Biological studies on two neotropical egg parasitoid species: Trichogramma nerudai and Trichogramma sp. (Hymenoptera: Trichogrammatidae)

The main biological attributes of two Neotropical egg parasitoids, the arrhenotokous Trichogramma nerudai and the thelytokous Trichogramma sp., were assessed under controlled laboratory conditions. Developmental time from egg to adult, and parasitoid survival, fecundity and fertility were studied using life tables. Results showed that T. nerudai had a faster developmental time than Trichogramma sp. (13.014±0.4019 and 13.595±0.4931 days, respectively). Both species showed similar life table statistics, r_m was 0.222 and 0.225 for T. nerudai and Trichogramma sp., respectively. Parasitoid survival averaged 95% for both species. The results obtained are discussed in the context of selecting one of these natural enemies as a potential biological control agent for the European pine shoot moth Rhyacionia buoliana (Lepidoptera: Tortricidae) in pine forests and the codling moth Cydia pomonella (Lepidoptera: Tortricidae) in apple orchards in Argentina.     

Effects of deltamethrin on the reproduction of Trichogramma cordubensis (Hymenoptera: Trichogrammatidae)

The influence of deltamethrin on the reproduction of Trichogramma cordubensis, a thelytokous egg parasitoid, was investigated by studying egg maturation and daily fecundity of insecticide treated wasps and offspring emergence rates. The insecticide was applied to the parasitoids at the prepupal stage within its host eggs (Ephestia kuehniella). The total number of parasitized eggs per female during the first 7 days was not significantly influenced by the tested concentrations of deltamethrin. Prevalence of parasitism during this period had a similar pattern between deltamethrin treatments and the control. In addition, the mean number of mature eggs observed per female per day was significantly correlated to mean daily fecundity, regardless of the treatments. Offspring emergence was significantly influenced by the insecticide treatments experienced on their progenitors, decreasing significantly at 48 and 72 h for the highest tested concentration of deltamethrin (23.6 mg [a.i.]/L). Despite that, deltamethrin had no adverse effects on the reproduction of treated wasps, particularly when was applied at the concentration recommended by the manufacturer (12.5 mg [a.i.]/L).     

Isolation and characterisation of 26 polymorphic microsatellite markers for the parasitoid wasp Trichogramma dendrolimi (Hymenoptera: Trichogrammatidae)

Polymorphic microsatellite markers were developed for the parasitoid wasp Trichogramma dendrolimi. Forty-four microsatellites were isolated from a (TCG)₈-enriched genomic library and characterised. Twenty-six of these loci were polymorphic and could be used for evaluation of the genetic variation of T. dendrolimi.     

Naturally occurring egg parasitoids of the genus Trichogramma (Hymenoptera: Trichogrammatidae) in a pomegranate orchard in Tunisia

Four Trichogramma species were found in a pomegranate orchard in Gabès, an arid region of Tunisia, from parasitized eggs of Ectomyelois ceratoniae Zeller (Lepidoptera: Pyralidae), an economically important insect pest. Identification based on assessment of male genitalia and internal transcribed spacer 2 ( ITS 2) sequences showed that they were T. bourarachae Pintureau and Babault, 1988, T. oleae Voegelé and Pointel, 1979, T. cacoeciae Marchal, 1927 and T. evanescens Westwood, 1833. Trichogramma evanescens is reported for the first time in Tunisia. Trichogramma cacoeciae was the largely dominant species in the analyzed samples, whereas T. bourarachae was present in a minor portion of 1.38%. The implications of these results for attempts at controlling E. ceratoniae are discussed.     

Experience acquisition by Trichogramma australicum Girault (Hymenoptera: Trichogrammatidae)

We investigated experience acquisition (alpha-conditioning) by females of the parasitoid Trichogramma australicum using host eggs of the noctuid moth Helicoverpa armigera (Hübner). We compared the acceptance of a host egg by females with different levels of ovipositional experience. The level of experience was designated using the standard oviposition sequence: (1) host contact (C); (2) host examination (E); (3) drilling (D); (4) full insertion (FI); and (5) oviposition (O). Each treatment consisted of a single experience level, but together these consituted a qualitative behavioural continuum of oviposition experience from naive (N) to experienced wasps. We found that host experience by adult T. australicum females can modify their behaviour. Mean duration of host finding was: N = C > E = D > FI = O. Mean duration of host examination and full insertion were: N = C > E = D = FI = O. Drilling was constant for all experience levels. Experience in drilling of the chorion during the previous host-exposure process represents a critical experience for a female and results in efficient handling and more ready acceptance of a subsequently encountered host egg.     

Odor specificity testing in the assessment of efficacy and non-target risk for Trichogramma ostriniae (Hymenoptera: Trichogrammatidae)

Trichogramma ostriniae Pang and Chen (Hymenoptera: Trichogrammatidae) is an indigenous egg parasitoid of Ostrinia furnacalis Guenée (Lepidoptera: Crambidae) in China. We evaluated T. ostriniae's responses in olfactometer and wind tunnel assays to various host and plant odors that are likely to impact the efficacy and non-target risk of utilizing T. ostriniae as an augmentative biocontrol agent against Ostrinia nubilalis Hübner in the USA. In a Y-olfactometer, female T. ostriniae exhibited innate positive responses to the egg mass volatiles, scale volatiles, and synthetic sex pheromones of O. nubilalis. When exposed to O. nubilalis pheromone while walking on a platform in a wind tunnel, the wasps manifested significant changes in patch exploration behavior, including delayed dispersal from the platform and slowed walking. The wasps did not respond innately to the synthetic pheromone of a non-target species, Spodoptera frugiperda J. E. Smith (Lepidoptera: Noctuidae), however. Exposing wasps to S. frugiperda pheromone together with eggs of a factitious rearing host prior to testing also did not alter the wasps’ lack of response to the pheromone, indicating that associative learning of the novel odor did not occur. Lastly, wasps showed no innate responses to leaf volatiles from corn (Zea mays L.) and pepper (Capsicum annuum L.), two crops attacked by O. nubilalis. We conclude that T. ostriniae is likely to be highly efficient at finding O. nubilalis eggs in the field through the exploitation of host chemical cues. Further, T. ostriniae's response to moth pheromone appears to be relatively host-specific, since the wasps responded to the pheromone of a congener to their natural host, but not to the pheromone of a more distantly related non-target species. This type of odor-specificity could be an important mechanism for reducing the risk of T. ostriniae attack on non-target species.     

Temperature-dependent Development of Four Egg Parasitoid Trichogramma Species (Hymenoptera: Trichogrammatidae)

Trichogramma species have been successfully utilized for biocontrol of several lepidopteran pests worldwide. The development, survival and progeny production of two Kenyan species' Trichogramma bournieri Pintureau & Babault and Trichogramma sp. nr. mwanzai Schulten & Feijen (collected from Kenya), Trichogramma evanescens Westwood (Germany) and Trichogramma chilonis Ishii (India) was studied at four constant temperatures (13, 18, 25 and 34°C) with the 011 aim of assessing the relative biotic potential of the two native species for 011 biocontrol of Helicoverpa armigera and Plutella xylostella in Kenya. The study was conducted at the Institute 011 for Biological Control (BBA), Darmstadt, Germany. The Trichogramma species tested showed variations 011 in fertility, developmental time, percent emergence, progeny production and sex ratio 011 at the four temperature regimes. Fertility decreased as temperature increased from 25 to 34°C. 011 T. chilonis and T. evanescens completed development at all temperatures tested, but T. 011 bournieri and T. sp. nr. mwanzai failed to complete development at 13°C. The developmental 011 period for all the species decreased as the temperature increased. The duration of development from 011 oviposition to adult emergence varied from 8 days to 12 weeks shorter at 34°C than at 011 13°C for T. chilonis and T. evanescens . For the various temperatures tested, a linear model was 011 satisfactory for egg to adult development at P = 0.05 for T. chilonis and T. evanescens . The 011 lower temperature thresholds for development and duration in degree-days were 8.83°C and 188 for 011 T. chilonis and 9.23°C and 192 for T. evanescens , respectively. For all temperatures tested, 011 T. sp. nr. mwanzai had the highest preimaginal survivorship. Adult emergence was lower at 13°C and 34°C than at 011 18 and 25°C. The highest fertility (mean ±SE) (50.37 ±2.32 adult 011 female -1 ) and progeny production (44.03 ±2.02 adult female -1 ) was recorded at 25°C for 011 T. evanescens . Sex ratio was biased towards female at all temperatures in T. bournieri and T. chilonis . 011 At all temperatures tested, T . sp. nr. mwanzai produced more males than females. For all species tested, 011 favourable parasitism was between 18 and 25°C. The results from this study will be useful for mass rearing purposes as well as for future field release programmes.     

Development of a continuous cell line from the insect egg parasitoid,Trichogramma pretiosum (Hymenoptera; Trichogrammatidae)

Summary A cell line (IPLB-TpE1) was established from embryos of the hymenopteran parasitoid,Trichogramma pretiosum Riley. Cultures contain a mixture of attached, elongate spindle-shaped cells and large aggregates of suspended cells. Chromosomes of the cells were typical ofTrichogramma species and isozyme characterization showed patterns similar toT. pretiosum adults, but distinctly different fromHeliothis zea, the lepidopteran host from which parasite eggs were obtained. The cells are capable of growth over a wide range of osmotic pressures with equal growth between 350 and 600 mOsm/kg. Optimal growth was obtained with a pH of 6.5. Doubling time at the 40th passage was 72 h and cultures are currently subcultured at weekly intervals. The mention of a commercial product does not constitute an endorsement by the U. S. Department of Agriculture.     

Parasitization of potato tuber moth eggs (Lep., Gelechiidae) from irradiated adults by Trichogramma (Hym., Trichogrammatidae) and control of moth population with combined releases of sterile insect and egg parasitoid

Abstract:  Eggs of the potato tuber moth (PTM) Phthorimaea operculella (Zeller) obtained from 150 or 300 Gy-irradiated moths, either inbred or out-crossed to untreated counterparts, were offered as host material to three generalist Trichogramma species; Trichogramma cacoeciae , Trichogramma evanescens , and Trichogramma principium , to determine the ability of these egg parasitoids to develop in F₁ sterile eggs. All eggs laid by the different parental crosses at 150 or 300 Gy, were acceptable and suitable for Trichogramma development. However, in no choice and paired comparison tests, eggs from 300 Gy-irradiated parents were significantly less preferred compared with eggs laid by non-irradiated moths. No intra-specific differences for PTM sterile eggs were recorded among the tested Trichogramma species. The mean number of wasps emerging from each egg types was not affected by an interaction between parental crosses and applied doses. Overall, this study demonstrates that release of irradiated and non-irradiated moths at a 5 : 1 over-flooding ratio and Trichogramma over potatoes in small plexiglass boxes, is complementary and more effective in reducing PTM F₁-emerged progeny than either technique used alone. The results provide baseline data for developing an integrated control approach by using inherited sterility technique in conjunction with Trichogramma for PTM population suppression.     

Factors affecting the bionomics of the eastern African egg parasitoid Trichogramma bournieri Pintureau & Babault (Hymenoptera: Trichogrammatidae)

The trichogrammatid Trichogramma bournieri Pintureau & Babault is a polyphagous parasitoid of eggs of several cereal stemborer species in eastern Africa. The effects of host species, host age and duration of host deprivation on the performance of the parasitoid were studied in the laboratory. Host acceptance and suitability were tested using five stemborer species. The noctuids Sesamia calamistis Hampson, Sesamia nonagrioides (Lefebvre), Busseola fusca (Fuller) the crambid Chilo partellus (Swinhoe) and the pyralid Eldana saccharina Walker were successfully parasitized by T. bournieri. Parasitism, number of progeny and developmental time varied significantly with host species. The eggs of S. calamistis and B. fusca were the most suitable, whereas those of E. saccharina were the least suitable. While parasitism and number of progeny tended to decrease with age of hosts, there were no significant differences in sex ratio. Longevity of the parasitoid increased with increase in deprivation of hosts from 0 to 12 days. Average lifetime fecundity per female decreased, indicating resorption of eggs.     

Flight initiation in the egg parasitoid Trichogramma minutum: Effects of ambient temperature, mates, food, and host eggs

Emergence, preening, and flight initiation were studied in laboratory-reared Trichogramma minutum Riley (Hymenoptera: Trichogrammatidae). Male parasitoids emerged first and flew before females. When both sexes were present in flight cylinders, female parasitoids flew before males. Flight propensity in males was negatively related to the number of emerging females, while flight propensity in females was independent of the number of males present. Ambient temperature significantly affected the propensity and timing of flight; between 70–80% of the parasitoids flew at 25 and 30 °C while less than 4%, mostly males, flew at 20 °C. No flights were observed at 15 °C. The presence of fresh host eggs caused a reduction in the proportion of female parasitoids that flew and a delay in the time to flight for the females that did fly. The presence of food increased the flight propensity of female parasitoids, but did not affect the timing of flight. The relationship between flight behaviour and the efficiency of mass-reared Trichogramma is discussed in terms of its importance for inundative release programmes.     

Comparison of different European strains of Trichogramma aurosum (Hymenoptera: Trichogrammatidae) using fertility life tables

Life table parameters were assessed for seven strains of Trichogramma aurosum Sugonjaev and Sorokina (Hymenoptera: Trichogrammatidae) collected in different European countries, in order to compare their performance when reared on eggs of Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) as a potential factitious host for mass-rearing. The average number of progeny per female, cumulative fertility and emergence rate did not differ significantly, whereas female longevity and sex ratio significantly differed between the seven parasitoid strains. The Danish strain survived the longest (6.05 days) and the Dutch strain survived the shortest (2.75 days). Progeny was always female-biased with varying proportions (57.7-96.7%). Survival rates started to decrease after 3 days for some of the strains studied. The mean cohort generation duration (T_c) was 11.40, 10.15, 10.62, 10.63, 9.28, 9.70 and 11.30 days for the Austrian, Luxemburgian, Belgian, French, Dutch, Danish and German strains, respectively. Population doubling time (D_t) was 4.50, 7.96, 3.56, 5.30, 5.23, 7.36 and 3.30 days, respectively. Daily intrinsic rate of increase (r_m) and finite rate of increase (exp. r_m) ranged between 0.087 and 0.210 and 1.091-1.233, respectively. The German strain might be a potential candidate for mass rearing and releases against the codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae), due to its high net reproduction rate (R₀=10.65 female), a high intrinsic rate of natural increase (r_m=0.210), a high finite rate of increase (exp. r_m=1.23), and a short population doubling time (D_t=3.3 days). The relevance of intra- and interstrain variability as well as the usefulness of fertility life tables for pre-introductory research is discussed.     

Trichogramma ostriniae (Hymenoptera: Trichogrammatidae) response to relative humidity with and without host cues

Trichogramma ostriniae is a parasitoid wasp species that is used as a biological control for several lepidopteran agricultural pests. Our study examined the effects of relative humidity (RH) on the behaviour of female T. ostriniae. In Y-tube RH choice assays, wasps generally chose higher RH over lower RH but the latency time taken to make a choice displayed no clear patterns that could be ascribed to the magnitude of the RH difference between arms of the Y-tube. In trials conducted in glass arenas with fixed humidities, the conditional probabilities of transition from searching to interacting with the leaf disk, and from interacting with leaf disks to antennal egg drumming and oviposition, were not significantly different among the RH levels, nor were there differences in latency times. These findings suggest that the level of RH may influence habitat choice but have little effect on search efficacy.     

Temperature and strain effects on reproduction and survival of Trichogramma oleae and Trichogramma cacoeciae (Hymenoptera: Trichogrammatidae)

To assess differences in temperature sensitivity during development, life tables for two lines derived from the species Trichogramma oleae Voegelé and Pointel and a strain of Trichogramma cacoeciae Marchal (Hymenoptera: Trichogrammatidae) were elaborated at 15, 20, 25, 30, 35, 36, and 37°C in the laboratory. Eggs of Ephestia kuehniella Zeller together with a fresh drop of honey were supplied every 2 days until the death of the test females, and the removed host egg batches were placed in the equivalent rearing cabinet. The line ‘2F’ of T. oleae was found to be the most efficient at any range of temperatures except at 20 and 37°C, in comparison to the other tested strains. For all species, no progeny emerged from eggs incubated at 36°C and none of the parasitized eggs turned black at 37°C. The better performance at a broader range of temperatures by T. oleae (line 2 F) might be caused by a shorter history in artificial rearing in comparison to the other strains. Fewer generations at laboratory conditions and frequent multiplication on eggs of its natural host (the olive moth Prays oleae) may have prevented a deterioration in the rearing population of this strain, maintaining its genetic diversity at a higher scale. Applying varying temperature regimes on the rearing stock at regular intervals during the mass production process may help to maintain the essential quality of the biological control agents for field performance at higher temperatures.     

Development of Trichogramma australicum Girault (Hymenoptera: Trichogrammatidae) in Helicoverpa (Lepidoptera: Noctuidae) host eggs

Abstract Morphological studies of development of the egg parasitoid Trichogramma australicum Girault in the cotton bollworm, Helicoverpa armigera (Hübner), were conducted to provide benchmarks for assessing developmental rates in both natural hosts and artificial diets. Observations of living embryos and histological sections show that embryos proceed rapidly through cleavage and blastoderm formation and show a characteristic pinching or rotation 8 h after deposition. Eggs progressively increase in volume, primarily by increasing in diameter at the widest point. At 29 ± 1°C the duration of the egg stage is 22−24 h, the larval stage 27 h, the prepupal stage 50−52 h, and pupa 85 h. Larvae undergo dramatic shape changes as they ingest food but do not show signs of larval moults, reinforcing observations that there is only one larval instar. Criteria for staging the embryonic and postembryonic development in natural hosts will be used for future studies aimed at developing and refining artificial diets for Trichogramma.     

Diapause induction in Trichogramma embryophagum Htg. (Hym., Trichogrammatidae): the dynamics of thermosensitivity

It is known that the low temperature is the most important factor inducing the pre-pupal diapause in Trichogramma species. The position of the thermosensitive period over the life cycle and temporal variation of the degree of responsiveness were investigated in T. embryophagum Htg. by transferring pre-imaginal stages between 'neutral' temperature of 15°C and 'diapause-inducing' temperature of 10°C. Our experiments showed that 6 days long exposure at 10°C significantly increased the percentage of diapausing pre-pupae when started during rather large part of development: from embryo up to early pre-pupa. The highest thermosensitivity was recorded during the embryo and the larval stages, with some decrease during the hatching period. Treatments with shorter cold exposures (2–3 days) gave similar results. Even 24 h long exposure at 10°C increased the percentage of diapausing pre-pupae when applied during egg or early larval stage. Being started at the same stage of development, longer cold exposures caused stronger increase in the percentage of diapausing individuals. The experiments did not reveal any significant daily changes in thermosensitivity: at 12 : 12 h light : dark, larvae subjected to the low temperature during six photophases showed practically the same percentage of diapausing individuals as those subjected to the low temperature during six scotophases, and as those subjected to the 3 days long uninterrupted cold exposure. Hence, in natural conditions even occasional short-term cold periods could be accumulated.     

Effect of host egg viability on reproduction and development of Trichogramma cacoeciae and T. principium (Hymenoptera: Trichogrammatidae)

A combination of a sterile insect technique, resulting in infertile eggs, and of an egg parasitoid, should provide better control of codling moth than either alone. Non-choice laboratory experiments were conducted with infertile and fertile codling moth eggs to evaluate the potential parasitism and reproduction of Trichogramma cacoeciae Marchal and T. principium Sug. et Sor. The tendency of T. cacoeciae females to attack infertile eggs was similar to that for fertile eggs, whereas T. principium showed a greater preference for infertile eggs than fertile eggs. The fertility status of the host did not affect the number of eggs that were parasitized but fewer F₁ progeny emerged from infertile eggs when parasitized than from fertile eggs. When T. cacoeciae and T. principium parasitized infertile host eggs their mean developmental time was prolonged but the viability and quality of parasitoid progeny was not influenced by the fertility status of the host eggs. The study demonstrates the compatibility of use of T. cacoeciae and T. principium in an integrated program employing the sterile insect technique for codling moth management.     

Two new egg parasitoids (Hymenoptera: Encyrtidae) of the wood borer Agrianome spinicollis (Macleay) (Coleoptera: Cerambycidae), a pest of pecans in eastern Australia

Abstract Baeoanusia xanthopleuron sp. n. and Avetianella coombsi sp. n. (Hymenoptera: Encyrtidae) are described from New South Wales and Queensland. Photomicrographs are provided to illustrate morphological characters of both species, and their systematic position is discussed on the basis of their morphology and biology. Both species are egg parasitoids of the wood borer Agrianome spinicollis (Macleay), an important pest of pecans in eastern Australia.     

Maternal influence on diapause induction in Trichogramma (Hymenoptera: Trichogrammatidae): the dynamics of photosensitivity

It is known that the prepupal diapause in Trichogramma is dependent on temperature conditions of embryonic and larval development and on the photoperiodic conditions of preimaginal development of maternal females. However, the relative photosensitivity of different preimaginal stages has been never investigated. We studied the position of the photosensitive period over the preimaginal development of maternal females in T. embryophagum Htg. and T. principium Sug. et Sor. by transferring preimaginal stages between diapause‐averting ‘long’ day (L : D = 20 : 4) and diapause‐inducing ‘short’ day (L : D = 12 : 12). Results showed that the influence of maternal photoperiod on progeny diapause was determined during the late pupal stage (last days of preimaginal development at 20°C). During this time, the critical duration of the photoperiodic induction was extremely small: one short or long day caused almost the same effect as the permanent development under these conditions. As a whole, photoperiodic response in Trichogramma was found to be unusually rapid, labile and easily reversible which is probably explained by extremely small size and fast development of these egg parasitoids. The results of this study could be used for elaboration of optimal methods for Trichogramma mass rearing and storage and for prediction of its seasonal cycles under natural conditions.