and was first detected six days after parasitization at 25°C and two days at 30°C. Encapsulation inG. mellonella occurred only in the larval stage of the parasitoid. InP. interpunctella, parasitoid larvae reached the 3rd stadium, but none of them pupated. OnlyS. frugiperda andG. mellonella supported successful development ofM. croceipes from egg to adult. The percentage of parasitoids reaching the adult stage in these hosts was higher at 30°C than at 25°C (13% vs. 4% inS. frugiperda, and 21% vs. 3% inG. mellonella, respectively). However, these percentages were too low to substitute them as a more economical host for rearingM. croceipes. This biological information will be useful in additional laboratory studies directed toward reducing the rate of encapsulation (e.g., manipulation of host rearing temperature) to increase production ofM. croceipes on these hosts.     

Influence of crucifer cropping system on the parasitism ofPlutella xylostella (Lep., Yponomeutidae) byCotesia plutellae (Hym., Braconidae) andDiadegma semiclausum (Hym., Ichneumonidae)

Field experiments were conducted to study the influence of cabbage monoculture and mixed cropping on the parasitism of diamondback moth,Plutella xylostella (L.), a destructive pest of all crucifers, by 2 larval parasites,Diadegma semiclausum Hellén andCotesia plutellae Kurdjumov. There was no significant difference in parasitism by either species whether cabbage was planted in insecticide-free monoculture or in mixed cropping with 8 noncrucifers which were sprayed twice a week with chemical insecticides mevinphos, methamidophos and permethrin. Population ofP. xylostella increased as the cabbage plants grew older. Parasitism byC. plutellae was higher soon after cabbage transplanting but decreased as the plants grew older. Parasitism byD. semiclausum was very low soon after cabbage planting but increased as the plants grew older. A significant negative correlation was found betwen parasitism byC. plutellae andD. semiclausum. In a caged field study where only one parasite species was used in an individual cage, parasitism ofP. xylostella by both species decreased as theP. xylostella population increased. This is believed to be due to the absence of competition between the two parasites inside the cage. There was no relationship between host-plant age and parasitism ofP. xylostella larvae by either parasite species.     

Classical biological control ofaleurocanthus spiniferus (Hem.: Aleyrodidae), on citrus in Southern Africa

The spiny blackfly,Aleurocanthus spiniferus (Quaintance), is a citrus pest in parts of Mpumalanga, South Africa, and in Swaziland. The leaves, fruit and branches of infested trees are usually covered with sooty mould and a reduction in tree vigour and production is experienced. Classical biological control ofA. spiniferus by the parasitoid,Encarsia cf.Smithi (Silvestri) (Hym.: Aphelinidae) is reported with a significant reduction in numbers ofA. spiniferus. The parasitoid dispersed successfully from isolated trees growing in home gardens andA. spiniferus was virtually eliminated up to 0,8 km from the nearest point of release within 10 months. A mean of 72.9% parasitism was reached. In 8 months,E. cf.smithi statistically reduced theA. spiniferus in parts of a commercial orchard where it was released, reaching 82.4% parasitism.     

Involvement of larvicidal toxins in pathogenesis of insect parasitism with the rhabditoid nematodes,Steinernema feltiae andHeterorhabditis bacteriophora

The insect-parasitic rhabditoid nematodes,Steinernema feltiae andHeterorhabditis bacteriophora, released a compound/s/ toxic to larvae of the greater wax moth,Galleria mellonella, that caused paralysis and death of the insect. Larvicidal substances appeared in wax moth larvae during parasitism and after inoculation with the primary form of the bacterial associates of the nematodes. The nematodeS. feltiae and its associate,Xenorhabdus nematophilus, excreted much less toxic activity within larval body thanH. bacteriophora. The secondary form ofXenohabdus did not produce toxin in parasitized larvae, butX. luminescens, the bacterium associated withH. bacteriophora, released detectable titer of toxin activity in broth cultures. Both nematode toxins were sensitive to heat and produced a specific type of proteolytic activity. Preliminary identification of the compounds responsible for larval toxicity revealed similarities to immune inhibitors produced by some bacterial pathogens of insects.      

Ectoparasitic Acugutturid Nematodes of Adult Lepidoptera

Noctuidonema guyaneme is an interesting ectoparasite of adult Lepidoptera that feeds on hosts from at least five families with its long stylet. Noctuidonema guyanense spends its entire life on the adult moth and is sustained as it is passed from moth to moth during host mating. Overlapping host generations are essential for parasite survival. This nematode occurs throughout tropical and subtropical America and is transported by at least one of its hosts, Spodoptera frugiperda, during migration to northern sites in the United States each spring. Noctuidonema guyanense debilitates its hosts. Research conducted to help determine the biological control importance of this nematode is reviewed. Two additional species, N. daptria and N. dibolia, are now known for Noctuidonema.     

Host specificity ofPareuchaetes insulata (Lep.: Arctiidae), a biological control agent forChromolaena odorata (Compositae)

Larvae of the arctiid moth,Pareuchaetes insulata, from Florida fed on the leaves ofChromolaena odorata, a serious composite, alien weed in Natal, South Africa. In starvation test trials using 48 plant species,P. insulata completed its development onC. odorata andAgeratum houstonianum. Subsequent attempts to cultureP. insulata on these two plants was only successful onC. odorata. The biology ofP. insulata is similar to that of two other well studiedPareuchaetes species namelyP. pseudoinsulata andP. aurata aurata. Repeated defoliation ofC. odorata byP. insulata could contribute to its control as has been found withP. pseudoinsulata in Guam.Pareuchaetes insulata has been approved for release as a biological control agent ofC. odorata in South Africa.     

Parasitism ofTrialeurodes ricini byEncarsia formosa: Level of parasitism,development time and mortality on different host plants

The effects of the host plant on the level of parasitism, development time and mortality ofEncarsia formosa Gahan parasitizing castor whitefly,Trialeurodes ricini Misra were studied. The level of parasitism varied significantly between host plants; ranging from an average high of 13/50T. ricini larvae parasitized per parasitoid per day on aubergine to an average low of 1.6/50 host larvae on potato. Development time ofE. formosa varied according to whitefly host plant; minimum average development time was 17.7 days on cotton. The mortality ofE. formosa was high on all host plants tested, and the type of host plant had no significant influence on mortality. Aubergine proved to be the most satisfactory laboratory plant for rearingE. formosa onT. ricini.     

Quantification of Invasion of Two Strains of Steinernema carpocapsae (Weiser) into Three Lepidopteran Larvae

Studies with last instar larvae of the fall armyworm, Spodoptera frugiperda (J. E. Smith), the black cutworm, Agrotis ipsilon (Hufnagel), and the greater wax moth, Galleria mellonella (L.) were used to quantify the invasive ability of two strains (All and Mexican) of Steinernema carpocapsae and to determine how factors in the bioassay procedure affect both nematode invasion and host mortality. Nematode invasive ability was variable, with 10-50% of nematodes successfully infecting the host. The percentage of infectives invading the host (invasion efficiency) was positively related to increases in length of host exposure time and number of hosts per arena, negatively related to increases in substrate surface area per host, and not affected by nematode concentration. There was a direct relationship between concentration applied and the number of nematodes invading the host. Mortality was less affected than invasion efficiency by bioassay conditions and appears to be a much less sensitive index of nematode activity than invasive ability.     

Parasitism of different larval stages of Cameraria ohridella

About 20 species of parasitic Hymenoptera havebeen reported from the horse chestnutleafminer, Cameraria ohridella Deschka & Dimic (Lepidoptera: Gracillariidae). Generally,parasitism is low compared to other closelyrelated leafminers and the parasitism levelvaries considerably. Among other reasons,parasitism rates depend on the developmentalstage of the moth and therefore vary with thesampling date. In the current study,investigations on the parasitism of the moth'sfirst generation were carried out in order todetermine which preimaginal stages areparasitized by the most abundant parasiticwasps. Minotetrastichus frontalis (Nees),Pnigalio agraules (Walker) and Chrysocharis nephereus (Walker) (allHymenoptera: Eulophidae) developed as larval orpupal parasitoids and preferred later larvalinstars of the moth. Egg parasitism did notoccur. Overall, the last two of the six larvalinstars (the spinning instars) of the leafminersuffered the heaviest attack. In concordancewith the fairly low parasitism rates, theeffect of the four most abundant chalcidoids onthe leafminer population was negligible, havingno significant influence on the mortality ofC. ohridella. Although the speciescomposition of the parasitoid complex of C. ohridella shows similarities with thesituation found in other closely relatedleafmining moths, it is unlikely that thenaturally occurring chalcidoids will be able toprevent the horse chestnut leafminer fromdeveloping epidemic population densities in thenear future.     

Biology ofTrichogramma ostriniae (Hym.: trichogrammatidae) reared onOstrinia nubilalis (Lep.: pyralidae) and survey for additional hosts

Trichogramma ostriniae has been identified as a candidate for biological control ofOstrinia nubilalis. As little was known about the biology of this parasitoid when reared onO. nubilalis, we undertook experiments to quantify biological parameters important to mass-rearing and ase ofT. ostriniae. When reared continuously onO. nubilalis, femaleT. ostriniae on average lived 2.7 days and produced 24 progeny. Continuous access to honey resulted in a four-fold increase in longevity and fecundity and a significant increase in the percentage of females parasitizing eggs. Rates of fecundity and parasitism decreased with age of female. Likewise, emergence rates and percentage of female progeny decreased with age of parental female.T. ostriniae successfully parasitizedO. nubilalis eggs until the blackhead stage. Most parasitism of eggs and eclosion of adults occurred during the first half of photophase. Eggs of 13 Lepidopterans were parasitized byT. ostriniae. Eggs of the Noctuidae, Pyralidae, and Plutellidae experienced higher levels of parasitism than others tested.T. ostriniae appears to be similar to other species ofTrichogramma in several respects and does not possess any characteristics that limit its potential for mass rearing and use for augmentative biological control ofO. nubilalis.     

Pollination ofDianthus gratianopolitanus (Caryophyllaceae)

Pollination ofDianthus gratianopolitanus was studied in a population of the Swiss Jura mountains. Pollinators of this plant species are reported here for the first time. The flowers were not only visited by butterflies as postulated in the literature, but also by diurnal hawkmoths (Macroglossum stellatarum) and by diurnal and nocturnal noctuid moths. — Nectar is sucrose-dominant, the sugar concentration is moderate but the amino acid concentration is high. Nectar characteristics correspond well with the syndrome ofLepidoptera-pollinated flowers. — Field observations and flower characters (colour, range of the calyx length) suggest thatDianthus gratianopolitanus is an intermediate species in the transition of butterfly to moth pollination. — Lack of reproductive success inDianthus gratianopolitanus can not be attributed to lack of suitable pollinators.     

Aleochara suffusa andA. bilineata (Col.: Staphylinidae) as parasitoids of brassica root flies in northern Norway

A sample ofDelia puparia collected in late autumn from a brassica field at Tromsø, northern Norway, was investigated to study the level of parasitism byAleochara. BothA. suffusa andA. bilineata were reared from puparia of the cabbage root fly,Delia radicum, and the bean seed flies,D. florilega and/orD. platura. Only two specimens ofA. bilineata emerged from puparia of the turnip root fly,D. floralis. BothAleochara species hibernated in the larval state and both pupated inside the host puparium. Most specimens ofA. suffusa emerged from small hosts (D. florilega/D. platura), whereas the majority of A.bilineata emerged from host species of larger size (D. radicum/D. floralis). The time to develop from first instar larva to adult was similar for bothA. suffusa andA. bilineata. Parasitoids developing in large hosts emerged later than those in small hosts, the delay being the same for both species ofAleochara.     

Factors influencing parasitism of Sirex noctilio (Hymenoptera: Siricidae) by the nematode Deladenus siricidicola (Nematoda: Neotylenchidae) in summer rainfall areas of South Africa

Control of the invasive wasp, Sirex noctilio Fabricius using the parasitic nematode Deladenus siricidicola Bedding is a well known example of a successful classical biological control program. Despite its wide-scale success, this control method has recently had poor success in the summer rainfall areas of South Africa. Data from previous studies showed variation in nematode parasitism from inoculated trees (inoculation success) between different tree sections and among inoculation times. They also pointed to moisture content of the wood or virulence of the nematode as the most likely underlying factors influencing variations in inoculation success. The results from our study showed that the highest levels of parasitism was obtained from early inoculations and from the bottom sections of trees, where moisture content of the wood was highest, supporting the hypothesis that moisture content influences parasitism. However, even when moisture content was adequate, average inoculation success remained below 25% and was often 0%, suggesting that there are other barriers to inoculation success. Different sources from which the nematodes were produced did not influence inoculation success, indicating that nematode virulence is most likely not the cause of the low success. Another interesting finding was that parasitized wasps were larger than unparasitized wasps. Background parasitism was present despite the poor success with past inoculations, but the data also suggest that the natural build-up of this population could be constrained by the same factors that influence inoculations.     

Life histories ofPsyllaephagus yaseeni (Hym., Encyrtidae) andTamarixia leucaenae (Hym., Eulophidae), parasitoids of the leucaena psyllidHeteropsylla cubana

Age specific fecundity of two parasitoids,P. yaseeni andT. leucaenae, of the leucaena psyllidH. cubana, were studied under laboratory conditions. At 25 °C,P. yaseeni had a greater fecundity (R₀=192.9)_thanT. leucaenae (R₀=71.2);T. leucaenae however had a lower sex ratio (about 99 % females) thanP. yaseeni (about 50 % females). Innate capacity for increase (r_m=0.236) ofT. leucaenae was higher thanP. yaseeni (r_m=0.188). Developmental rates of the parasitoids were examined at constant and fluctuating temperatures and equations of the rate of development against temperature were calculated. At 25 °C, mean generation times were 28.0 and 18.1 days forP. yaeseeni andT. leucaenae respectively. At temperatures of 21.5, 25, and 30 °C total development times (egg to adult) were 28.5, 21.9, and 14.7 days inP. yaseeni and 19.2, 12.6, and 9.5 days inT. leucaenae respectively. The level of parasitism was low and pupal mortality was high at the lower temperature of 21.5 °C for both parasitoids. Both parasitoids showed poor survivorship at 100 % RH,P. yaseeni survived particularly well (32 days) at a temperature of 21.5 °C and 44 or 76 % RH. P. yaseeni allocated about 58 % females to first instar psyllid nymphs but only 12 % females to second instars. About 99 % of allT. leucaenae births were females. Significantly largerT. leucaenae females emerged from fifth instar parasitized nymphs than third or fourth instars.     

Parasitism ofLygus lineolaris eggs onCoronilla varia,solanum tuberosum,and three host weeds in southeastern Québec

Parasitism ofLygus lineolaris (Palisot de Beauvois) eggs by three species ofMymaridae, Anaphes iole Girault,Erythmelus miridiphagus Dozier andPolynema pratensiphagum Walley and one species ofScelionidae, Telenomus sp., was investigated at Ste-Anne-de-Bellevue, Québec. The maximum level of field parasitism ofL. lineolaris eggs by individual species was 15.4, 53.8, 70.0 and 16,7%, respectively. Parasitoids were retrieved from eggs ofL. lineolaris inserted in stems and branches ofAmaranthus retroflexus L.,Chenopodium album L.,Coronilla varia L.,Rumex obtusifolius L. andSolanum tuberosum L. Amaranthus retroflexus andS. tuberosum sustained a large population ofL. lineolaris and egg parasitism was high enough to consider it as a potential control factor.      

Influence of the chickpea cropping system onHelicoverpa armigera (Lep.: noctuidae) populations and their rate of parasitism byCampoletis chlorideae (Hym.: ichneumonidae)

The effect of intercropping chickpea with coriander or linseed onHelicoverpa armigera Hübner egg and larval populations and on the rate of larval parasitism was examined. There were significantly moreH. armigera larvae per plot in the sole chickpea treatment than in the intercropped treatments. The reduction was not the result of a negative effect of the companion crops on the numbers of larvae attacking chickpea. Larval density on chickpea was higher in the intercropped plots than the plots of sole chickpea. The presence of the flowering companion crops did not result in either the attraction of otherwise uncommon parasitoids to the crop or an increase in the proportion ofH. armigera larvae parasitized byCampoletis chlorideae Uchida. The results suggest that chickpea is a more suitable host forH. armigera than coriander or linseed, and that the reduction in the density ofH. armigera larvae in the intercroped treatments was due to the lower number of chickpea plants in these treatments.     

Incidence and ecological relationships of pupal parasitism byBrachymeria intermedia in new Jersey populations of the gypsy moth

Pupal parasitism of the gypsy moth,Lymantria dispar (L.), was monitored in 15 study plots in New Jersey from 1978 to 1988. The predominant parasitoid was a chalcidid wasp,Brachymeria intermedia (Nees), which was found in only six plots. Parasitism was generally observed in the year of or preceding the peak numbers of gypsy moth egg masses. Parasitism exceeded 4% in only one plot. Percentage parasitism was correlated significantly with numbers of egg masses per hectare in the current season and with numbers of pupae per plot in the previous season, suggesting delayed density dependence. A multiple regression analysis found percentage parasitism to be correlated significantly with percentage infection by nuclear polyhedrosis virus, density of male host pupae, and mean minimum temperature in August and March. A canonical discriminant analysis carried out to distinguish study plots with and without the parasitoid was significant. Plots withB. intermedia had relatively higher host populations and defoliation.     

Changes in abundance of native and introduced parasites (Hymenoptera: Braconidae), and of the target and non-target plant bug species (Hemiptera: Miridae), during two classical biological control programs in alfalfa.

High numbers of tarnished plant bugs [Lygus lineolaris (Palisot)], were once common in alfalfa, as was a low level of parasitism (9%) by the native Peristenus pallipes (Curtis). After the bivoltine European parasite Peristenus digoneutis Loan became well established, average parasitism of the first and second generations increased to 64%, and tarnished plant bug numbers dropped by 65%. This reduced host density eventually caused a decline in total parasitism by both parasite species to 22%. A few P. digoneutis also attacked the alfalfa plant bug, Adelphocoris lineolatus (Goeze), but did not reduce this pest or increase its parasitism rate. At another location, where P. digoneutis is not established, parasitism of first generation alfalfa plant bugs, an adventive (accidently introduced) pest, was increased to 21% by the introduced univoltine parasite, Peristenus conradi Marsh, and a slight reduction in the pest may have resulted. P. digoneutis did not parasitize the meadow plant bug, Leptopterna dolabrata (L.), an adventive pest of forage grasses, so did not affect this mirid or its parasite. Neither introduced parasite eliminated the native parasites of the tarnished or alfalfa plant bugs. The narrow host ranges of the braconid parasites of mirid nymphs are contrasted with the broad host range of the native tachinid parasite [Phasia robertsoni (Towns.)] of adult mirids. The major changes in mirid abundance and their mortality by parasites that slowly occurred during this 19-year study demonstrate the need for long-term field research, to adequately document and understand these complex interactions.     

Biology ofPterolonche inspersa (Lep.: Pterolonchidae), a biological control agent forCentaurea diffusa andC. maculosa in the United States

The moth,Pterolonche inspersa (Staudinger) (Lepidoptera: Pterolonchidae), is widely distributed in southern Europe, north Africa, Turkey and the former Soviet Union. It occurs in both thick and scattered stands of knapweeds in disturbed sites, usually on sandy and/or stony soil. Larvae bore in the roots of diffuse and spotted knapweeds (Centaurea diffusa De Lamarck andC. maculosa De Lamarck). There is one generation per year in northern Greece, and larvae feed in the roots for about 11 months during the growing season (August–September, to the following July–August). In the laboratory garden, emergence took place between the second half of July and the end of August, with peak emergence during mid August. In the field, adults were observed from early to late July. Female moths oviposited on rosettes during the first ten days of July and continued through the end of July. Eggs were laid singly or in groups of five or six, firmly attached to the leaves of the host plant. In the laboratory, females mated within 24 hours of emergence and the preoviposition period lasted 2.6±0.8 days. The oviposition period lasted 7.4±2.2 days and the average number of eggs per female was 142.2±59.2. The incubation period was 12±4.7 days; the pupal stage lasted 14.7±2.4 days; and females lived 15.8±2.4 days, while males lived 10.7±1.4 days. First instar larvae failed to survive on economically important Compositae in the generaCynara L.,Helianthus L.,Zinnia L. andCalendula L. (Dunnet al., 1989).