Quality and environmental factors affecting Trichogramma brassicae efficiency under field conditions

Field parasitism of the egg parasitoid Trichogramma brassicae Bezdenko (Hymenoptera, Trichogrammatidae) (synonymous to T. maidis Pint. et Voegele) on Ostrinia nubilalis Hübner was compared to four single quality parameters (walking speed, fecundity on the factitious host Ephestia keuhniella Zeller, fecundity on the natural host O. nubilalis, and life span) previously measured in the laboratory and, a quality index calculated from three of the measured parameters. A single quality parameter (fecundity on E. keuhniella) and the calculated quality index showed a correlation to T. brassicae field parasitism, for different T. brassicae populations. The number of female Trichogramma released clearly influenced parasitism but not in the same proportion for all populations tested, reflecting that numbers released can only to some extent compensate for low quality in Trichogramma. Variation indegree hours above 18°C also influenced field parasitism. When incorporating degree hours to the quality index a significant correlation R²=0.56 (P=0.01) is obtained. In this work fecundity of T. brassicae on E. keuhniella can be as good an indicator for the potential field performance of T. brassicae, as the quality index which takes into account three quality parameters. Since environmental factors can obscure the potential performance of a population, i.e., one which under optimal laboratory conditions performs well, the quality index gives only a partial indication of how the released strains will perform in the field.     

Host-foraging success of three species of Trichogramma (Hymenoptera: Trichogrammatidae) in a simulated retail environment

Three species of trichogrammatid egg parasitoids (Trichogramma deion Pinto & Oatman, Trichogramma ostriniae Pang & Chen, and Trichogramma pretiosum Riley) (Hymenoptera: Trichogrammatidae) were evaluated under laboratory conditions as potential biological control agents for the Indianmeal moth, Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae), on retail shelves. A single shelving unit was used in each trial and a grid of sentinel egg disks was used to evaluate foraging success. The shelving consisted of pallet units with five shelves that were either bare or stocked with empty cereal boxes. In each replicate, approximately 500 female Trichogramma were released at the center of the shelving unit and allowed to forage for 48 h. Percentage of egg parasitism and percentage of host egg mortality were recorded after 7 d. Foraging success as well as the spatial pattern of parasitism differed significantly among the three Trichogramma species. Percentage of egg parasitism was approximately 4 times greater for T. deion than for T. ostriniae or T. pretiosum. The vertical distribution of parasitism by T. deion was also more uniform than for the other two species. In addition, the presence of packaging affected the foraging efficiency of T. ostriniae and T. pretiosum but not T. deion. Based on these findings, Trichogramma deion may be the best-suited candidate for augmentative biological control of P. interpunctella in retail stores, and a central release point of T. deion will likely provide adequate coverage of products on pallet-type shelving.     

Laboratory Performance Predicts the Success of Field Releases in Inbred Lines of the Egg Parasitoid Trichogramma pretiosum (Hymenoptera: Trichogrammatidae)

In this study we assessed the relationship between the laboratory and field performance of different isofemale lines of Trichogramma pretiosum Riley. In comparative assays, we used three rare mitochondrial haplotypes as genetic markers of the isofemale lines, and by introgressing these mitochondrial haplotypes into each of 15 genetically different nuclear lines, also tested the assumption that mitochondria are neutral markers. In a laboratory trial, 45 isofemale lines (15 nuclear genotypes x three mitochondrial haplotypes) were ranked in three categories (best, intermediate and worst) according to the mean offspring production and the proportion of female offspring. Subsequently, lines from each of the three categories were selected for field releases to quantify field parasitism on Ephestia kuehniella. Temporally separate releases were done in a transgenic Bt cornfield, with four plots, each with 50 points of recapture. The points of recapture consisted of trap cards with eggs of E. kuehniella collected daily. The trap cards were maintained in the laboratory at 25°C until the adult wasps emerged, and the maternal identity of the wasps was determined using qPCR and high-resolution melt curve analysis to determine the mitochondrial haplotype. The results showed that these measures of laboratory performance (fecundity and offspring sex ratio) were good predictors of field success in T. pretiosum. We also report strong evidence discrediting the assumption that mitochondria are neutral, in view of the correlation between performance and mitochondrial haplotype.     

Influence of environmental conditions and parasitoid quality on field performance of Trichogramma minutum

The effects of weather conditions and two parasitoid quality attributes, realized fecundity and host acceptance, were assessed on the field efficacy of mass-released Trichogramma minutum. Temperature was the most important single variable, explaining up to 75% of the variation in field parasitism. There were significant positive relationships between both the sum of the maximum temperatures and the number of degree-hours above a 15 °C threshold, accumulated in the three days following the release, and parasitism in the field. There was a significant negative relationship between the mean relative humidity and the odds of parasitism in the field. Quality parameters based on parasitoid biology were not effective for predicting field efficacy if poor weather conditions persisted after a release. If weather conditions were good (i.e. accumulated maximum temperatures above 62 °C, in the 3 days following the release), then parameters such as release rate and fecundity in the lab were useful predictors of field performance. There was no relationship between host acceptance measured in the lab and field parasitism. Given the importance of field temperatures for field performance, selection for cold tolerance of T. minutum would be desirable.     

Use of tetracycline in larval diet to study the effect of Wolbachia on host fecundity and clarify taxonomic status of Trichogramma species in cured bisexual lines

Endosymbionts of the genus Wolbachia were efficiently cured from Trichogramma species by incorporating 0.02% tetracycline into the artificial diet used to rear larvae. Use of this technique yielded stable cured lines (bisexual and arrhenotokous lines) in which no Wolbachia organisms were detected by PCR for up to 14 generations after curing. Four cured strains of Trichogramma pretiosum showed a significantly lower total fecundity compared to their Wolbachia-infected counterpart. However, the fecundity of a single cured strain of Trichogramma evanescens was similar to its Wolbachia-infected counterpart. These differences in the effect on fecundity may be due to differences between the Wolbachia strains infecting T. pretiosum or T. evanescens, providing additional evidence for the hypothesis that a specific interaction exists between some Trichogramma species and their Wolbachia symbionts. Tetracycline in larval diet was also used to generate bisexual strains of Trichogramma oleae and Trichogramma cordubensis so that these species could be crossed with the closely related species, respectively, T. pretiosum and T. evanescens, to test their compatibility. These crosses showed a lack of compatibility, validating maintenance of these as distinct species.     

Measurement and Selection of Parasitoid Quality for Mass-Reared Trichogramma minutum Riley Used in Inundative Release

Parasitoid quality, subject to both genetic and environmental influences, is critical to the success of any biological control program, however, its measurement and improvement is poorly understood. In this study, a classic genetic approach is taken to develop two indices, namely a character index and a fitness index, for the measurement and selection of high quality parasitoids used in inundative release. Six life-history traits and corresponding fitness components in 33 inbred strains of Trichogramma minutum were used to generate both genotypic and phenotypic variance-covariance matrices that then allowed for the construction of the indices. Most traits and their fitness components were positively correlated, both phenotypically and genotypically, with lifetime fecundity and the number of female offspring appearing to have an important influence. Selection of the top three strains showed that parasitoid quality could be improved by 36% using the character index and possibly up to 150% using the fitness index. The two indices were linearly correlated suggesting that either could be used to measure quality. The character index is recommended because it requires information on only three life-history traits (fecundity, number of female offspring, and number of male offspring) and has highly correlated responses of fitness components. Our work demonstrates that the best quality T. minutum will be obtained by using the character index to select for inbred strains which have high fecundity and number of female offspring.     

First report of parasitism of the Trichogramma bruni Nagaraja (Hymenoptera: Trichogrammatidae) in eggs of urbanus proteus (L.) (Lepidoptera: Hesperiidae) in snap beans (Phaseolus vulgaris) ( L.)

Aiming to verify the presence of eggs parasitoids of the genus Trichogramma, for using in the biological control of insects pests, were collected eggs from long tailed skipper butterfly, a lepidopteran defoliator of snap beans, which presented eggs with parasitism characteristics (dark eggs). The eggs were taken to the laboratory were 44.9% of parasitism was verified. Viability was 96.3%, with an average of 6.6 individuals per egg and a sexual ratio of 0.93. Male specimens were identified as Trichogramma bruni Nagaraja. It is the first report of parasitism in this host and culture.     

Biological Control Potential of Wolbachia -infected Versus Uninfected Wasps: Laboratory and Greenhouse Evaluation of Trichogramma cordubensis and T. deion Strains

The effects of thelytoky-inducing Wolbachia ( &#102 -proteobacteria) on Trichogramma cordubensis and T. deion (Hymenoptera, Trichogrammatidae) were studied in laboratory and greenhouse conditions. One infected (thelytokous, all female) line of each wasp species was compared with its conspecific uninfected (arrhenotokous, sexual) counterpart for several fecundity and dispersal traits. Arrhenotokous lines had a higher fecundity than their thelytokous counterparts, which suggests that Wolbachia negatively affect the fecundity of Trichogramma females. The arrhenotokous females dispersed more in the laboratory than their thelytokous counterparts. In the greenhouse, the opposite effect or no difference between lines was found, indicating that the laboratory set-up used to measure dispersal is not useful to predict relative dispersal of the females in the greenhouse. Calculations show that by releasing 100 adult wasps of both lines, thus including arrhenotokous males in the sexual line, more eggs are parasitized by the thelytokous wasps. Therefore, in spite of their lower individual female fecundity, thelytokous lines have a better potential for biological control than their arrhenotokous counterparts.     

Comparative biology and life tables of Trichogramma evanescens and T. cacoeciae with Ephestia elutella as host at four constant temperatures

The age-specific fecundity of Trichogramma evanescens Westwood and T. cacoeciae Marchal (Hymenoptera: Trichogrammatidae) with Ephestia elutella (Hübner) (Lepidoptera: Pyralidae: Phycitinae) as host and the life span of the adults with and without hosts was determined at 20, 26, 30 and 35 °C and 75 ±5% r.h. in the laboratory. At 35 °C, no progeny emerged. The availability of hosts prolonged the longevity in both species. Longevity, percentage of parasitism, fecundity, and the intrinsic rate of natural increase were higher in T. evanescens than in T. cacoeciae. Trichogramma evanescens is expected to be more effective than T. cacoeciae for use in biological control of Ephestia spp., especially at low and high temperatures.     

Effects of cold storage on field and laboratory performance of Trichogramma carverae (Hymenoptera: Trichogrammatidae) and the response of three Trichogramma spp. (T. carverae, T. nr. brassicae, and T. funiculatum) to cold

Delaying emergence of Trichogramma spp. is critical for commercial production. Here, diapause induction was considered for three species (Trichogramma nr. brassicae Bezdenko, Trichogramma carverae Oatman & Pinto, and Trichogramma funiculatum Carver), and the effect of storage temperature (4 degrees C, 8 degrees C, and 10 degrees C) and time (1-8 wk) was investigated for T. carverae. For all species, percentage of emergence was lowered after an initial diapause induction period (28 d at 14 degrees C and a photoperiod of 8:16 [L:D] h) and lowered further after 1-mo storage at 3 degrees C and a photoperiod of 0:24 (L:D) h. No wasps emerged after 2 mo of storage, suggesting that true diapause was not induced. The effect of 1-8-wk storage on wasp quality was investigated for T. carverae both in the laboratory and the field. Initial fieldwork suggested that this species could be successfully stored at 10 degrees C under continuous light (after 5-d development at 25 degrees C and a photoperiod of 16:8 [L:D] h) without reducing the ability of wasps to parasitize eggs in the field. In a second experiment, storage temperatures lower than 10 degrees C and storage times 3 wk or longer had a negative impact on emergence and longevity, and effects were not additive. Negative effects may partly reflect size changes, because size decreased in response to storage time, and there was an interaction between time and temperature effects on size. Storage time was the major factor influencing fecundity and field success; both fitness measures were reduced after storage of 3 wk or longer. T. carverae can therefore be successfully stored for up to 2 wk without detrimental effects, and 10 degrees C is the preferred storage temperature. T. carverae seems to survive unfavorable temperature conditions by entering a state of quiescence.     

Trichogramma exiguum (Hymenoptera: Trichogrammatidae) releases in North Carolina cotton: evaluation of heliothine pest suppression

Field studies were conducted in 1996 and 1997 to reevaluate the use of augmentative releases of Trichogramma wasps for heliothine management in cotton. In 1996, nine releases of Trichogramma exiguum Pinto & Platner, spaced 3-4 d apart, were made into three 0.4-ha cotton plots. Six weekly releases were made in 1997, each containing two T. exiguum cohorts developmentally staggered by 45 degrees C degree-days. Field release rates, estimated from laboratory and field quality control data, averaged 108,357 T. exiguum female female per hectare per cohort per release in 1996 and 193,366 female female per hectare per cohort per release in 1997. In 1996, mean +/- SD adult emergence under laboratory conditions for released cohorts was 92 +/- 7%; 62 +/- 5% of emerged adults were females, 3 +/- 2% of females displayed brachyptery (nonfunctional wings), mean female longevity under laboratory conditions was 15 +/- 4 d, and mean +/- SD field emergence was 97 +/- 2%. Quality control measurements were similar in 1997. In 1996, mean +/- SD percent parasitism of heliothine eggs in field plots on the sampled dates ranged from 67 +/- 4 to 83 +/- 5% in T. exiguum release plots and 25 +/- 9 to 55 +/- 8% in control plots. In 1997, parasitism levels ranged from 74 +/- 4 to 89 +/- 5% in T. exiguum release plots and 18 +/- 18 to 69 +/- 11% in control plots. Despite increased parasitism levels in T. exiguum release plots, there were no significant differences in density of fifth instars, boll damage, or yield between T. exiguum release and control plots. Therefore, it is concluded that Trichogramma augmentation is not an effective heliothine management tool in North Carolina cotton.     

Effects of shelf architecture and parasitoid release height on biological control of Plodia interpunctella (Lepidoptera: Pyralidae) eggs by Trichogramma deion (Hymenoptera: Trichogrammatidae)

The effects of shelving type, packaging, and release height on success of Trichogramma deion Pinto & Oatman (Hymenoptera: Trichogrammatidae) parasitizing Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae) eggs was studied under laboratory conditions. In trials on multipletiered gondola-type or open shelving units, with or without packaging, foraging success was evaluated by comparing parasitism and total mortality rates of sentinel egg disks among shelves after a single point-release of T. deion. Results showed that T. deion parasitized more egg disks and killed more total eggs on open shelves than on gondola shelving. The presence of packaging had no effect on parasitoid foraging on open shelves; however, packaging did interfere with parasitism of P. interpunctella eggs on gondola shelving. Egg parasitism and mortality patterns among shelves were not as evenly distributed on gondola-type shelving compared with open shelving. On gondola shelves without packages, changing the release point of T. deion from the middle to the lowest shelf shifted the distribution of parasitism toward the floor. Gondola shelving, especially in the presence of packaging, reduced foraging efficiency of T. deion for P. interpunctella eggs. Thus, to attain adequate control of P. interpunctella, it may be necessary to use two release heights on gondola shelving.     

Effect of temperature on parasitism and host-feeding of Trichogramma turkestanica (Hymenoptera: Trichogrammatidae) on Ephestia kuehniella (Lepidoptera: Pyralidae)

The egg parasitoid Trichogramma turkestanica Meyer is being evaluated as a biological control agent against the Mediterranean flour moth, Ephestia kuehniella Zeller, in flour mills. The longevity, parasitism and host-feeding of the parasitoid at four constant temperatures (15-30 degrees C) has been determined in the laboratory. The highest fecundity occurred at intermediate temperatures. The number of host eggs killed by host-feeding per female was highest at the two lower temperatures. A very conservative estimate of host-feeding showed that it accounts for approximately half of the mortality of host eggs at 20 and 25 degrees C and thus could constitute a major mortality factor for the flour moth population.     

Flight activity assessment of the egg parasitoidTrichogramma brassicae (Hym.: Trichogrammatidae) in laboratory and field conditions

A laboratory and a field test for flight initiation ofTrichogramma brassicae Bezdenko (Hymenoptera, Trichogrammatidae) (synonymous toT. maidis Pintureau et Voegele) were developed with the aim to establish a simple, cheap and quick flight quality control method forTrichogramma producers. The flight quality of four strains ofT. brassicae reared onEphestia kuehniella Zeller eggs were compared. The material tested consisted of four strains: two strains reared for two (F2) and 39 to 42 (F39–42) generations onE. kuehniella eggs without storage treatment, a diapause strain reared six generations (F6) onE. kuehniella eggs and a commercial strain also reared onE. kuehniella eggs whose production and storage conditions were unknown. Clear differences in flight activity among strains were observed. Both, the F2 and commercial strain showed significantly better flight activity under laboratory conditions compared to the other strains. Flight field cage experiments were made for comparison between field and laboratory results. Similar differences among strains in field cage experiments were observed when compared to laboratory tests.     

Assessing European Egg Parasitoids as a Mean of Controlling the Invasive South American Tomato Pinworm Tuta absoluta

The South American tomato pinworm (Tuta absoluta) has recently invaded Europe and is rapidly spreading in the Afro-Eurasian continent where it is becoming a major pest on tomato crops. Laboratory tests were undertaken to evaluate the potential of 29 European strains of Trichogramma parasitoids to control T. absoluta. In addition to the host itself, the host plant (tomato) was used during the laboratory tests in order to increase the chance of selecting the best parasitoid strains. Trichogramma females were placed with T. absoluta eggs on a tomato leaflet in tubes. We compared the parasitism of T. absoluta by the various Trichogramma species tested to the Trichogramma species currently commercially available for the pest control in Europe, i.e. Trichogramma achaeae. Thereafter, the more promising strains were tested on a larger scale, in mesocosm (i.e. cages in greenhouses) and in greenhouse compartments to evaluate efficiency of laboratory selected strains under cropping conditions. The most efficient strain from the laboratory screening trials did not perform as efficiently under the greenhouse conditions. We discuss differences in parasitism levels among species and strains and among the different scales tested in the experiments, as well as implications of these results for further screening for biocontrol agents.     

In Vitro Development of Trichogramma spp. (Hymenoptera: Trichogrammatidae) in Long-term Stored, Freeze-dried Artificial Media

Freeze-dried media were successfully used to facilitate the rearing of oophagous parasitoids of the Trichogramma genus under artificial conditions. These media can be prepared when biological material, such as insect haemolymph, is available, and then stored for later use for several months. The development of two Trichogramma dendrolimi strains from China (TdC) and Italy (TdI) and Trichogramma brassicae (Tb) in rehydrated freeze-dried media was tested with artificial host egg cards. About 5560 artificial host eggs were used in the experiments. The percentages of parasitism, pupation and emergence were similar in rehydrated freeze-dried media stored for 8 months and in fresh media. For TdI, the freeze-dried media centrifuged after rehydration induced a higher percentage parasitism, and media that were not centrifuged induced a higher percentage pupation. This could be due to minor modifications in the balance between free and total amino acids. The development parameters observed varied slightly according to the species or strain of Trichogramma tested (TdC, TdI or Tb). Polyvinyl alcohol smeared on the artificial eggs strongly improved egg laying and reduced the variability of the development parameters. Freeze-drying, which does not alter the performance of the media, is a process suited for the long-term storage of artificial media for parasitoids.     

Laboratory bioassay and greenhouse evaluation of Trichogramma cordubensis strains from Portugal

A simple, inexpensive chamber was developed and tested as an evaluative tool to monitor Trichogramma cordubensis dispersal in the laboratory. The chamber consisted of a continuous, winding channel which was cut into an aluminum block. Wasps were released at one end of the channel and allowed to walk in the channel for 21 h and to parasitize Mamestra brassicae eggs placed 3.4 m from the point of wasp introduction. Comparisons between two T. cordubensis populations demonstrated that one population (TCM) dispersed more in the chamber and located host eggs more successfully than the other population (TCD). Subsequent greenhouse releases confirmed that the TCM population dispersed more readily and had significantly higher parasitism rates on sentinel Ephestia kuehniella eggs on tomato plants. The potential utilization of this chamber as a tool to evaluate quality of Trichogramma populations, mainly dispersal activity, is discussed.     

Parasitism capacity of Trichogramma pratissolii Querino & Zucchi (Hymenoptera: Trichogrammatidae) on alternative hosts, under different temperatures

The successful use of Trichogramma as biocontrol agent depends on its mass production in laboratory, a fundamental step for any biological control program among other factors. This work investigated the parasitism capacity of Trichogramma pratissolii Querino & Zuchi (Hymenoptera: Trichogrammatidae), a new recorded Trichogramma species, parasitizing eggs of Anagasta kuehniella (Zeller) and Corcyra cephalonica (Stainton) (Lepidoptera: Pyralidae) under the temperatures of 15, 18, 21, 24, 27, 30 and 33 degree Celsius. Eggs of these hosts were offered to newly emerged females during 24h. This procedure was repeated daily for each female and each temperature up to female death, in order to estimate daily and accumulated parasitism, and female longevity. On both hosts, the daily parasitism decreased as function of the female age. Under all temperatures studied and both hosts the highest rate of parasitism was observed during the first 24h of host exposure, and reached 80% of total parasitism in the 4th and 3rd days when parasitizing A. kuehniella and C. cephalonica, respectively. On both hosts, the highest parasitism rate was observed under temperatures from 21 degree Celsius to 27 degree Celsius. Average longevities of T. pratissolii females deprived of food emerging from A. kuehniella and C. cephalonica lived for 1.0 and 8.9 days when reared at 15 degree Celsius e 33 degree Celsius, respectively. The results indicate that eggs of A. kuehniella and C. cephalonica and temperatures from 21 degree Celsius to 27 degree Celsius were appropriate to rear T. pratissolii.     

逐日羽化的赤眼蜂品质的比较

本文报道了逐日羽化的赤眼蜂(Trichogramma maidis Pint.et Voeg)品质的比较结果.第1天羽化的雌蜂是群体中生活力最强的个体;第2和第3天羽化的雌蜂生殖力、寿命、个体大小和性比等4项指标逐渐下降;而第4天羽化的雌蜂质量最差.当逐日(第1—第4天)羽化的赤限蜂先分别用地中海粉斑螟卵繁殖1代,然后分别收集第1天内羽化的赤眼蜂试验时,子代(F₁)雌蜂的质量有了明显的提高.母代为第3和第4天羽化的赤限蜂,其子代雌蜂的质量分别超过母代.试验表明,通过实验室选择培养可以改进和提高大量培养赤眼蜂的质量.     

东北地区四种本地赤眼蜂对草地贪夜蛾寄生能力及适应性研究

草地贪夜蛾Spodoptera frugiperda(Smith)是新入侵我国的重大危险性入侵害虫,赤眼蜂是我国生物防治的优势卵寄生蜂,可用于防治多种农林作物上的鳞翅目害虫。为检测东北地区本地赤眼蜂对草地贪夜蛾卵的生防潜能,筛选防治草地贪夜蛾的有效蜂种,本研究比较研究了松毛虫赤眼蜂、玉米螟赤眼蜂、黏虫赤眼蜂和稻螟赤眼蜂对草地贪夜蛾卵的寄生能力和发育适合度。结果表明,4种赤眼蜂均能寄生草地贪夜蛾卵,并完成发育,但其寄生能力和发育适合度存在显著差异。松毛虫赤眼蜂、玉米螟赤眼蜂和黏虫赤眼蜂对草地贪夜蛾卵块寄生率均高于80%,但仅松毛虫赤眼蜂对草地贪夜蛾卵表现出较高的卵粒寄生量。松毛虫赤眼蜂、玉米螟赤眼蜂和黏虫赤眼蜂子代羽化率和雌性比无显著差异,但松毛虫赤眼蜂比其它3种赤眼蜂的发育历期更短,而稻螟赤眼蜂对草地贪夜蛾卵的寄生能力和适合度均最差。研究结果将为应用本地赤眼蜂生物防治潜在入侵东北地区的草地贪夜蛾提供技术支撑。