Adeney de Freitas Bueno

Effects of pesticides used in soybean crops to the egg parasitoid Trichogramma pretiosum

This research aimed to study the effects of different insecticides, herbicides and fungicides on eggs, larvae and pupae of Trichogramma pretiosum. The results showed that studied pesticides had different impact on T. pretiosum. Esfenvalerate 7.5 and spinosad 24.0 grams ha-1 were classified as harmfull (class 4) while clorfluazuron 10.0, methoxyfenozide 19.2, lactofen 165.0, fomesafen 250.0, fluazifop 125.0, glyphosate 960.0 (Gliz® and Roundup Transorb®), azoxistrobin + ciproconazol 60.0 + 24.0, azoxistrobin 50.0 and myclobutanil 125.0 grams ha-1 were chemicals classified as harmless to all imature T. pretiosum stages. All the other chemicals evaluated had different impact on T. pretiosum being classified from harmless (class 1) to harmful (class 4) varying the impact accordingly to the different parasitoid stage. Then, less noxious products should be chosen whenever possible to be used in a soybean IPM program.

Biology and thermal requirements of Telenomus remus reared on fall armyworm Spodoptera frugiperda eggs

This research aimed at studing Telenomus remus Nixon biology reared on Spodoptera frugiperda (J.E. Smith) eggs at different temperatures. Based on the development of the cycle (egg-adult), the thermal requirements and the number of parasitoid generations at constant temperatures were determined. Initially, 24-hour-old S. frugiperda eggs were submitted to parasitism by T. remus during 5 h, being then transferred to acclimatized chambers regulated at 15, 20, 25, 28, 31, and 35°C. The cycle (egg to adult) was influenced by temperature varying from 8.3±0.01 to 47.2±0.01 for females and 8.1±0.01 to 46.8±0.01 days for males at 31 and 15°C, respectively. The emergency (%) was also influenced by temperature. A reduction in emergency was observed at 15°C and no emergency at 35°C. T. remus sex ratio was not influenced by temperature. Sexual rate was not changed by temperature. Regarding to thermal requirements, thermal constant (K) and inferior thermal threshold (Tb) were higher for T. remus females (158.88 degree-days and 12.5°C) when compared to males (154.12 degree-days and 12.6°C). The estimated number of T. remus generation per year for males and females at laboratory conditions was 5.6 and 5.6, 16.9 and 17.3, 28.3 and 29.0, 35.1 and 36.0, 39.6 and 40.7 at 15, 20, 25, 28, and 31oC, respectively.

Oviposição, desenvolvimento e reprodução de Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) em diferentes hospedeiros de importância econômica

The host selection for oviposition by Spodoptera frugiperda (J.E. Smith) among corn, millet, cotton and soybean, and its relationship with the biological characteristics were investigated. Free and non-choice tests for oviposition using plots containing five plants each, from each host in plastic greenhouse, resulted in similar oviposition preference among the host plants. In addition, selected biological characteristics of S. frugiperda were determined in the laboratory with larvae feeding on host leaves, and the combination of leaf and cotton boll. Neonate larvae exhibited low success of colonization on cotton boll compared to the leaves of all other hosts. Spodoptera frugiperda fed only on cotton bolls exhibited longer larval and pupal development, and longer adult life span; however with similar egg production. Larvae fed cotton leaves during six days and then transferred to cotton bolls, however, exhibited development and reproduction similar to those reared on corn or only on cotton leaves. Therefore, the variations on immature stages of S. frugiperda were not related with host selection for oviposition which was similar among the studied hosts. Based on our data, the millet as a winter, rotational, and cover crop is a potential host for S. frugiperda, while leaves and cotton bolls were diets of intermediate suitability as compared to corn and soybean leaves.

Parasitism capacity of Telenomus remus Nixon (Hymenoptera: Scelionidae) on Spodoptera frugiperda (Smith) (Lepidoptera: Noctuidae) eggs

This work studied the parasitism capacity of Telenomus remus Nixon (Hymenoptera: Scelionidae) on Spodoptera frugiperda (Smith) (Hymenoptera: Scelionidae) eggs at 15, 20, 25, 28, 31, and 35°C, aiming to use this natural enemy in biological control programs in crops where S. frugiperda was considered pest. The parasitism during the first 24 h was 60.90, 81.65, 121.05, 117.55 and 108.55 parasited eggs per female from egg masses of approximately 150 eggs, at 15, 20, 25, 28 and 31°C, respectively. Females of T. remus reached parasitism higher than 80% at 15, 20, 25, 28 and 31oC at 5, 27, 8, 2, and 2 days, respectively. At 35oC, there was no parasitism. The highest parasitism rates occurred at 20, 25, 28 and 31°C. T. remus female longevity varied from 15.7 to 7.7 days from 15 to 31°C. The highest tested temperature (35°C) was inappropriate for T. remus development. At that temperature, female longevity was greatly reduced (1.7±0.02) and egg viability was null. All T. remus survival curves were of type I, which showed an increase in mortality rate with time.

Seletividade de diferentes agrotóxicos usados na cultura da soja ao parasitoide de ovos Telenomus remus

Biological control agent preservation is crucial to the integrated pest management success. However, chemical control is yet useful for crop production. Thus, pesticide selectivity to beneficial insects is a feature that must always be taken into account in order to choose the best chemical. Therefore, this research studied the impact caused by different pesticides in the egg parasitoid, Telenomus remus Nixon (Hymenoptera: Scelionidae) emergence, when sprayed on the larvae and pupae stage (Egg masses from 100 to 150 eggs of Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) six and ten days after the parasitism, respectively). Three trials, with 11 treatments and 5 repetitions, were carried out in the laboratory with insecticides, fungicides and herbicides. Each test was carried out with 10 treatments of chemicals and water as control. All chemicals were tested at rates used in soybean crops. Eggs of S. frugiperda parasitized by T. remus, were immersed in the treatments for five seconds. After completely dry, they were placed in plastic bags until the emergence of adults of parasitoids. The viability of parasitism was evaluated and the reduction in the emergence of the parasitoids classified according to the rules of the International Organization for Biological Control (IOBC). The results showed that the insect growth-regulating (IGR) insecticides flufenoxuron, diflubenzuron, methoxyfenozide as well as the insecticides imidacloprid + beta-cyfluthrin and acephate were harmless to the parasitoid immature stages . Spinosad was classified as harmless for larvae of T. remus. Gama-cyhalothrin was slightly harmful to larvae and harmless to pupa of T. remus. Bifenthrin and chlorpyrifos were, respectively, slightly harmful and harmful to both stages of development of T. remus development. Regarding to the tested herbicides, 2,4-D, s-metolachlor, flumioxazin, paraquat dichloride + diuron, paraquat dichloride and glyphosate (Roundup Transorb®) were harmless. However, glyphosate + imazethapyr, clomazone, glyphosate (Gliz®), glyphosate (Roundup Ready®) were harmless to the larvae stage and slightly harmful (class 2) to T. remus pupae. Similar results were obtained with the fungicides flutriafol + tiofanate, carbenzadin, tebuconazol + trifloxystrobin and azoxystrobin + ciproconazol which were classified as harmless. Tiofanate-metil, tebuconazol and epoxyconazol + pyraclostrobin were slightly harmful to larvae and pupae. Inversely, epoxyconazol and azoxystrobin were harmless to larvae and slightly harmful to pupae. Flutriafol was classified as slightly harmful to both development stages of T. remus.

Trichogramma pretiosum (Hymenoptera: Trichogrammatidae) Parasitism of Trichoplusia ni (Lepidoptera: Noctuidae) Eggs Under Different Temperatures

ABSTRACT A study of the biological characteristics and thermal requirements of the parasitoid Trichogramma pretiosum Riley, 1879 (Hymenoptera: Trichogrammatidae) on eggs of Trichoplusia ni (Hübner, 1802) (Lepidoptera: Noctuidae) at several different temperatures was performed in this work. Eggs of T. ni were exposed to T. pretiosum strain Tspd parasitism for 5 hr and then transferred to environmentally controlled growth chambers set at the temperatures of 18, 21, 24, 27, 30, and 33 ± 1°C. The duration of the T. pretiosum egg-to-adult period was affected by temperature, varying from 6 to 18 d over the range of the studied temperatures. The number of individuals emerged per egg and the sex ratio also were affected by temperature variations, but regression analysis did not find correlation between the increase of temperature and the observed variation of these biological parameters. Similarly, parasitism viability (percentage) was influenced by temperature variation, but always exceeded 80% at all tested temperatures. The thermal lower limit of development (Tbase) and the thermal constant (K) for T. pretiosum were 11.84°C and 128.37 DD, respectively. These results here reported indicate that T. pretiosum was impacted by the temperature, however, this parasitoid had a satisfactory performance on T. ni eggs at all studied temperature (from 18 to 33°C), showing potential to be used successfully as a biological control agent of this pest in different regions that fit in this tested temperature range. Also, the rearing temperature of this parasitoid might be changed from 18 to 33°C, according to commercial demands for accelerating or retarding mass production for field releases without damages to the parasitoid development.

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 pla ntarthropod interaction on mite-soybean system, leaf fluorescence, photosynthetic responses to variable carbon dioxide levels, and chlorophyll content were evalua ted. Significant photosynthetic rate reduction was observed due to stomatal limitation. Stomatal closure was the ma jor plant physiological response. As a consequence, there was reduction in photosynthetic rates. Surprisingly, pl ants did not show chlorophyll content reduction ass ociated with photosynthetic impairment. No differences in fluore scence data indicate that T. urticae injury did not impair the function of light harvesting and photoelectron tran sport. These results showed that T. urticae could b e a serious pest of soybean even on lower infestation, at least when photosynthesis was determinant to yield.

Host preference of the egg parasitoids Telenomus remus and Trichogramma pretiosum in laboratory

Host preference of the egg parasitoids Telenomus remus and Trichogramma pretiosum in laboratory. This research aimed to evaluate the host preference of the egg parasitoids Telenomus remus and Trichogramma pretiosum. Trials were carried out in laboratory, under controlled environmental conditions (25 ± 2oC temperature; 70 ± 10% RH; and 14 h photophase). The parasitoid searching behavior was evaluated based on the distribution (%) of eggs parasitized by each parasitoid, on egg masses of each host species. Results showed the host preference of T. remus by Spodoptera cosmioides eggs. T. pretiosum, reared in A. gemmatalis eggs, choose to parasitize always eggs of the host where the parasitoid had been reared. The egg preference was not observed when T. pretiosum was reared in S. frugiperda eggs. These results show that, in general, host preference of T. remus is less influenced by the host where it is developed than T. pretiosum. Host preference is an important parameter for biological control programs because more than one pest species may occur in the field, different from those where they were reared in the laboratory.

Biological characteristics and parasitism capacity of Trichogramma pretiosum Riley (Hymenoptera, Trichogrammatidae) on eggs of Spodoptera frugiperda (J. E. Smith) (Lepidoptera, 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 Goias, 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 ± 1oC, 70 ±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.

Preferência hospedeira do parasitoide de ovos Trichogramma pretiosum

The success of Trichogramma spp. releases in biological control programs relies upon the knowledge of the parasitoid bio-ecological characteristics and the parasitoid interaction with the target pest. Therefore, this research aimed to evaluate T. pretiosum host preference among eggs of S. frugiperda, S. albula, S. eridania, A. gemmatalis, P. includens, D. saccharalis and A. kuehniella. Polyethylene cages were set to test host preference of T. pretiosum comparing each two groups of host species. The evaluated parameter was parasitism (%) and parasitoid emergence (%). T. pretiosum females parasitized preferably A. kuehniella eggs. However, in the bioassay with A. gemmatalis X P. includens and D. saccharalis X S. frugiperda there was no difference in the parasitism. Then, in the free choice test, in the absence of the host in which the parasitoid was reared (A. kuehniella), T. pretiosum shows no host preference indicating the existence of pre-imaginal conditioning acquired during larval development. The parasitism viability results were variable among the different tested hosts.