Development of Encarsia bimaculata (Heraty and Polaszek) (Hymenoptera: Aphelinidae) in Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) nymphs

Encarsia bimaculata was recently described from India as a potentially useful parasitoid of Bemisia tabaci. Its developmental biology was studied in the laboratory at 25–30 °C and 70–75% RH. Results showed that E. bimaculata is a solitary, arrhenotokous, heteronomous, autoparasitoid. Mated females laid eggs internally in B. tabaci nymphs that developed as primary parasitoids. Males developed as hyperparasitoids, either in females of their own species or in other primary aphelinid parasitoids. Superparasitism was common under cage conditions. Both sexes have an egg, three larval instars, prepupal, and pupal stages. Development from egg to adult took 12.70 ± 2.10 days for females and 14.48 ± 2.60 days for males. Individual B. tabaci nymphs were examined for E. bimaculata parasitization using three isozymes: esterase, malate dehydrogenase, and xanthine dehydrogenase. All three isozymes showed differential banding patterns that identified E. bimaculata parasitized or unparasitized B. tabaci nymphs.     

Intraguild predation on Eretmocerus sp. nr. emiratus,a parasitoid of Bemisia tabaci,by three generalist predators with implications for estimating the level and impact of parasitism

Intraguild predation (IGP) is pervasive in many managed and unmanaged ecosystems and may have negative, neutral or positive effects on the biological control of pest insects. Both generalist predators and aphelinid parasitoids attack Bemisia tabaci (Gennadius) Biotype B (=B. argentifolii Perring & Bellows) on cotton in the southwestern USA. Free-choice and no-choice laboratory assays were conducted to quantify prey consumption patterns and preference by three representative generalist predators, Geocoris punctipes (Say), Orius insidiosus (Say), and Hippodamia convergens Guérin-Méneville, offered fourth instar B. tabaci nymphs and nymphs parasitized by Eretmocerus sp. nr. emiratus. All three predators showed a significant preference for larval and pupal stage parasitoids over early fourth instar nymphs, but G. punctipes and O. insidiosus were non-discriminating when offered a choice of larval parasitoids and late fourth instar nymphs. The potential implications of these observed patterns for the field were examined through sensitivity analyses of existing field life table data. First, preference for parasitized hosts alters the methods required for calculating marginal rates of parasitism. Incorporating a preference variable in the estimation procedure had a very small positive effect (0.02–1.13% change) on total generational mortalities observed in previous life table studies. However, further hypothetical analyses suggested that under circumstances of lower generational mortality and higher levels of either apparent parasitism or predation, high levels of predator preference for parasitized prey could alter estimates of total mortality as much as 14%. Second, although intraguild predation was demonstrated, the implications for biological control are unclear. Based on field life table data the rate of IGP ranged from 0.019 to 0.126 depending on predator species and prey comparison, but accounting for these levels of IGP had only small negative effects on total generational mortalities (0.193–1.278% change).     

Host suitability of different instars of the whitefly Bemisia tabaci `biotype Q' for Eretmocerus mundus

Eretmocerus mundus Mercet is a parasitoidof Bemisia tabaci (Genn.) indigenous tothe Mediterranean and is used commercially foraugmentative biological control in Spain andelsewhere. A better understanding of thesuitability of different host instars wouldhelp optimize production and field application.Incidence of parasitism, development time,survivorship and sex ratio were evaluated whendifferent nymphal instars of the sweetpotatowhitefly Bemisia tabaci biotype `Q' wereoffered for parasitization. Experiments wereconducted on sweet pepper at 25 °C, 75%RH and 16:8 (L:D) photoperiod. E. mundusoviposited in all nymphal instars of B.tabaci except the mature 4th instar orpharate adult (previously designated, `pupa').Incidence of parasitism was greatest (33.8± 5.1 parasitized nymphs) and developmenttime shortest (14.1 ± 0.1 d) whenoviposition occurred under 2nd and3rd instar nymphs compared to 1st or4th instars. Survivorship (85%) andoffspring sex ratio (39.8% female) did notdiffer statistically for parasitoids developingin whiteflies that were parasitized asdifferent instars. Although 2nd and3rd instars were clearly the mostfavorable host stage for E. mundus, itscapacity to parasitize and develop on a widerange of host stages is a favorablecharacteristic for both rearing and fieldapplication.     

Mortality factors affecting Bemisia tabaci populations on cotton in Turkey

Cohort‐based, partial life tables were constructed to determine the sources and rates of mortality factors affecting Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) on cotton in the eastern Mediterranean region of Turkey over a two year period. Mortality factors were recorded as due to predation, parasitism, dislodgement and unknown for five developmental stages. Across 10 independent cohorts, the highest median rate of marginal mortality pooled over all stages was attributed to parasitism (0.69) followed by predation (0.67). The key factor was hypothesized to be parasitism based on graphical and regression‐based comparison of individual factor k‐values to total generational mortality. The greatest amount of marginal immature mortality occurred during the fourth nymphal stadium (median = 0.77) and mortality during this stage was also most predictive of variation in total mortality. Pooled over all developmental stages, the highest rates of irreplaceable mortality were associated with parasitism (median: 0.112), followed by predation (0.088), dislodgement (0.020) and unknown (0.017). Although crawler mortality was not explicitly measured, sensitivity analyses indicated that mortality during this stage would have changed total mortality by only 0.45–1.21% and had no effect on identification of key factors. There was no significant effect of cotton cultivar on any mortality factor or total mortality over the two years of study. Results suggest that conservation of natural enemies, particularly parasitoids, may provide for more sustainable management of B. tabaci on cotton in Turkey.     

Host-feeding of three parasitoid species on Bemisia tabaci biotype B and implications for whitefly biological control

Parasitoids in the genera Encarsia and Eretmocerus (Hymenoptera: Aphelinidae) are important biological control agents of whiteflies through their reproductive as well as host‐feeding activities. The feeding capacities of female parasitoids of three species with different reproductive strategies [Encarsia sophia (Girault & Dodd), Encarsia formosa Gahan, and Eretmocerus melanoscutus Zolnerowich & Rose] on their host, sweetpotato whitefly, Bemisia tabaci (Gennadius) biotype B (Homoptera: Aleyrodidae), were evaluated on cabbage in a single‐instar no‐choice experiment in the laboratory and a mixed‐instar choice experiment in the greenhouse. In both single‐ and mixed‐instar experiments, significant differences in host‐feeding capacities were found among the three parasitoid species. Encarsia sophia exhibited superior capacity of host‐feeding compared to E. formosa and E. melanoscutus. In the single‐instar experiment, parasitoids fed more on younger (smaller) hosts than older (larger) hosts. In the mixed‐instar experiments, all three parasitoid species exhibited a clear preference for feeding on older hosts compared to younger hosts. Total number of whitefly nymphs fed on by E. sophia was approximately three times that of the other two parasitoid species. Whitefly mortality accounted for by host‐feeding by E. sophia was up to 59.7%, and, thus, equivalent to parasitization. The significance of host‐feeding of E. sophia for biological control of B. tabaci is discussed.     

Strategy for orchard use of Bacillus thuringiensis while minimizing impact on Choristoneura rosaceana parasitoids

Trials were conducted to study how spring Bacillus thuringiensis Berliner subsp. kurstaki treatments on apple may be timed to maximize the survival of parasitoids of the obliquebanded leafroller, Choristoneura rosaceana (Harris) (Lepidoptera: Tortricidae), found in the southern interior of British Columbia, Canada. Orchard collections verified that second through fourth instar obliquebanded leafrollers were found in varying proportions from pink through the petal fall stage of apple development when spring B. thuringiensis treatments are applied vs. lepidopteran pests. Laboratory‐reared second through fourth instar obliquebanded leafrollers, unparasitized and parasitized by one of three native parasitoid species, were fed untreated apple leaves or leaves treated with B. thuringiensis. The highest mortality of unparasitized obliquebanded leafrollers occurred when fourth instars were exposed to B. thuringiensis‐treated leaves; B. thuringiensis‐induced mortality in the unparasitized second and third instars was less than 50%. The consumption of B. thuringiensis‐treated leaves by host larvae significantly increased the percentage of dead host larvae in all parasitized and unparasitized treatments. However, because of the low susceptibility of this leafroller species to B. thuringiensis, relatively high numbers (38–43%) of three obliquebanded leafroller parasitoid species were able to survive the consumption of B. thuringiensis by second and third instar host larvae. Fourth instar obliquebanded leafrollers were found at the full bloom and petal fall stage of apple development in the orchard, at which time B. thuringiensis treatments are recommended for optimal leafroller control. The highest parasitoid mortality due to host mortality was recorded in Apophua simplicipes Cresson (Hymenoptera: Ichneumonidae) and Macrocentrus linearis (Nees) (Hymenoptera: Braconidae), when the hosts were treated as fourth instars. Both of these parasitoids emerge from fifth and sixth instar obliquebanded leafrollers. Bacillus thuringiensis did not have as negative an impact on Apanteles polychrosidis Viereck (Hymenoptera: Braconidae), which emerges when the host is in the fourth instar. When leafroller mortality and parasitism were combined, the B. thuringiensis treatment did not significantly increase host elimination above that of parasitism alone, except for larvae parasitized by A. simplicipes that were in the fourth instar. The consumption of B. thuringiensis by unparasitized larvae was shown to slow larval development.     

Fitness of Encarsia sophia (Hymenoptera: Aphelinidae) parasitizing Trialeurodes vaporariorum and Bemisia tabaci (Hemiptera: Aleyrodidae)

Abstract Fitness and efficacy of Encarsia sophia (Girault & Dodd) (Hymenoptera: Aphelinidae) as a biological control agent was compared on two species of whitefly (Hemiptera: Aleyrodidae) hosts, the relatively smaller sweetpotato whitefly, Bemisia tabaci (Gennadius) biotype ‘B’, and the larger greenhouse whitefly, Trialeurodes vaporariorum (Westwood). Significant differences were observed on green bean (Phaseolus vulgaris L.) in the laboratory at 27 ± 2°C, 55%± 5% RH, and a photoperiod of 14: 10 h (L: D). Adult parasitoids emerging from T. vaporariorum were larger than those emerging from B. tabaci, and almost all biological parameters of E. sophia parasitizing the larger host species were superior except for the developmental times of the parasitoids that were similar when parasitizing the two host species. Furthermore, parasitoids emerging from T. vaporariorum parasitized more of these hosts than did parasitoids emerging from B. tabaci. We conclude that E. sophia reared from larger hosts had better fitness than from smaller hosts. Those from either host also preferred the larger host for oviposition but were just as effective on smaller hosts. Therefore, larger hosts tended to produce better parasitoids than smaller hosts.     

The biology of two Eretmocerus spp. (Haldeman) and three Encarsia spp. Forster and their potential as biological control agents of Bemisia tabaci biotype B in Australia

The performance, as measured by daily rate of parasitism and total parasitism, of five aphelinid species found in Australia parasitising Bemisia tabaci were compared on cotton, hibiscus, rockmelon, soybean and tomato. Two Eretmocerusspp., both indigenous to Australia, gave the highest levels of parasitism on each of the plant host species tested. The tritrophic interactions between B. tabaci, host plant species and Eret. mundus(Australian parthenogenetic form) (APF) were also examined. In general, more whiteflies were parasitised when cotton was the source host or rockmelon the test host. Parasitism was always low when tomato was either the source or test host. When parasitoids were transferred from rockmelon to cotton, parasitism declined. In contrast, parasitism increased when parasitoids were transferred from cotton to rockmelon. Parasitism also increased when parasitoids were transferred from soybean to rockmelon, yet failed to do so when shifted from soybean to cotton despite cotton normally being a better host. However, when parasitoids were transferred from cotton to soybean there was a marked increase in parasitism. Possible causes are discussed. The field cage trial demonstrated that parasitism by both Eretmocerus spp. increased with increasing whitefly density. Further, the increase in parasitism was not due to the presence of more parasitoids as neither the parasitoid-whitefly ratio nor the total number of parasitoids present had a significant effect on parasitism. The combination of the two species, gave similar levels of parasitism to that achieved by Eret. mundus(APF) alone. Subsequent identification of the emerged individuals indicated that over 50% of the parasitism was due to this species suggesting that it out-competed Eret. queenslandensis. Despite this competition, there was no evidence that overall control was compromised.     

Intraguild predation by the generalist predator Orius majusculus on the parasitoid Encarsia formosa

Intraguild predation of Orius majusculus (Reuter) (Heteroptera: Anthocoridae) on Encarsia formosa (Gahan) (Hymenoptera: Aphelinidae), both natural enemies of Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae), was studied under laboratory conditions. The experiments quantified prey consumption by 5th instar nymphs and adults of O. majusculus offered unparasitised 3rd, early 4th or 4th instar B. tabaci nymphs or parasitised nymphs containing 2nd or 3rd larval instar or pupal parasitoids. In addition, prey preference of the two stages of O. majusculus for parasitised or unparasitised whitefly nymphs was studied using nine different prey combinations. Both predator stages readily preyed upon on both unparasitised and parasitised B. tabaci. In no-choice experiments, predation on 3rd instar E. formosa by adult predators was the highest, while predator nymphs preyed most on unparasitised 3rd instar B. tabaci and 2nd instar parasitoids. Predation of predator stages was lowest on 4th instar B. tabaci and E. formosa pupae. In all prey combinations, both stages of O. majusculus showed a significant preference for parasitised over unparasitised whitefly nymphs except for the combination of 5th instars of O. majusculus with early 4th instar whiteflies and E. formosa pupae. The results indicate that intraguild interactions between O. majusculus and E. formosa may have negative effects on biological control of B. tabaci.     

Seasonal phenology and stage-specific parasitism of the apple ermine moth, Yponomeuta malinellus Zeller, in Korea

The apple ermine moth, Yponomeuta malinellus Zeller (Lepidoptera: Yponomeutidae), is a tent caterpillar that feeds on Malus spp. in Korea. Populations of the moth in native areas appeared to be regulated by the assemblage of parasitoids. Phenological associations between host stages and parasitoids, susceptible stage(s) of the host for each parasitoid, and stage‐specific parasitism were studied. The egg larval parasitoid Ageniaspis fuscicollis (Dalman) had highest parasitism of first instar larvae (24%), with 14% parasitism of other larval stages. Dolichogenidea delecta (Haliday) was recovered from all larval instars with the highest parasitism rate of second instar larvae (20.1%), followed by 19.9% parasitism of mid‐larval hosts. Herpestomus brunicornis Gravenhorst was reared from second instar larvae through to pupal collection, and had the highest parasitism rate (29.9%) at the pupal stage. The larval pupal parasitoid Zenillia dolosa (Meigen) was recovered from mid‐larval to pupal stages with the highest parasitism rate (5.5%) occurring in third to fourth instar larvae. The host stages for developing A. fuscicollis completely overlap with those of D. delecta, and with those of H. brunicornis to some degree. A statistically significant negative correlation exists between A. fuscicollis and these dominant parasitoids, indicating competitive interaction within the host.     

Food-deprived host-feeding parasitoids kill more pest insects

Some parasitoids not only parasitize their hosts but also destructively feed on them which could result in host mortality. We hypothesized that host-feeding parasitoids that are food-deprived before being released for biological control would destructively feed on more hosts, and an optimal duration of food deprivation of parasitoids would enhance host feeding without negatively affecting parasitism. We investigated the effects of food-deprivation durations (0, 3, 6, 10, 24 h and 20% honey solution offered), before being released, on the host mortality and parasitism by a destructive host-feeding parasitoid of whitefly nymphs, Encarsia sophia (Girault & Dodd) (Hymenoptera: Aphelinidae). In another experiment, we compared host feeding, parasitization and longevity throughout the lifespan between food-deprived and non-food-deprived parasitoids. Using fourth-instar Bemisia tabaci B biotype as the host, the responses of E. sophia differed significantly with the durations of food deprivation before they were exposed to their hosts. E. sophia adults food-deprived for 6 h killed more hosts through feeding than those that were food-deprived for 0, 3, 10 and 24 h or those that were fed with honey solution. Moreover, parasitoids that were food-deprived for 6 h parasitized more hosts than those held for other durations of food deprivation. Similar results on host-feeding were found when third-instar whitefly nymphs were used. We confirmed that E. sophia food-deprived for 6 h not only killed more whiteflies through host feeding, but also lived significantly longer and parasitized more hosts than the non-food-deprived ones throughout their lifespan. Our results could be extended to improve the effectiveness of augmentative biological control of pests through improved host feeding and parasitizing capacity by starving the parasitoids for a certain period of time before they will be used.     

Bemisia tabaci (Homoptera: Aleyrodidae) instar effects on rate of parasitism by Eretmocerus mundus and Encarsia pergandiella (Hymenoptera: Aphelinidae)

Studies were conducted to compare preference among Bemisia tabaci Gennadius, biotype B instars for parasitization by Eretmocerus mundus Mercet and Encarsia pergandiella Howard when provided one instar only, two different instars, and four different instars simultaneously. In the single‐instar no choice treatment, Er. mundus was more successful in parasitizing the younger host instars, while En. pergandiella parasitized a greater proportion of the older instars. Similar results were observed when parasitoids were provided a choice of two instars in six different pair combinations. When all four instars were provided simultaneously, the numbers of first, second, and third instars parasitized by Er. mundus were not significantly different from each other (range 10.3–16.4%), but all were significantly higher than parasitism of fourth instar nymphs (2.1%). The highest percentage parasitization by En. pergandiella was in third instar (17.2%), and the lowest in first instar (2.8%).     

Parasitism,host feeding and immature development of Encarsia formosa reared from Trialeurodes vaporariorum and Bemisia tabaci on Trialeurodes ricini

Encarsia formosa Gahan (Hymenoptera: Aphelinidae), a thelytokous parasitoid, is an important biological control agent of whiteflies because of its outstanding reproduction and host‐feeding ability. In this study, we evaluated the parasitism, host feeding and developmental time of E. formosa populations reared on Trialeurodes vaporariorum (Westwood) (EFT) or on Bemisia tabaci (Gennadius) (EFB) when different nymphal instars of the castor whitefly, Trialeurodes ricini (Misra), were offered as hosts, with an aim to understand the preference of the parasitoid on nymphal instars of T. ricini. Experiments were conducted on castor bean plants at 26 ± 2°C, 50–60% RH and 16 : 8 (L : D) photoperiod. The results showed that E. formosa successfully oviposited and fed on all nymphal instars of T. ricini. However, numbers of the first instars fed on by the E. formosa populations reared on T. vaporariorum (EFT) and B. tabaci (EFB) were significantly greater (45.9 and 31.3, respectively) than those of the second (EFT: 30.4 and EFB: 15.8), the third (EFT: 22.4 and EFB: 13.2) and the fourth nymphal instars (EFT: 6.0 and EFB: 3.8). The number of T. ricini nymphs parasitized by E. formosa varied significantly among different instars, and the parasitism rates on the first instar (EFT: 15.2; EFB: 7.7) and fourth instar (EFT: 19.3; EFB: 4.9) were greater than those on the second and third instars. Encarsia formosa reared on T. vaporariorum had a significantly higher host feeding and ovipositing potential on T. ricini than EFB. When parasitizing the fourth instar nymphs, E. formosa completed development in a significantly shorter time (12.9 day) than when ovipositing in other instars (17.8–19.1 day). These results showed that EFT had a better host adaption than EFB. The information from this study should be useful for us to better understand the performance and nymphal preference of E. formosa from T. vaporariorum and B. tabaci when they parasitized and fed on T. ricini, and the interactions of parasitoids with different host whitefly species.     

Functional response,host stage preference and interference of two whitefly parasitoids

The functional responses of two parasitoids, Eretmocerus hayati Zolnerowich & Rose and Encarsia sophia Girault & Dodd, of whitefly Bemisia tabaci Gennadius Middle East‐Asia Minor 1 were studied under laboratory conditions. In addition, the influence of host density and host stage on the competitive interactions between the two parasitoids, and biological control effect on whitefly were evaluated. In the functional response study, adult parasitoids were tested individually, with a conspecific or heterospecific competitor. Both Er. hayati and En. sophia exhibited a type II response to increasing host density, whether a conspecific or heterospecific competitor was present or not. Difference of searching rates and handling times between treatments suggested interference interactions existed between two parasitoid species. In the host stage preference study, two parasitoid species were jointly tested. Er. hayati had a competitive advantage over En. sophia when provided young host instars (first and second instar), whereas no advantage was found on old host instars (third and fourth instar). The biological control effect of Er. hayati and En. sophia in different introductions varied with host density. However, the effect of host instar on host mortality was not significant. These findings provide information for the practice of biological control and give better insight into how parasitoid species may coexist in diverse environments.     

Competitive Interactions between Parasitoids Provide New Insight into Host Suppression

Understanding the dynamics of potential inter- and intraspecific competition in parasitoid communities is crucial in the screening of efficient parasitoid species and for utilization of the best parasitoid species combinations. In this respect, the host-parasitoid systems, Bemisia tabaci and two parasitoids, Eretmocerus hayati (exotic) and Encarsia sophia (existing) were studied under laboratory conditions to investigate whether interference competition between the exotic and existing species occurs as well as the influence of potential interference competition on the suppression of the host B. tabaci. Studies on interspecific-, intraspecific- and self-interference competition in two parasitoid species were conducted under both rich and limited host resource conditions. Results showed that (1) both parasitoid species negatively affect the progeny production of the other under both rich and limited host resource conditions; (2) both parasitoid species interfered intraspecifically on conspecific parasitized hosts when the available hosts are scarce and; 3) the mortality of B. tabaci induced by parasitoids via parasitism, host-feeding or both parasitism and host-feeding together varied among treatments under different host resource conditions, but showed promise for optimizing control strategies. As a result of our current findings, we suggest a need to investigate the interactions between the two parasitoids on continuous generations.     

双斑恩蚜小蜂寄生对烟粉虱体内保幼激素和20-羟基蜕皮酮含量的影响

用反相高效液相色谱法（RP-HPLC）测定了烟粉虱Bemisia tabaci体内保幼激素和20-羟基蜕皮酮的滴度。结果显示,被双斑恩蚜小蜂Encarsia bimaculata寄生的烟粉虱高龄若虫体内的保幼激素滴度显著高于（P<0.05）对照即未被寄生的高龄若虫,20-羟基蜕皮酮（20-E）滴度显著低于（P<0.05）对照,与未被寄生的低龄若虫滴度差异不显著,说明双斑恩蚜小蜂寄生后可以将烟粉虱高龄若虫的激素含量保持在低龄若虫的水平,从而调节烟粉虱高龄若虫的生长发育。烟粉虱伪蛹和成虫与对照体内保幼激素含量,烟粉虱伪蛹与对照之间20-E含量差异均不显著（P>0.05）。     

Encarsia formosa parasitizing the Poinsettia-strain of the cotton whitefly,Bemisia tabaci, on Poinsettia: bionomics in relation to temperature

Adult longevity, developmental time and juvenile mortality ofEncarsia formosa Gahan (Hymenoptera:Aphelinidae) parasitizing the Poinsettia-strain ofBemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) on Poinsettia (Euphorbia pulcherrima Willd.) were investigated in laboratory experiments at three temperatures: 16 °C, 22 °C and 28 °C. Furthermore, the parasitoid's preference for different larval stages of the whitefly was determined at 24.5 °C. The lifespan ofE. formosa decreased with temperature from one month at 16 °C to nine days at 28 °C. A lower temperature threshold of 11 °C for adult development was found. The development of juvenile parasitoids inB. tabaci lasted more than two months at the lowest temperature, but was only 14 days when temperature was 28 °C. The lower temperature threshold for immature development was 13.3 °C, yielding an average of 207 day-degrees for the completion of development into adults. Juvenile mortality was high, varying from about 50% at 16 °C to about 30% at 22 °C and 28 °C.E. formosa preferred to oviposit in the 4th instar and prepupal stages ofB. tabaci followed by the 2nd and 3rd instars. The preference for the pupal stage was low. The parasitoid used all instars of the whitefly for hostfeeding, with no apparent differences between the stages. The average duration of the oviposition posture was four minutes. Demographic parameters were calculated from life tables constructed from the data. The intrinsic rate of increase (r _m) and the net reproductive rate (R ₀) increased with temperature from 0.0279 day⁻¹ at 16 °C to 0.2388 day⁻¹ at 28 °C and from about 12 at 16 °C to about 66 at 28 °C, respectively.     

Occurrence and activity of <Emphasis Type="Italic">Bemisia tabaci</Emphasis> parasitoids on cassava in different agro-ecologies in Uganda

Bemisia tabaci Gennadius (Homoptera: Aleyrodidae) is the vector of cassava mosaic geminiviruses that cause cassava mosaic disease (CMD), which in turn causes devastating yield losses. Surveys were conducted from October 2000 to November 2001 in four agro-ecologies in Uganda to enhance the understanding of parasitoid fauna and parasitism of B. tabaci in cassava fields. Such an understanding is an essential prerequisite for the development of biological control methods of B. tabaci to complement current CMD control practices. Parasitoid abundance and parasitism efficiency varied between locations and sampling dates within the locations; highest parasitoid densities were observed at Namulonge in the Lake Victoria crescent while the lowest was at Kalangala. In all locations, parasitism was mainly due to Encarsia sophia Dodd and Girault and Eretmocerus mundus Mercet (all Hymenoptera: Aphelinidae). Two occasionally observed species included Encarsia mineoi Viggiani (Hymenoptera: Aphelinidae), only observed at Namulonge, and blackhead Encarsia (Hymenoptera: Aphelinidae) observed at Bulisa, Namulonge and Lyantonde. Parasitism efficiency was highest at Bulisa (57.9%), but ranged from 40.2 to 46.9% at the other three sites. This paper discusses the possible causes of variations in parasitoid abundance and parasitism efficiency, and proposes further studies that might be carried out to assess the potential for augmentation of parasitoids to control B. tabacipopulations and CMD.     

Intraguild interactions between the predator Macrolophus pygmaeus and the parasitoid Eretmocerus mundus,natural enemies of Bemisia tabaci

The native parasitoid Eretmocerus mundus Mercet and the predator Macrolophus pygmaeus Rambur are widely used to control Bemisia tabaci (Gennadius) in Mediterranean tomato greenhouses. An optimal biological control strategy for B. tabaci should take into account intraguild interactions between these natural enemies. In this study, predator's prey preferences and prey consumption were studied when offered different parasitoid and whitefly stages. The effect of the host plant on the adults of both natural enemies was also examined. M. pygmaeus preferred to consume B. tabaci over E. mundus when immature stages and adults of B. tabaci and E. mundus were offered. They consumed a larger amount of healthy B. tabaci nymphs and adults than of parasitised nymphs or E. mundus adults. The predator M. pygmaeus interfered with the reproduction of E. mundus females on cotton but not on tomato. However, B. tabaci nymphal mortality on tomato associated with parasitoid host feeding was also lower when the adult parasitoids coexisted with the predators. The joint release of M. pygmaeus and E. mundus adults did not increase the control of the whitefly B. tabaci.     

Non-target parasitism of the endemic New Zealand red admiral butterfly (Bassaris gonerilla) by the introduced biological control agent Pteromalus puparum

The New Zealand red admiral butterfly, Bassaris gonerilla (F.) (Lepidoptera: Nymphalidae), has been known as a non-target host for the introduced biological control agent Pteromalus puparum (L.) (Hymenoptera: Pteromalidae) for at least 35 years, but the level of parasitism has never been quantified. Pre-imaginal mortality in B. gonerilla was assessed over the southern summer of 2000/01 at six field sites in the Christchurch area of the South Island, New Zealand. Individual eggs and larvae were identified by tagging the stem of the Urtica ferox Forst.f. plant on which they were found and the fate of these individuals was checked weekly. These data were used to construct a partial life table for B. gonerilla. Egg mortality was very high (95%), with parasitism by an unidentified Telenomus sp. Haliday (Hymenoptera: Scelionidae) causing 57% mortality. Mortality in the larval and pupal stages increased at a constant rate with age and the major mortality factor was disappearance, which was assumed to be a result of predation and dispersal of larvae. The introduced biological control agent P. puparum parasitized 14% of B. gonerilla pupae sampled. However, parasitism by another exotic parasitoid, the self-introduced Echthromorpha intricatoria (F.) (Hymenoptera: Ichneumonidae), was even higher at 26%. A survey of pupal parasitism in three regions of New Zealand (Wellington, Christchurch, and Dunedin) revealed overall parasitism levels of 67% by E. intricatoria and 8% by P. puparum, but due to the difference in emergence times of B. gonerilla and its parasitoids, these are likely to be overestimates of percent parasitism. It is concluded that P. puparum has permanently enhanced mortality in B. gonerilla, but the level of mortality is low relative to egg parasitism by Telenomus sp., larval disappearance mortality, and pupal mortality due to E. intricatoria parasitism. To determine if this level of pupal parasitism has had population effects will require more data and the development of a population model for B. gonerilla.