Parasitoid Activity Research Articles

Parasitization of House Fly Pupae (Diptera: Muscidae) bySpalangia nigroaenea(Hymenoptera: Pteromalidae) in Cattle Feedlot Environments

Abstract Spalangia nigroaenea Curtis, a parasitoid that attacks filth fly pupae, has been mass-released for biological control in western Kansas. The influence of three different variations of the parasitoid-to-host ratio on parasitism of house fly, Musca domestica L., pupae was studied under feedlot conditions from 1993 to 1995. When a single parasitoid female was introduced to containers with varied host densities, the highest percentage of parasitization occurred at densities of 15 (1993 and 1994) and 10 (1995) puparia. When the ratio of parasitoid-to-host was changed, increasing densities from 30 to 300 for the host and from 3 to 30 for the parasitoid did not significantly affect performance of the parasitoid. Finally, parasitoid densities were varied, while host densities were held constant. Although significantly more offspring were produced as the parasitoid-to-host ratio changed from 1:5 to 1:50, the percentage parasitism actually decreased. The third measure of parasitoid activity, parasitoid-induced mortality (PIM), also was examined. In 1994, PIM did not differ significantly with the changing parasitoid-to-host ratios. However, in 1995 a direct correlation occurred between PIM and parasitoid-host-ratios. During the fly breeding season (May to October in 1994), the daily maximum temperature was correlated negatively with parasitism. Clearly, physical factors (mainly temperature) and biological factors (such as interspecific competition) are important in determining the success of mass release programs. The conflict between the efficiency and the effectiveness of biological control of filth flies using pteromalid parasitoids is discussed.

Saturated hydrocarbons as kairomonal source for the egg parasitoid, Trichogramma chilonis Ishii (Hym., Trichogrammatidae)

Abstract: Studies on the effect of saturated hydrocarbons on parasitization by the egg parasitoid Trichogramma chilonis Ishii were carried out in the laboratory and net house. Bioassay of 11 hydrocarbons, viz. pentadecane, heptadecane, ecosane, heneicosane, docosane, tricosane, tetracosane, pentacosane, hexacosane, octacosane and hexatriacontane, were carried out under controlled conditions in the laboratory. These were also tested on potted maize plants in a net house. Among the saturated hydrocarbons, octacosane recorded the highest parasitoid activity index followed by docosane and tricosane. However, tricosane caused the highest percentage of parasitization, which was at par with octacosane and docosane. A positive correlation was found between concentration and kairomonal activity only in case of tricosane. In the net house, tricosane recorded the highest parasitization. Response of the parasitoid to egg cards treated with hydrocarbons decreased with increase in distance between the release point and host eggs. No parasitization was observed in host eggs placed at 8 m and 10 m away from the point of release except in the case of tricosane and pentacosane.

Tritrophic interactions between host plants, the cassava mealybug Phenacoccus manihoti Matile‐Ferrero (Horn., Pseudococcidae) and its parasitoid Apoanagyrus lopezi De Santis (Hym., Encyrtidae)

Abstract: The influence of the host plant on the parsitism of third instar Phenacoccus manihoti Matile‐Ferrero by Apoanagyrus (Epidinocarsis) lopezi De Santis, was investigated under laboratory conditions. Four different host plants were used: two cassava varieties (Incoza and Zanaga, Manihot esculenta Crantz, Euphorbiaceae), the Faux caoutchouc (FC) (a hybrid of M. esculenta and Manihot glaziovii, Euphorbiaceae) and Talinum (Talinum triangularae Jack., Portulacaceae). The percentage of parasitism of P. manihoti by A. lopezi varied significantly between host plants and was 1.5 to 1.8 higher on Talinum than on the plants of the Manihot genus. The parasitism on Incoza did not differ from the one on Zanaga but was significantly higher than that on FC. The percentage of mummified hosts also differed among the four plants and was lower on FC (80.5%) than on the others. A significantly lower percentage of emerged parasitoids (69.5%) was recorded with the Incoza variety, which was the most resistant cassava plant. The total mealybug mortality due to parasitoid activity was significantly higher on Talinum than on the others. The results for the Manihot plants suggest that the probability of achieving successful augmentative biological control will be greater on the plants of the M. esculenta species despite lower A. lopezi survival on Incoza due to its high level of antibiosis resistance. Talinum would be a better host plant for a mass rearing of the host and the parasitoid in the laboratory.

Kairomonal Effects of Different Host Body Washings on Parasitism by Trichogramma brasiliensis and T. japonicum

Bioassays were carried out in Petri dishes with body washings of larvae, male and female moths and scale extract of Corcyra cephalonica St. in hexane to observe their kairomonal effect on Trichogramma brasiliensis (Ashmead) and T. japonicum Ashmead. The mean parasitoid activity index (PAI) and mean parasitisation were recorded. Trichogramma brasiliensis and T. japonicum recorded the highest mean parasitisation in the eggs treated with scale extract. Mean parasitisation recorded by T. japonicum in cards treated with female moth and male moth body washings were considerably lower than the corresponding values for T. brasiliensis . Both the parasitoids recorded significantly lower levels of parasitisation in cards treated with larval body washings. Gas chromatographs of host body washings / extract recorded a large number of similar hydrocarbons in the body washings of male and female moths and the scale extract. Pentadecane, heneicosane, eicosane, tetracosane, pentacosane and hexacosane were recorded in scale extracts. Female moth body washings recorded the presence of eicosane, tetracosane and pentacosane while heneicosane and eicosane were indicated in the male moth body washings.

Activité saisonnière et distribution des parasitoïdes de pucerons du froment d’hiver

Activity of antagonists in winter and early spring as well as in late summer and autumn plays an important role in the control of cereal aphid populations. Indeed, parasitoids active early in the year are important to avoid high aphid densities. Late summer and autumn correspond to the transition period between two wheat cultures, and parasitoid activity would thus reduce aphid infestation. During these critical periods, other crops like rye-grass and red clover containing alternative hosts could play the role of parasitoid reservoirs. During 1996, parasitoid activity was measured by trap planting in wheat, rye-grass, red clover and fallow grassland. In each plot, early spring was characterized by an important parasitoid activity, while aphids remained at a low level. Later in spring, activity decreased, and aphid development began even during this period. During the summer, when aphids reached their population peak, parasitoid activity rose again. Percentage of parasitism of aphids sampled was only important during summer in red clover and rye-grass. In wheat and fallow grassland, percentage of parasitism remained at a low level. The role of synchronization between parasitoid activity and aphid development is discussed.

Emergence Pattern of Sorghum Midge and its Major Parasitoids on Midge-resistant and Susceptible Genotypes

Studies were conducted on the species composition of parasitoids of sorghum midge, Stenodiplosis sorghicola Coquillett (Diptera: Cecidomyiidae), emergence pattern and level of parasitism. They took place at the International Crops Research Institute for the Semi-Arid Tropics Asia Centre using three midge-resistant (ICSV 745, ICSV 89058 and IS 10712) and three susceptible (Swarna, CSH 9 and ICSV 112) genotypes during the 1992-93 post-rainy and 1993 rainy seasons. The species of parasitoids collected were Aprostocetus gala Walker, A. coimbatorensis Rohwer (Hymenoptera: Eulophidae) and Eupelmus spp. (Hymenoptera: Eupelmidae). The species composition varied with the season, but was unaffected by varietal resistance and susceptibility to the midge. Although both species of Aprostocetus were present in rainy and post-rainy seasons, A. gala was predominant during the rainy season whereas A. coimbatorensis was predominant in the post-rainy season. There was no significant difference in the pattern of parasitoid emergence or the level of midge parasitization between resistant and susceptible genotypes. These results indicate that resistance to midge in the genotypes studied was not antagonistic to parasitoid activity, and that there is potential to interface biological control with host-plant resistance in the management of this insect.

Integrated Management of Stemborers of Sorghum and Pearl Millet

Several species of stemborers attack sorghum and pearl millet in Africa and Asia. The commonest species on sorghum are Chilo partellus (Swinhoe) and Busseola fusca (Fuller) and on pearl millet, Contesta ignefusalis (Hampson). This paper discusses control options and the extent to which farmer perceptions of stemborers and associated crop losses have been considered. Examples of research aimed at developing IPM strategies are presented in the context of their impact or lack of it, on the farming community. Research efforts have traditionally focused on the development of resistant cultivare and only recently are they being targeted towards a combination with cultural and biological tactics. Conventional breeding procedures have not produced adequate levels of resistance to stemborers and natural enemies are not effective in regulating borer populations. The prospects of applied biological control and improved intercropping configurations are discussed. Reference is also made to progress in the role of semiochemicals in parasitoid activity on Ch. partellus and sex pheromones in the control of Con. ignefusalis. Unless resistance levels to stemborers are increased through biotechnological approaches, optimisation of the yield potential in existing cultivars requires that IPM research should focus on the improvement of cultural and biological components and should incorporate farmers' perceptions and an assessment of traditional pest management practices.

Effects of honeydew and insecticide residues on the distribution of foraging aphid parasitoids under glasshouse and field conditions

AbstractThe opposing effects of attraction to host‐derived kairomones and repellency from the pyrethroid insecticide deltamethrin were investigated with aphid parasitoids from the genus Aphidius (Hymenoptera: Aphidiinae). The spatial distribution of female parasitoids was recorded in a series of experiments conducted in a small glasshouse containing wheat plants either infested with cereal aphids, Sitobion avenae (F.) (Homoptera: Aphididae), uninfested or treated with the recommended field concentration of deltamethrin. The number of parasitoids per plant were counted at 0.5 h, 1 h and then at one hourly intervals up to 8 h after release. Parasitoids showed a strong aggregation response to aphid‐infested plants compared to adjacent uninfested plants. With the introduction of insecticide‐treated plants around the aphid‐infested plants, parasitoids showed a greater tendency to disperse away, resulting in fewer parasitoids on plants and significantly lower rates of aphid parasitism. The degree of aphid fall‐off from plants was a good indicator of parasitoid foraging activity. In field studies, using sticky traps to measure the activity of parasitoids in plots sprayed with water, deltamethrin and/or an artificial honeydew solution, repellent properties were evident for up to 2 days after application. The attraction/arrestment stimuli associated with the honeydew solution were sufficient for parasitoids to continue searching insecticide‐treated areas. The implications of these findings for parasitoids searching crops contaminated with aphid‐derived kairomones and insecticides are discussed.

SYNCHRONY BETWEEN POPULATIONS OF THE TARNISHED PLANT BUG, LYGUS LINEOLARIS (PALISOT DE BEAUVOIS) (HEMIPTERA: MIRIDAE), AND ITS EGG PARASITOIDS IN SOUTHWESTERN QUEBEC

AbstractThe seasonal occurrence of four species of egg parasitoids of the tarnished plant bug (Lygus lineolaris) was determined in three different habitais: fields of mixed weeds. alfalfa (Medicago sativa L.). and crown vetch (Coronilla varia L.) in southwestern Quebec in 1991 and 1992. Parasitoids studied were the mymarids Anaphes iole Girault, Polynema pratensiphagum (Walley), and Erythmelus miridiphagus Dozier and a scelionid, Telenomus sp. Adult populations of these parasitoids showed three or four population peaks in all habitats throughout the season. Adult parasitoid activity started during the first egg-laying period of L. lineolaris at a temperature accumulation of 73 degree-days (DD). The overwintering period began in mid-October at 1277 and 1058 DD for 1991 and 1992, respectively. All the parasitoids had a strong synchrony with L. lineolaris populations; specifically, marked peaks in the adult population of all species were in synchrony with the egg-laying periods of L. lineolaris.

Parasitoids (Hymenoptera: Pteromalidae, Ichneumonidae) of Filth Fly (Diptera: Muscidae) Pupae at Dairies in Alberta

Filth fly pupal parasitoids were surveyed for 2 yr at four dairies in southern Alberta. Seven parasitoid species were recovered. Muscidifurax raptor Girault & Sanders, M. zaraptor Kogan & Legner, and Trichomalopsis sp. were the most abundant and were recovered in both years. Other species were Urolepis rufipes (Ashmead), Phygadeuon sp. Spalangia cameroni Perkins, and Dibrachys cavus (Walker). Parasitism of intact pupae was generally <2%, but exceeded 30% on one occasion. Parasitoids were active from May to October, with most activity during August. Seasonal patterns for M. raptor and Trichomalopsis sp. were not consistent both years and were probably influenced by excessive rainfall during June 1991 and relatively low levels of parasitism. Parasitoid activity increased with increasing temperature and was negligible at temperatures below 11 degrees C.

Control of European corn borer in sweet corn by Trichogramma brassicae Bezd. (Hym., Trichogrammatidae)

AbstractThe biological control effectiveness of the indigenous egg parasitoid Trichogramma brassicae Bezd, reared continuously on Ostrinia nubilalis (Hb.) (ECB) eggs, was tested against ECB in sweet corn in 1991 (2 ha release plot) and 1992 (3.5 ha release plot). T. brassicae was reared for three‐four generations on the factidious host Ephestia kuehniella Zell. and then released on the crop; a 0.5 ha plot situated at 300–400m from the test plots was used as control in both years. Four releases, each totalling 250–300 000 individuals, were made the first year and three at the same rate per ha the second. ECB adult emergence was monitored using traps baited with sex pheromone and phenylacetaldehyde food attractant. The parasitoid activity was monitored via sentinel egg masses following each release. The parasitization rates of the sentinel egg masses was always higher in the release plot vs. control. The parasitization of natural egg masses sampled in both years before harvest was: 12.5 and 10.86% in control as against 87.5 and 68.58% in T. brassicae plots in the respective years. ECB damage was calculated on crop ear samples. The rate (%) of sentinel egg mass predation by wild predators showed no significant difference between control and release plots for both years. The low level of ECB damage to crop ears evinced the good search capacity, parasitization and control effectiveness of T. brassicae.

Use of trap plants as a means of measuring the activity of cereal aphid parasitoids in the field

The activity of cereal aphid parasitoids in the southern half of the New South Wales wheat belt was assessed by exposing potted barley seedlings infested with Rhopalosiphum padi at selected sites for about 12 days in autumn and again in spring, 1991. Two parasitoid species, Aphidius colemani and Aphidius similis were recovered at three out of 20 sites in autumn (May), and at 15 of 19 sites in spring (September). The level of parasitism varied considerably and exceeded 40% in individual pots at five sites in spring.

Induction of dormancy in aphid parasitoids: implications for enhancing their field effectiveness

The aphid parasitoid Pauesia unilachni Gahan entered diapause even under short night conditions at 20°C in oviparae of Schizolachnus pineti F. on Pinus sylvestris L., but Praon volucre Hal. did not under the same conditions in oviparae of Acyrthosiphon pisum Harris. Praon volucre or Aphidius matricariae Hal. reared in anholocyclic strains of Aulacorthum solani Kalt., Aphis gossypii Glover and Myzus ascalonius Doncaster did not enter diapause under long night conditions at 15°C. A cold shock could induce hibernal quiescence and diapause of Praon volucre in Acyrthosiphon pisum, but only hibernal quiescence occurred in this parasitoid developing in anholocyclic hosts. These observations show that environmental cues (temperature and photoperiod) as well as internal factors via host aphid such as host aphid life cycle, aphid morph and host plant quality are involved in the induction of dormant stages in aphid parasitoids. The importance of these findings is discussed in terms of enhancing parasitoid activity in the field.

Top‐Down Effects in a Tritrophic System: Parasitoids Enhance Plant Fitness

We determined the direct and indirect top—down forces in a tritrophic system composed of a guild of three parasitoid species (Necremnus tidius, N. folia, and Aprostocestus sp.), a single weevil seed—predator species (Ceutorhynchus sp. nov.), and the host plant, Hormathophylla spinosa, a woody crucifer of the high—mountain elevations of the Sierra Nevada (southeast Spain). By Means of observational and experimental approaches, we focused on the possible regulatory effects of parasitoids on the weevil population as well as on the analysis of the sign and strength of the resulting indirect effects on plant fitness. Weevill attacks 21.7% of the fruit produced by H. spinosa during the study, selecting fruits having the most seeds. Seeds eaten by weevils were significantly bigger than uneaten ones. The number of seeds per fruit after being depredated by Ceutorhynchus was significantly smaller than for fruit not attacked. Thus, weevils affect the fitness of the host plant both by decreasing the number of seeds (quantitative effect) and by reducing the average size of surviving seeds per fruit (qualitative effect). When parasitoids were excluded experimentally, the percentage of attacked fruit (which corresponds to the number of weevil larvae) rose from 20 to 43%. We assume that the increase in the experimental weevil population may be because excluding parasitoids eliminates not only death by parasitoid oviposition for some Ceutorhynchus larvae, but also death by direct predation of parasitoids on weevil larvae. We have also experimentally verified that parasitoid activity benefits the entire plant, by way of parasitoids contributing to a higher average number of seeds dispersed per fruit in each plant, by influencing both the abundance of the weevis and the behavior of the weevil larvae.

Within-Tree Distribution of Phyllonorycter blancardella (F.) and P. crataegella (Clemens) (Lepidoptera: Gracillariidae) and Associated Levels of Parasitism in Commercial Apple Orchards

The within-tree distribution of Phyllonorycter blancardella (F.) and P. crataegella (Clemens) and the associated levels of parasitism in commercial apple orchards were examined for 2 years at two sites in west-central Missouri. Canopies of 10 trees at both sites were divided into three regions (or heights): upper, middle, and lower. Each region was further divided into within-row and between-row positions. Leaf and mine samples were taken at the end of every leafminer generation to determine mean leafminer density (mines/leaf) and percent parasitism. Neither the leafminers nor the parasitoids displayed a preference for either the within-row or between-row canopy positions of the tree. However, at both sites and years, the mean level of mines/leaf was generally greater in the lower-middle canopy regions of the tree. Conversely, parasitoid activity appeared to be more evenly distributed throughout the tree with a tendency for higher levels of parasitism to be found in the middle-upper canopy regions. Early-season monitoring of leafminer and parasitoid activity can be accurately determined with leaf samples gathered from the lower portion of the canopy.

Seasonal Incidence of Diamondback Moth, Plutella xylostella L. and its Parasi Toids in Nilgiris

In Nilgiris, the larval population of diamond backmoth Plutella xylostella L. in cabbage was more from December to May with its peak activity during April. Diadegma semiclausm (Horstmann) and Cotesia plutellae (Kurdjumov) are widely established larval parasitoids. Activity of D.semiclasm was more during September. Level of parasitism by D.semiclausm was not influenced much by weather elements and host density. The parasitism by C. plutellae was more in hot-weather period and parasitoid activity was influenced by host density. Maximum temperature, and morning relative humidity had positive influence whereas, evening relative humidity had negative influence on C. plutellae p

Dormant-Season Sprays Affect the Mortality of Peach Twig Borer (Lepidoptera: Gelechiidae) and Its Parasitoids

The effectiveness of a dormant-season oil spray with or without an organo-phosphate insecticide for control of the peach twig borer, Anarsia lineatella Zeller, was investigated. Results from experimental field plots indicated that an application of a dormant oil alone resulted in poor control of peach twig borer inside the hibernaculum. Limb crotches containing live peach twig borer in hibernacula were field-collected and treated in the laboratory with either organophosphate (diazinon) and oil insecticides or varying concentrations of a dormant oil alone. Significantly greater larval mortality was found in the organophosphate treatment, whereas mortality in the oil treatments was not significantly different from the control. Overwintering larvae from an insectary colony that were exposed to two rates of an oil had significantly greater mortality than larvae in a control sprayed with water, indicating that peach twig borer inside the hibernaculum may be protected from the insecticidal activity of the oil. To determine the effect of dormant sprays on parasite species composition and numbers, peach twig borer were field-collected and reared through to adult moths or parasitoids. Parasitoid activity was low, with only 0.79% of peach twig borer parasitized (n = 3,032). Macrocentrus ancylivorus Rowher, Spilochalcis n.sp. aff torvina (Cresson), Paralitomastix pyralidis (Ashmead), Erynnia tortricis (Coquillett), Euderus cushmani Crawford, and an unidentified braconid species were reared from 2,528 peach twig borer collected in orchards that did not receive an organophosphate insecticide. A single parasitoid, M. ancylivorus , was reared from 504 peach twig borer collected in orchards treated with an organophosphate insecticide. The virtual absence of peach twig borer parasitoids in fields treated with an organophosphate may be a reflection of the low number of moth pests collected at those sites.

Relative and Seasonal Abundance of Beneficial Arthropods in Centipede grass as Influenced by Management Practices

Pitfall traps were used to monitor the seasonal activity of arthropod predators, parasitoids, and decomposers in replicated plots of centipedegrass turf for 3 yr (1989-1991) at two locations. During 1990 and 1991, the influence of single or combined herbicide, insecticide, and fertilizer applications on these beneficials was assessed. In total, 21 species of carabids in 13 genera and 17 species of staphylinids in 14 genera were represented in pitfall-trap collections. Nonsminthurid collembolans, ants, spiders, and parasitic Hymenoptera were adversely affected in the short term by insecticide applications targeting the twolined spittlebug, Prosapia bicincta (Say). Other taxa, notably oribatid Acari, increased over time in response to pesticide or fertilizer applications. Although various taxa were reduced by pesticide application during three of four sample intervals, a lack of overall differences in season totals suggests that the disruptive influence of certain chemical management practices may be less severe than expected in the landscape.

Biological Control of Citrus Blackfly (Homoptera: Aleyrodidae) in Nicaragua

A series of life tables based on field observations of mortality of citrus blackfly, Aleurocanthus woglumi Ashby, in a commercial orchard in Leon, Nicaragua (1986–1989), indicate that the solitary endoparasitoid Encarsia opulenta (Silvestri) is an important factor in the observed declines of outbreak citrus blackfly populations in 1986 and 1987. Parasitization by E. opulenta was disrupted by intensive rainfall and subsequent pesticide applications in the orchard but was restored when insecticide use was eliminated or dry weather conditions resumed. By mid-1988, survival of immatures to the adult stage was below theoretical replacement levels necessary for population increase, and populations declined to low, subeconomic densities. In late October 1988, heavy wind and rain of Hurricane Joan disrupted parasitoid activity and created conditions for potential outbreak adult citrus blackfly survivorship. E. opulenta reexerted control of the population to low-density subreplacement levels within the following four host generations.

Tritrophic relationships of Russian wheat aphid (Homoptera: Aphididae), a hymenopterous parasitoid (Diaeretiella rapae McIntosh), and resistant and susceptible small grains

The tritrophic relationships between resistant small grain entries, Russian wheat aphid, Diuraphis noxia (Mordvilko), and Diaeretiella rapae McIntosh were studied. Resistant triticale entries with high levels of antibiosis affected growth and reproduction of both the aphid and the parasitoid. Parasitoid mummies from antibiotic triticale were smaller, took longer to develop, and were fewer in number compared with those from susceptible entries. The sex ratio of parasitoids emerging from the smaller mummies of aphids restricted to the resistant triticale entries was skewed toward females. The protective influence of parasitoids on plants was demonstrated in the experiment. Plants exposed to aphids without parasitoids sustained greater damage and had significantly less biomass than those so protected. A resistant wheat entry showed a reduction in aphid populations and enhanced parasitoid activity due to the fact that its leaves did not roll like those in the susceptible wheat entry.