Using Trichogramma Westwood (Hymenoptera: Trichogrammatidae) for insect pest biological control in cotton crops: an Australian perspective

Biology, Thermal Requirements, and Fertility Life Table of Strains of Trichogramma foersteri (Hymenoptera: Trichogrammatidae) in Palpita forficifera (Lepidoptera: Crambidae)

Trichogramma foersteri Takahashi is a parasitoid recently identified in eggs of Palpita forficifera Munroe, considered the main pest of the olive tree in Brazil. The efficiency of a parasitoid is conditioned to several factors such as the temperature. The objective was to study the biology of the immature and adult phases at different constant temperatures (10, 15, 20, 25, and 30 °C), determine thermal requirements, and to elaborate a fertility life table for five strains (R1, R2, R3, R4, and R5) to T. foersteri. At 10 °C, there was no development of T. foersteri. The duration of the egg-adult period (days) was inversely related to temperature, ranging from 32 to 34 days (at 15 °C) to 6.5 to 7.5 days (at 30 °C). The thermal range evaluated did not influence parasitism (parasitism > 57%) and the sex ratio (sr > 0.74). The base temperature (Tt) was similar for all strains (approximately 12 °C), corresponding to a thermal constant (K) of 120.48 to 145.13 degree days. For the adult stage, T. foersteri had the highest rate of parasitism (> 48%) to 15 °C. The emergence rate ranged from 75 to 100%. The thermal range did not influence the sex ratio of the lines (sr > 0.70), but reduced the longevity from 50 days (at 15 °C) to 6 days (at 30 °C). Regarding the fertility life table, all strains of T. foersteri showed biological potential of development and growth in eggs of P. forficifera in the thermal range of 15 to 30 °C, important information for the establishment of biological control programs.

Effect of Ephestia kuehniella (Lepidoptera: Pyralidae) Larval Diet on Egg Quality and Parasitism by Trichogramma brassicae (Hymenoptera: Trichogrammatidae)

Trichogramma spp., among the most common parasitoids used for augmentation biological control, often are mass-reared on eggs of the Mediterranean flour moth, Ephestia kuehniella (Zeller). To evaluate removal of nutritional components from the E. kuehniella larval diet and reduce production costs, colonies were maintained using one of three diets: a standard diet consisting of eight ingredients, a reduced diet containing whole wheat flour, glycerol, and Brewer's yeast, or a third minimal diet of only whole wheat flour. The standard diet sustained the fastest larval development, female pupae with the greatest mass, the highest level of adult emergence, and production of the most eggs per female. Eggs from moths reared as larvae on the standard or reduced diet had equivalent mass, length, and percent hatch. Females from larvae fed the minimal diet produced eggs with the least mass that were shorter and had the lowest percent hatch. Eggs from the three E. kuehniella colonies were exposed separately to Trichogramma brassicae Bezdenko females to determine their acceptance for oviposition. More of the eggs from the standard diet were parasitized by the females, eggs from the reduced and minimal diets being less acceptable. The percent emergence of the parasitoids was the same regardless of diet; however, the largest wasps emerged from the standard diet eggs and a greater proportion of them were females. Consequently, the standard E. kuehniella larval diet resulted in the highest rate of reproduction and robust eggs that produced superior T. brassicae wasps.

Thermal Requirements and Performance of the Parasitoid Trichogramma pretiosum (Hymenoptera: Trichogrammatidae) on Helicoverpa armigera (Lepidoptera: Noctuidae) Eggs Under Variable Temperatures

Temperature causes physiological and behavioral changes in egg parasitism. Egg parasitoids are a possible alternative for the control of Lepidoptera pests. The cotton bollworm Helicoverpa armigera (Hübner) is a generalist pest that has recently been introduced into Brazil. We evaluated the suitability of H. armigera eggs as hosts for Trichogramma pretiosum Riley and the effects of temperature (18-33°C) on its survival and development. We assessed the developmental time (egg adult), thermal requirements, age-specific fertility, and parasitism rate upon eggs of H. armigera at six different temperatures. Linear and nonlinear (Brière2) models were fitted to our data in order to describe the relationship between developmental rate and temperature for the immature stages of T. pretiosum and estimate the thermal constant (K), lower developmental temperature threshold (LT), optimum temperature for development (Topt), and upper developmental temperature threshold (Tmax). The estimated K and LT estimated by linear model were 130.38 degree days and 10.3°C, respectively. The T0, Topt, and Tmax by Brière model were 11.52, 32.89, and 41.1°C, respectively. Females of T. pretiosum developed at each temperature were assessed, and parasitism rate was above 75% on the first day, except at 30°C where it took 2 d to reach 75%. At 33°C, the highest rate of parasitism was 38%. The life table parameters predict population increases across the temperature range evaluated. The results demonstrated that T. pretiosum are suitable for the control of H. armigera, and the best performance will be achieved when used in regions with temperatures up to 30°C.

A perspective on management of Helicoverpa armigera: transgenic Bt cotton, IPM, and landscapes

Helicoverpa armigera is a major pest of agriculture, horticulture and floriculture throughout the Old World and recently invaded parts of the New World. We overview of the evolution in thinking about the application of area-wide approaches to assist with its control by the Australian Cotton Industry to highlight important lessons and future challenges to achieving the same in the New World. An over-reliance of broad-spectrum insecticides led to Helicoverpa spp. in Australian cotton rapidly became resistant to DDT, synthetic pyrethroids, organophosphates, carbamates and endosulfan. Voluntary strategies were developed to slow the development of insecticide resistance, which included rotating chemistries and basing spray decisions on thresholds. Despite adoption of these practices, insecticide resistance continued to develop until the introduction of genetically modified cotton provided a platform for augmenting Integrated Pest Management in the Australian cotton industry. Compliance with mandatory resistance management plans for Bt cotton necessitated a shift from pest control at the level of individual fields or farms towards a coordinated area-wide landscape approach. Our take-home message for control of H. armigera is that resistance management is essential in genetically modified crops and must be season long and area-wide to be effective. © 2016 Society of Chemical Industry.

Influência da idade do hospedeiro e da aprendizagem no comportamento quimiotáxico e no parasitismo de Trichogramma pretiosum

RESUMO Trichogramma pretiosum Riley, 1879 mantido em ovos de Ephestia kuehniella Zeller, 1879, tem sido utilizado no controle biológico de Spodoptera frugiperda (J. E. Smith, 1797). No entanto, fatores como idade do hospedeiro e experiência prévia, podem influenciar o parasitismo e o comportamento do parasitoide. Esse estudo avaliou a influência da idade dos ovos e da experiência em ovos e extrato de ovos de S. frugiperda no comportamento quimiotáxico e no parasitismo de T. pretiosum. Ovos de S. frugiperda com 24, 48 e 72 horas, foram expostos a fêmeas de T. pretiosum. Também foi avaliado o tempo de experiência do parasitoide, no mesmo hospedeiro, por 1, 3, 4, 5, 6 e 24 horas, assim como, seu tempo de exposição (1, 2, 3 e 24 horas). As respostas quimiotáxicas de T. pretiosum (experiente e não experiente) em extrato de ovos de S. frugiperda foram observadas em olfatômetro tipo Y. As taxas de parasitismo foram registradas em teste de escolha, com insetos experientes e inexperientes com ovos e extrato de ovos de S. frugiperda. O parasitismo em S. frugiperda foi significativamente maior em ovos com 24 horas de idade. Fêmeas inexperientes e experientes por 1, 3 e 4 horas, apresentaram uma menor taxa de parasitismo, quando comparadas a fêmeas expostas por 5, 6 e 24 horas. Não houve diferença de parasitismo em fêmeas expostas por 2, 3 e 24 horas, comparadas às expostas por uma hora. Fêmeas experientes foram mais atraídas ao extrato de ovos de S. frugiperda, do que ao controle (hexano). A porcentagem de parasitismo, em fêmeas inexperientes, foi maior em ovos de E. kuehniella (hospedeiro de origem), no entanto, o mesmo resultado não foi observado em fêmeas experientes.

Assessing the impact of arthropod natural enemies on crop pests at the field scale

There are many reasons why it is important that we find ways to conserve, and better utilize natural enemies of invertebrate crop pests. Currently, measures of natural enemy impact are rarely incorporated into studies that purport to examine pest control. Most studies examine pest and natural enemy presence and/or abundance and then qualitatively infer impact. While this provides useful data to address a range of ecological questions, a measure of impact is critical for guiding pest management decision-making. Often some very simple techniques can be used to obtain an estimate of natural enemy impact. We present examples of field-based studies that have used cages, barriers to restrict natural enemy or prey movement, direct observation of natural enemy attack, and sentinel prey items to estimate mortality. The measure of natural enemy impact used in each study needs to be tailored to the needs of farmers and the specific pest problems they face. For example, the magnitude of mortality attributed to natural enemies may be less important than the timing and consistency of that mortality between seasons. Tailoring impact assessments will lead to research outcomes that do not simply provide general information about how to conserve natural enemies, but how to use these natural enemies as an integral part of decision-making.

Does mating interfere in the biological characteristics of a population of Trichogramma pretiosum?

Trichogramma spp. are parasitoids used in the regulation of insect populations that can cause economic damage. In order to ensure good performance, understanding some of their biological characteristics is essential. The objective of this study is to evaluate whether mating interferes with the biological characteristics of a population of Trichogramma pretiosum collected in the field. In all experiments, groups of mated and unmated females were used. We also verified any interference from mating on the biological characteristics of the offspring. We found that mating can alter the parasitism and longevity of genitor females, in addition to changing longevity among the descendants, but once parasitized, the eggs develop normally, showing similar emergence percentage and number of offspring as those from unmated females. In addition, we verified that the population of T. pretiosum collected in the field presented individuals with reproductive thelytokous and arrhenotokous characteristics. This fact highlights the importance of careful investigation on the reproduction mode of populations collected in the field, thus avoiding problems in the effective management of insect populations.