Diceraeus melacanthus (Dallas) (Hemiptera: Pentatomidae) development, preference for feeding and oviposition related to different food sources

ABSTRACT The dispersion of Diceraeus melacanthus (Dallas) from soybean (first crop season) to maize (second crop season) is facilitated by the presence of weeds (e.g. Commelina benghalensis) and soybean grains on the ground. Understanding insect development and behavior on different food sources is important to develop pest management strategies. Thus, three independent experiments were conducted to study D. melacanthus nymph development, and adult preference for feeding and oviposition in different food source scenarios in the field. The first two trials studied development and food preference of D. melacanthus related to different food sources (C. benghalensis branches, moistened soybean grain + soybean seedlings, maize seedlings + C. benghalensis branches, moistened soybean grains + maize seedlings, moistened soybean grains + C. benghalensis branches, maize seedlings, as well as a standard diet). The third trial evaluated D. melacanthus oviposition preferences between the aforementioned plants. Overall, moistened soybean grains resulted in better nutritional quality, thus being crucial for D. melacanthus development, triggering faster nymph development as well as better overall adult fitness. The combination of soybean grains and maize seedlings or C. benghalensis branches showed great potential to benefit D. melacanthus, since these complementary food sources improved stink bug fitness, increasing mainly adult longevity, fecundity and egg viability. Therefore, it can be concluded that in order to reduce D. melacanthus outbreaks in second season maize, it is important to reduce soybean harvest loss (reducing, therefore, moistened soybean grain on the ground) and eliminate stink bug associated plants like C. benghalensis.

Effects of parasitoid and host age on the parasitism of Trichogramma pretiosum on eggs of Anticarsia gemmatalis

Abstract The ages of parasitoid females and their hosts can have substantial effects on parasitism and parasitoid efficacy. This relationship has been investigated over the last few decades and found to vary among species. To our knowledge, it was virtually unknown for Trichogramma pretiosum wasps that parasitize Anticarsia gemmatalis eggs. Therefore, the influence of parasitoid and host age on the parasitism of T. pretiosum on eggs of A. gemmatalis was here evaluated in three independent bioassays. Neither the number of parasitized eggs nor that of emerged parasitoids differed between T. pretiosum females of different age. The number of parasitoids per egg and the sex ratio were higher for 5-day-old females. Regarding host age, the number of parasitized eggs was highest for A. gemmatalis eggs aged 24 h (9.60), followed by eggs aged 48 h (1.00), while no parasitism was observed for eggs aged 72 h. The number of parasitoids per egg and sex ratio were not influenced by host age. Preference was significantly higher for host eggs aged 24 h (79.67%), followed by eggs aged 48 h (16.99%) and 72 h (3.33%). Accordingly to these results, the key challenge for a successful T. pretiosum release to control A. gemmatalis in the field is to synchronize the presence of up to 5-day-old adults with the most susceptible phase of the host eggs (1 day).

Influence of host preference, mating, and release density on the parasitism of Telenomus remus (Nixon) (Hymenoptera, Platygastridae)

ABSTRACT We evaluated the influence of host preference, mating, and release density on Telenomus remus (Nixon, 1937) (Hymenoptera: Platygastridae) parasitizing eggs of Spodoptera frugiperda (Smith, 1797) (Lepidoptera: Noctuidae). First, we tested host preference of T. remus (free choice test) offered a choice between eggs of Corcyra cephalonica (Stainton, 1865) (Lepidoptera: Pyralidae) and S. frugiperda. Parasitism capacity and host preference (S. frugiperda) of T. remus reared on either of the two hosts did not differ. Secondly, we evaluated the influence of mating behavior of T. remus females on its parasitism. Only the offspring sex ratio differed between treatments, indicating that the species reproduces by parthenogenesis of the arrhenotoky type. Finally, we evaluated the influence of release density on T. remus parasitism. This was tested by releasing different numbers of the parasitoid per S. frugiperda egg using T. remus reared for different numbers of generations on C. cephalonica eggs. The regression analysis between percentage of parasitism and density of released T. remus females showed a quadratic effect for all tested parasitoid generations (F35, F40, and F45) with maximum parasitism from 65.07% to 71.69%. Our results allow the conclusion that (a) T. remus prefers S. frugiperda eggs, regardless of the host on which this parasitoid was reared, showing no preimaginal conditioning; (b) Mating does not affect the number of eggs parasitized by T. remus or the development of its offspring; and (c) The optimal T. remus release density when reared on C. cephalonica is between 0.133 and 0.150 females/S. frugiperda.

Larval development of Spodoptera eridania and Spodoptera frugiperda fed on fresh ear of field corn expressing the Bt proteins (Cry1F and Cry1F + Cry1A.105 + Cry2Ab2) / Desenvolvimento larval de Spodoptera eridania e Spodoptera frugiperda alimentadas com espigas de milho verde expressando proteínas Bt (Cry1F e Cry1F + Cry1A.105 + Cry2Ab2)

ABSTRACT: The objective of this study was to evaluate extent of larval period, larval survival (%), food consumption, and pupal biomass of Spodoptera eridania and Spodoptera frugiperda (Lepidoptera: Noctuidae ) fed on fresh ears of field corn expressing Bt proteins (Cry1F and Cry1F+Cry1A.105+Cry2Ab2). Larvae of Spodoptera spp. survived less than two days when they consumed Bt corncobs and showed 100% mortality. Spodoptera eridania reared on non-Bt corn cobs showed higher larval development (21.6 days) than S. frugiperda (18.4 days) and lower viability (56.4% and 80.2% for S. eridania and S. frugiperda , respectively). A higher amount of corn grains was consumed by S. eridania (5.4g) than by S. frugiperda (3.9g). In summary, this study demonstrated that the toxins Cry1F and Cry1F + Cry1A.105 + Cry2Ab2 expressed in fresh corn cobs contributed to protect ears of corn against S. frugiperda and the non-target pest S. eridania . However, itis important to monitor non-Bt cornfields because of the potential of both species to cause damage to ear sof corn.

RESUMO: Este estudo teve como objetivo avaliar o período de desenvolvimento larval, sobrevivência larval (%), consumo de alimento e biomassa pupalde Spodoptera eridania e Spodoptera frugiperda (Lepidoptera: Noctuidae ), alimentadas com grãos verdes de milho Bt que expressam as proteínas Cry1F e Cry1F + Cry1A.105 + Cry2Ab2). As larvas de Spodoptera spp. alimentadas com milho Bt sobreviveram por até dois dias, registrando-se 100% de mortalidade. A espécie S. eridania alimentada com grãos de milho não Bt apresentou um maior desenvolvimento larval (21,6 dias) do que S. frugiperda (18,4 dias), e menor viabilidade larval (56,4% e 80,2% para S. eridania e S. frugiperda respectivamente). Uma maior taxa de consumo de grãos foi observada para S. eridania (5,4g) do que para S. frugiperda (3,9g). Em síntese, este estudo comprova que as toxinas Cry1F e Cry1F + Cry1A.105 Cry2Ab2 expressas em grãos imaturos de milho contribuem na proteção das espigas de milho contra S. frugiperda e a praga não-alvo S. eridania , entretanto, é importante monitorar as lavouras cultivadas com milho não Bt, devido o potencial de ambas as espécies em ocasionar danos nas espigas da planta.

Aspectos biológicos de Dichelops melacanthus em três temperaturas, alimentados com grãos imaturos de milho 2B688Hx e 2B688 / Biological aspects of Dichelops melacanthus at three temperature, reared on immature 2B688Hx and 2B688 corn grains

RESUMO: Este estudo investigou os aspectos biológicos de Dichelops melacanthus (Hemiptera: Pentatomidae) em três temperaturas (19±1°C, 25±1°C e 31±1°C), alimentados com grãos imaturos de milho 2B688Hx (expressa a proteína inseticida Cry1F, para o controle de lepidópteros-alvo) e 2B688. Foi observado que a temperatura de 19±1°C prejudicou o desenvolvimento de D. melacanthus, pois, nessa condição, foi registrada a maior taxa de mortalidade das ninfas, menor peso de adultos e as fêmeas não ovipositaram. Por outro lado, a duração da fase jovem, mortalidade, peso de adultos, fecundidade e viabilidade de ovos não diferiu entre as temperaturas 25±1°C e 31±1°C. Também foi demonstrado que os aspectos biológicos dos percevejos alimentados com grãos imaturos de milho 2B688Hx não diferiram dos que se desenvolveram com a isolinha 2B688. Este estudo comprova que D. melacanthus desenvolve-se melhor em condições de temperaturas mais elevadas (até 31±1°C), e o fato de se alimentar com grãos imaturos de milho 2B688Hx não afeta o seu desenvolvimento.

ABSTRACT: This study investigated the development of Dichelops melacanthus (Hemiptera: Pentatomidae) at different temperatures (19±1°C, 25±1°C and 31±1°C) reared on 2B688Hx (expressing Cry1F insectice protein to control lepidopterans target) immature corn grains. The temperature of 19±1°C impaired the development of D. melacanthus and recorded the highest mortality of nymphs, lower weight and adult females laid no eggs. Moreover, the length of the nymphal biology, adult weight, fecundity and viability of eggs did not differ between temperatures 25±1°C and 31±1°C. It was also shown that the biological aspects of green belly stink bugs fed with 2B688Hx immature grains of corn do not differ from that develop with 2B688 isoline. This study showed that the biological cycle of D. melacanthus is favored at warmer temperature (until 31±1°C), and the consume of immature corn grain 2B688Hx does not affect its development.

Larval development of Spodoptera eridania (Cramer) fed on leaves of Bt maize expressing Cry1F and Cry1F + Cry1A.105 + Cry2Ab2 proteins and its non-Bt isoline

This study aimed to evaluate, in controlled laboratory conditions (temperature of 25±2 °C, relative humidity of 60±10%, and 14/10 h L/D photoperiod), the larval development of Spodoptera eridania (Cramer, 1784) (Lepidoptera, Noctuidae) fed with leaves of Bt maize expressing Cry1F and Cry1F + Cry1A.105 + Cry2Ab2 insecticide proteins and its non-Bt isoline. Maize leaves triggered 100% of mortality on S. eridania larvae independently of being Bt or non-Bt plants. However, it was observed that in overall Bt maize (expressing a single or pyramided protein) slightly affects the larval development of S. eridania, even under reduced leaf consumption. Therefore, these results showed that Cry1F and Cry1F + Cry1A.105 + Cry2Ab2 can affect the larval development of S. eridania, although it is not a target pest of this plant; however, more research is needed to better understand this evidence. Finally, this study confirms that non-Bt maize leaves are unsuitable food source to S. eridania larvae, suggesting that they are not a potential pest in maize fields.