Trichogramma Nr Research Articles

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.

Effects of methoxyfenozide, indoxacarb, and other insecticides on the beneficial egg parasitoid Trichogramma nr. brassicae (Hymenoptera: Trichogrammatidae) under laboratory and field conditions.

Trichogramma nr. brassicae is a common egg parasitoid of Helicoverpa species in Australian processing tomatoes, but its effectiveness can be severely curtailed by insecticide applications. To identify insecticides that are potentially compatible with this species, the effects of seven insecticides, including newly introduced compounds and a surfactant, were screened in laboratory and glasshouse assays for their toxicity to the wasps. Assays involved direct applications on adults, residual effects on adults, and applications on life stages still inside the host. Methoxyfenozide and indoxacarb were not toxic to Trichogramma in any assay when applied at field rates. Naled and chlorfenapyr caused 100% mortality when directly applied to adults, and 95% mortality when adults were exposed to residues of these chemicals within 24 h of application. The effects of naled residues were short lived (<48 h). Naled and chlorfenapyr were also toxic when applied to Trichogramma developing inside host eggs, reducing emergence of adults by >25%. Imidacloprid, emamectin, and tau-fluvalinate were toxic in some experiments; they caused >97% mortality in adults 1 h after direct application and in residue assays they caused 23-64% mortality during the first 24 h. In field trials, methoxyfenozide had no harmful effects on emergence from sprayed parasitized eggs, whereas indoxacarb had a small impact (<8%) on emergence. Methoxyfenozide and indoxacarb are potentially suitable for inclusion in integrated pest management strategies for management of Helicoverpa because they do not influence adult survival or development of immature stages, whereas other chemicals need to be treated cautiously.

Composite asymmetry as an indicator of quality in the beneficial wasp Trichogramma nr. brassicae (Hymenoptera: Trichogrammatidae).

Trichogramma are egg parasitoids that are widely cultured for the control of moth pests in commercial insectaries. Stock quality is often maintained by releasing wasps from a mass culture in an area with target host eggs and initiating fresh stocks from parasitized eggs. Here we test if variability among individuals as measured by fluctuating asymmetry can be used as an additional method of quality control in Trichogramma nr. brassicae by comparing fluctuating asymmetry levels between a random sample of wasps before release and wasps that successfully reach host eggs. Although the asymmetry of individual traits was not associated with wasp fitness, a total asymmetry measure based on combining the uncorrelated asymmetries of nine traits did predict the ability of wasps to reach the eggs.

Effect of food on longevity of adults of Trichogramma carverae Oatman and Pinto and Trichogramma nr brassicae Bezdenko (Hymenoptera: Trichogrammatidae)

Abstract Trichogramma spp. are among the most widely used biological control agents against lepidopteran pests. Several species are known to benefit from adult foods, especially plant nectar, but no information has been available on the requirements of Trichogramma carverae Oatman and Pinto, a newly commercialised species, or Trichogramma nr brassicae Bezdenko. In a laboratory test, adults of T. carverae in vials without food eclosed from host eggs and all died within 7 days. In vials with honey, live adults were evident for 11 days. Significantly more live adults were present in vials with honey for days 3–5 after first emergence (P &lt; 0.05). A quadratic model accounted for 28.6% of the temporal variance in data and showed that the rate of increase in numbers of wasps per vial was significantly greater in the fed treatment (P = 0.006). For T. nr brassicae, adults in the unfed vials died within 6 days of eclosing, while those in the honey‐provisioned vials were living up to 13 days from eclosion. Significantly more live adults were present in vials with honey for days 4–7 from first emergence (P &lt; 0.05). The model that accounted for the most variation was a spline model with four knot points, accounting for 42.6% of variation, however, there was no significant effect of food treatment on the rate of increase in wasp numbers in this model. Results are discussed in relation to the use of habitat manipulation to enhance parasitoid effectiveness in biological control.

Acclimation for heat resistance inTrichogrammanr.brassicae: can it occur without costs?

1. It is well known that animals can increase their stress resistance by prior exposure to sub-lethal conditions, but this acclimation process is often accompanied by deleterious fitness effects. These may reflect a cost of acclimation, or more general costs arising from damage due to sub-lethal exposures. 2. Acclimation for increased adult resistance to a 40 °C heat shock was tested in the egg parasitoid, Trichogramma nr. brassicae, following exposure of immature stages to 33 °C for different periods. Prepupal exposure did not increase heat resistance, but daily exposures at the pupal stage for 2 h day−1 and 3 h day−1 over 4 days increased survival of the shock. 3. Pre-pupal exposure for 3 h day−1 over 4 days led to decreased parasitism reflecting general damage costs. Pupal exposure for 3 h day−1 and 4 h day−1 also decreased parasitism rates, but there were no deleterious effects when pupae were acclimated for 2 h day−1. 4. These findings indicate that acclimation can occur without costs in Trichogramma nr. brassicae and suggest a general phenotypic approach for separating acclimation costs from other fitness costs caused by sub-lethal exposures. The potential for using acclimation to increase field parasitism success of this important group of parasitoids is discussed.

Plant cues influence searching behaviour and parasitism in the egg parasitoid Trichogramma nr. brassicae

Abstract.1. The effect of experience of plant cues at emergence on searching behaviour and parasitism was investigated in two strains of Trichogramma nr. brassicae (Hymenoptera: Trichogrammatidae).2. Wasps reared on Sitotroga cereallela were allowed to emerge on a tomato plant or in a vial, with or without food. For one of the strains, females emerging on tomato searched significantly longer on a tomato seedling than females emerging in a vial.3. The experience effect lasted between 1 and 2 days. It involves associating plant stimuli with the remains of the host, because females emerging from their host on a tomato plant had an increased searching response to tomato, but females transferred to the plant immediately after emergence did not.4. The effect of emergence environment on parasitism of the host Helicoverpa punctigera on tomato and lettuce seedlings was tested. Wasps were allowed to emerge on seedlings of tomato or lettuce, or in an empty vial. For one strain, females experienced with tomato at emergence parasitized significantly more hosts on tomato than did females emerging on lettuce or in a vial. Parasitism on lettuce was not influenced by the treatments.

Persistence of experience effects in the parasitoid Trichogramma nr. brassicae

1. The importance of learning in parasitoids is likely to depend on how long learning effects persist, the number of learned stimuli that can be retained, and whether learning effects are confined to low ranked hosts.2. The duration of learning of host‐specific stimuli was tested in four strains of Trichogramma nr. brassicae (Hymenoptera: Trichogrammatidae). Both the persistence of learning of the rearing host and oviposition experience were tested in separate experiments.3. The response to a non‐preferred host, Sitotroga cerealella, was measured at different times following experience on that host or an alternative host, Heliothis punctigera. Both types of experience persisted for at least 5 days in all four strains.4. The effect of oviposition in a highly preferred host, H. punctigera, following oviposition in S. cerealella was also tested. The increased acceptance of S. cerealella following oviposition on this host persisted despite a subsequent oviposition on H. punctigera.5. The implications for host range at both individual and population levels are discussed.

An evaluation of selective Helicoverpa armigera control options in sweet corn

Summary. Helicoverpa armigera is a serious insect pest of sweet corn in Australia and is becoming increasingly difficult to manage with conventional chemical insecticides due to resistance problems. A number of alternative H. armigera control options were evaluated in sweet corn and compared with deltamethrin and no action (control). The alternative tactics evaluated were: heliothis nuclear polyhedrosis virus plus Trichogramma nr. brassicae releases; Bacillus thuringiensis; and Trichogramma alone. The H. zea nuclear polyhedrosis virus + Trichogramma plots had the lowest cob damage (6.0%), followed by the B. thuringiensis plots (12.0%), Trichogramma alone plots (20.2%), control plots (23.2%) and deltamethrin plots (53.5%). There was no evidence to suggest that the Trichogramma nr. brassicae releases had any impact on H. armigera egg mortality. However, there was a large natural population of Trichogramma pretiosum in all plots. The application of deltamethrin reduced the action of these wasps and predators, resulting in higher larval infestation and significantly more cob damage. The findings indicate that the pathogens heliothis nuclear polyhedrosis virus and B. thuringiensis can effectively control H. armigera when their action complements high natural levels of egg parasitism, and that they have potential for use in integrated pest management programs in sweet corn.

Separating the Effects of Experience, Size, Egg Load, and Genotype on Host Response in Trichogramma (Hymenoptera: Trichogrammatidae)

The effects of experience, egg load, and wasp size on the response of four strains of Trichogramma nr. brassicae (Hymenoptera: Trichogrammatidae) to three economically important hosts, Heliothis punctigera (Noctuidae), Phthorimaea opercullela (Gelechiidae), and Sitotroga cereallela (Gelechiidae) were investigated. Experience effects due to rearing host and oviposition were considered in all combinations of host species. Both these effects altered response levels to low-ranked hosts but not to highly preferred hosts. Size was correlated with host response in some strains; larger females took more encounters with a host before accepting it, while egg load was not correlated with number of host encounters. However, egg load, rearing host, and size all affected acceptance of the low-ranked host S. cereallela. Females were more likely to accept this host if they were reared on S. cereallela, had a small size, and had a high egg load. Effects were consistent across strains, although overall acceptance levels differed among strains.

Inbreeding and incompatibility in Trichogramma nr. brassicae: evidence and implications for quality control

AbstractInbreeding effects and incompatibility relationships were examined in strains of the egg parasitoid Trichogramma nr brassicae (Hymenoptera: Trichogrammatidae) from southeastern Australia. Crosses between strains provided weak evidence of incompatibility in a few cases. However, sex ratio in crosses within strains tended to be more female‐biased than in crosses between strains. Inbreeding was imposed for four generations (F&gt;0.59) of sib mating. The fitness of inbred strains was compared to that of outbred strains generated by crossing the inbred strains. No effects of inbreeding were found for any of the four female traits examined (fecundity, body length, head width and hind tibia length), indicating that T. nr. brassicae is not subjected to inbreeding depression. Inbreeding effects were also not found for male mating success as expected for the haploid sex. There were differences among strains for all traits apart from fecundity, indicating heritable variation. Strain differences for fitness measures were uncorrelated with wasp size. The potential use of inbreeding in the quality control of Trichogramma for mass‐release is discussed. Inbreeding may be a useful tool in minimising the effects of laboratory adaptation, thereby extending the useful life of a strain.

Effects of pre‐adult and adult experience on host acceptance in choice and non‐choice tests in two strains of Trichogramma

AbstractThe effect of adult learning through an oviposition experience, and pre‐adult learning through development inside a host was investigated in two strains of an Australian egg parasitoid, Trichogramma nr ivelae (Hymenoptera: Trichogrammatidae). Host response was measured in two types of laboratory preference tests. In single host tests, females reared on three lepidopteran hosts (Heliothis punctigera (Noctuidae), Papilio aegeus (Papilionidae), and Hypolimnas bolina (Nymphalinae)) were presented host eggs individually, and allowed two ovipositions. Pre‐adult experience affected host preference in only one strain, while acceptance of a host was increased in both strains when they had previously oviposited in this host species. An oviposition experience had a stronger effect on host preference than pre‐adult experience. In choice tests, pairwise combinations of hosts were arranged in an alternating grid. The ratio of host acceptances to host contacts was computed for the whole test and up to the first oviposition. These indicated that effects of rearing host were weak or absent, but the host chosen initially had a strong effect on host preference. Relative size of the hosts had a strong effect on choice of the first host. The implications of learning in Trichogramma are discussed in relation to host preference testing procedures and the selection of candidate strains for mass rearing and inundative release.

Assessment of Trichogramma species for biological control of forest lepidopteran defoliators

AbstractIn a laboratory study, we determined the potential of three Trichogramma (Hymenoptera: Trichogrammatidae) species, T. brassicae Bezdenko, T. minutum Riley and T. nr. sibiricum Sorokina, for biological control against six species of forest lepidopteran pests, black army cutworm, hemlock looper, eastern spruce budworm, western spruce budworm, white‐marked tussock moth, and gypsy moth. Females of each parasitoid species were offered eggs from each of the six host species. Parasitization and the effect of the host species on the emerging progeny were examined and recorded. Trichogramma minutum had the broadest host range and successfully parasitized four host species out of the six offered. Trichogramma nr. sibiricum had the narrowest host range and parasitized only two species of hosts. Of the six host species, black army cutworm was the most preferred by all three Trichogramma species; white‐marked tussock moth and gypsy moth were not parasitized by any parasitoids. There was a positive correlation between the size of female offspring and their corresponding egg complement in all three parasitoid species. The developmental time of parasitoids from egg to adult was influenced by both the parasitoid and host species. Our results suggest that T. minutum has the greatest potential for biological control against various forest lepidopteran pests and that the black army cutworm may be the best target candidate for further study.