Photosynthetic Response of Soybean to Twospotted Spider Mite (Acari: Tetranychydae) Injury

The twospotted spider mite Tetranychus urticae Koch is a common pest on soybean plants. To clarify plantarthropod interaction on mite-soybean system, leaf fluorescence, photosynthetic responses to variable carbon dioxide levels, and chlorophyll content were evaluated. Significant photosynthetic rate reduction was observed due to stomatal limitation. Stomatal closure was the major plant physiological response. As a consequence, there was reduction in photosynthetic rates. Surprisingly, plants did not show chlorophyll content reduction associated with photosynthetic impairment. No differences in fluorescence data indicate that T. urticae injury did not impair the function of light harvesting and photoelectron transport. These results showed that T. urticae could be a serious pest of soybean even on lower infestation, at least when photosynthesis was determinant to yield

Características biológicas e capacidade de parasitismo de Trichogramma pretiosum Riley (Hymenoptera, Trichogrammatidae) em ovos de Spodoptera frugiperda (J. E. Smith) (Lepidóptera, Noctuidae)

This study aimed at evaluating the biological characteristics and the capacity of parasitism of a Trichogramma pretiosum Riley, 1869 (Hymenoptera, Trichogrammatidae) strain (T. pretiosum RV) collected in Rio Verde County, State of Goiás, Brazil. The study was carried out on eggs of Spodoptera frugiperda (J. E. Smith, 1797) (Lepidoptera, Noctuidae) and conducted under controlled environmental conditions at different constant temperatures. The biological parameters determined were: developmental time (egg-adult; days); emergence (%); sex ratio; number of progeny/egg; number of generation/year; thermal constant (K); temperature threshold (Tb); daily number of parasitized eggs; cumulative parasitism (%); total number of eggs parasitized by T. pretiosum; and female longevity. To study the T. pretiosum parasitism capacity, 20 S. frugiperda eggs (< 24 h old) were placed into 8.0 cm x 2.0 cm glass vials containing one female (< 24 h old) each. Trials were carried out in a completely randomized experimental design, with 20 replications at each temperature. The environmental chambers (BOD type) were set at 18ºC, 20ºC, 22ºC, 25ºC, 28ºC and 32ºC &plusmn; 1ºC, 70 &plusmn;10% relative humidity, and 14/10 h (L:D) photoperiod. The eggs of S. frugiperda were replaced daily until parasitoid death. Results have shown an inverse correlation between developmental time and temperature, with statistically significant differences among means, except at 25ºC and 28ºC (10 days). Parasitoid emergence (%) was also influenced by temperature. The lowest percent emergence was observed at 32ºC, and the highest ones at 18ºC and 20ºC temperatures. The temperature did not affect T. pretiosum sex ratio and number of parasitoids per egg, thus allowing changes in the temperature to control insect mass production in the laboratory to meet the needs for field releases.O objetivo deste estudo foi avaliar as características biológicas e a capacidade de parasitismo de uma linhagem de Trichogramma pretiosum Riley, 1869 (Hymenoptera, Trichogrammatidae), coletada em Rio Verde, Goiás, Brasil (T. pretiosum RV). O estudo foi feito com ovos de Spodoptera frugiperda (J. E. Smith) (Lepidóptera, Noctuidae) e conduzido sob condições ambientais controladas e em diferentes temperaturas constantes. Os parâmetros biológicos determinados foram: período de desenvolvimento (ovo-adulto; dias); emergência (%); razão sexual; número de progênie/ovo; número de gerações/ano; constante térmica (K); temperatura base (Tb); número de ovos parasitados diariamente; parasitismo acumulado (%); número total de ovos parasitados por fêmea de T. pretiosum; e longevidade das fêmeas. Para estudar a capacidade de parasitismo de T. pretiosum, 20 ovos de S. frugiperda (< 24 h de idade) foram colocados em tubos de vidro (8,0 x 2,0 cm) contendo uma fêmea (< 24 h de idade) cada. Os experimentos foram conduzidos em delineamento experimental inteiramente casualizado, com 20 repetições por temperatura. As BODs foram reguladas para temperaturas constantes de 18ºC, 20ºC, 22ºC, 25ºC, 28ºC e 32ºC, umidade relativa de 70 &plusmn;10% e fotoperíodo de 14/10 h (L:E). Os ovos de S. frugiperda foram substituídos diariamente até a morte do parasitóide. Os resultados mostraram uma relação inversa entre o tempo de desenvolvimento e a temperatura, com médias apresentado diferenças estatisticamente significativas entre si, com exceção das temperaturas de 25ºC e 28ºC (10 dias). A emergência do parasitóide (%) também foi influenciada pela temperatura. A menor porcentagem de emergência foi observada a 32ºC e a maior nas temperaturas de 18ºC e 20ºC. A temperatura não alterou a razão sexual nem o número de parasitóides por ovo, permitindo mudanças na temperatura para controlar a produção de insetos em laboratório, com o fim de atender às necessidades das liberações no campo

Biological control as part of the soybean Integrated Pest Management (IPM) : potential and challenges

Soybean production is usually performed on large scales, requiring simple but efficient pest management to be successful. Soybean fields are inhabited by several species of arthropods, demanding constant development of management practices to prevent pest outbreaks. More recently, stink bugs have become the most important pest group of soybeans in the Neotropics, responsible for up to 60% of the applied insecticides in Brazil. Natural enemies represent an important mortality factor that can keep the damage caused by stink bugs below the economic threshold levels without additional control actions. Thus, Conservation Biological Control (CBC) strategies can be adopted to preserve or even promote the increase in such natural enemies in the fields, or alternatively, massive releases of biocontrol agents in Augmentative Biological Control (ABC) programs could be adopted. Simple practices such as reducing insecticide use (with the adoption of economic thresholds), prioritizing harmless insecticides or biopesticides, and planting resistant soybean cultivars have been adopted in Brazil with positive results. The challenges to increasing the adoption of more complex stink bug management in commodity crops such as soybean may be overcome using the more recent economic incentives in the global agenda of decarbonized agriculture. The potential and challenges of conservation and augmentative biological control are further discussed in this review

Effect of increasing rate of insecticides on its selectivity for Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae)

The present study evaluated the effect of different rates of chlorantraniliprole, chlorantraniliprole + lambda-cyhalothrin, spinosad, and chlorfenapyr on their selectivity for the pupae and adults of Trichogramma pretiosum. The negative effect of majority of the insecticides tested on most of the parasitoids was directly proportional to the rate of the insecticide applied. Chlorantraniliprole at a rate of 10 g a.i. ha-1 was classified as harmless (class 1) to both pupae and adults of the parasitoid. The effect of chlorantraniliprole at a rate of 20 to 50 g a.i. ha-1 varied from harmless (class 1) to slightly harmful (class 2) to the adults of T. pretiosum. Chlorantraniliprole 10 + lambda-cyhalothrin at 5 g a.i. ha-1 was classified as harmless (class 1) to the pupae and moderately harmful (class 3) to the adults of T. pretiosum. On the contrary, the highest rate of chlorantraniliprole 50 + lambda-cyhalothrin tested (i.e., 25 g a.i. ha-1) was classified as slightly harmful (class 2) to the pupae and harmful (class 4) to the adults of the parasitoid. Similarly, increasing the application rate of spinosad and chlorfenapyr also exhibited an increase in toxicity. Spinosad at a rate of 24 g a.i. ha-1 was classified as slightly harmful (class 2) and harmless (class 1) to the pupae and adults of T. pretiosum, respectively. Spinosad at 96 g a.i. ha-1 was classified as both moderately harmful (class 3) and harmful (class 4) to the pupae of the parasitoid. Chlorfenapyr at a rate of 192 g a.i. ha-1 was classified as both slightly harmful (class 2) and moderately harmful (class 3) to the pupae of T. pretiosum, whereas chlorfenapyr at 336 g a.i. ha-1 was categorized as slightly harmful (class 3) and harmful (class 4) to the pupae. These results indicate that an increase in the rate of insecticide affected T. pretiosum negatively. Therefore, higher insecticide rates should only be adopted when strictly necessary to control the target pest, because they might compromise the biological pest control process in the field