Laboratory studies were conducted to verify the influence of photophase on diapause incidence in the Neotropical brown stink bug, Euschistus heros (Fabr., 1798), fed with soybean [Glycine max (L.)] Merrill pods. Nymphs were maintained at three different photophases: 10 h, 12 h, and 14 h, with constant temperature of 25 +/- 1 degree C and relative humidity of 65 +/- 5%. With 14 h, approximately 100% of the adults showed mature reproductive organs; the shoulder (spine) length was significantly greater (2.96 and 2.79 mm for females and males, respectively) than those of bugs maintained at the photophase of 12 h (2.60 mm for females and males) and 10 h (2.59 and 2.53 mm for females and males). At the longer photophase (14 h), E. heros showed better reproductive performance and greater feeding activity than insects reared at 10 h and 12 h; in all photophases bugs tended to reduce feeding from the 1st to the 6th week of life. Body color was considered an unreliable parameter to indicate diapause incidence. However, at 14 h, 60% of the insects were dark brown and 40% were reddish brown. These results indicate that E. heros enters reproductive diapause with photophase of 12 hours or less, showing immature reproductive organs or with intermediate development, with shoulder (spine) less developed and reduced feeding activity.
, during one year, to evaluate the diapause incidence and the occurrence of different seasonal morphs. The majority of the insects (ca. 90%) with mature reproductive organs was observed during the summer (December-March), when E. heros was found on soybean or on sunflower; in the beginning of autumn, most insects (87%) showed immature reproductive organs, and they were found on star bristle and under fallen leaves. Bugs with mature reproductive organs had more developed shoulders (3.23 and 3.27 mm, for males and females, respectively) than bugs with immature organs (2.91 and 2.89 mm, for males and females, respectively). Two distinct body colors, dark brown and reddish brown, were observed. Nevertheless, the reddish brown was the predominant color of both mature and immature adults during all year. Adults were parasitized by Hexacladia smithii (Ashmead) (Hymenoptera: Encyrtidae) and Tachinidae mainly Trichopoda giacomellii (Blanchard) (Diptera: Tachinidae) (80% and 40% of parasitism in male and female, respectively) during summer (December), when the bugs colonized sunflower. In soybean, 12% of males and 10% of females were parasitized, whereas in fallen leaves, the parasitism rate was 5% in both sexes.These results showed that in autumn/winter (shorter photoperiod) the majority of the insects were inactive under fallen leaves, showing immature reproductive organs and less developed shoulders, indicating that, at this time, these bugs were in diapause.
Foram desenvolvidos estudos em laboratório com o percevejo-marrom Euschistus heros (Fabr.) para se determinar o estágio fotossensível à indução da diapausa. Utilizaram-se duas combinações de fotoperíodo 10L: 14E e 14L: 10E mantendo-se constante a temperatura em 25 ± 1ºC e a umidade relativa em 65 ± 5%. Fases distintas do desenvolvimento dos insetos foram submetidas às combinações fotoperiódicas, com os seguintes tratamentos: T1 = 10L: 14E (ovo-adulto); T2 = 14L: 10E (ovo) e 10L: 14E (1º ínstar-adulto); T3 = 14L: 10E (ovo-1º ínstar) e 10L: 14E (2º ínstar-adulto); T4 = 14L: 10E (ovo-2º ínstar) e 10L: 14E (3º ínstar-adulto); T5 = 14L: 10E (ovo-3º ínstar) e 10L: 14E (4º ínstar-adulto); e T6 = 14L: 10E (ovo-4º ínstar) e 10L: 14E (5º ínstar-adulto). Sob fotoperíodo de dias curtos, de ovo a adulto (T1), o tempo de incubação dos ovos foi maior (6,1 dias) do que o observado nos demais tratamentos (5,3 a 5,6 dias). O tempo total de desenvolvimento foi maior (35,5 dias) para insetos submetidos a fotoperíodo de dias curtos, a partir do ovo (T1), do 1º ínstar (T2), do 2º ínstar (T3) ou do 4º ínstar (T4), do que para os insetos sob fotoperíodo de dias curtos a partir do 4º (T5) ou 5º ínstar (T6; cerca de 32,0 dias). A mortalidade total foi maior (56,7%) para os insetos que permaneceram sob fotoperíodo de dias curtos, de ovo a adulto (T1), do que para aqueles nos demais tratamentos (26,7 a 45,0%). Insetos submetidos ao fotoperíodo de dias curtos, a partir do ovo (T1), 1º ínstar (T2), 2º ínstar (T3) ou 3º ínstar (T4) apresentaram de 84,8% a 100% dos indivíduos em diapausa. A partir do tratamento com fotoperíodo longo, até o 3º ínstar (T5), não ocorreu mais diapausa. Esses resultados demonstram que a fotossensibilidade de E. heros inicia-se nos primeiros estágios de desenvolvimento, e que se acentua a partir do 3º ínstar.
-Laboratory studies were conducted on mating, ovipositional rhythm, and fecundity of the southern green stink bug, Nezara viridula (L.) fed on immature fruits of privet, Ligustrum lucidum Thunb. and soybean, Glycine max (L.) Merrill. A greater number of pairs were observed mating on privet (27 to 37 %) than on soybean (22 to 23 %). The preoviposition period was significantly shorter when females fed on privet (15.5 days) than when they fed on soybean (23.9 days). The intervals of time between the first four ovipositions, and between the 1st and the 4th oviposition were shorter on privet than on soybean (range of 1.9 to 3.3 days less on the former food). Greater percentage of females N. viridula oviposited and showed greater fecundity on privet than on soybean. On privet, the oviposition rhythm peaked at days 11 and 17; however, no peaks on oviposition were observed on soybean.
Laboratory and field studies indicated that privet, Ligustrum lucidum (Oleaceae), is an important host plant of the neotropical stink bug, Loxa deducta (Walker) (Hemiptera: Pentatomidae) in northern Paraná state. Survivorship of nymphs was high (82.9%) when fed immature fruits of privet. Nymph developmental time (from the 2nd stadium to adult) lasted <FONT FACE=Symbol>»</FONT> 49 d. At adult emergence, females attained greater (199.5 mg) fresh body weight than males (180.0 mg). Survivorship of adult L. deducta decreased gradually with time. Mean total longevity was <FONT FACE=Symbol>»</FONT> 62 d for females and <FONT FACE=Symbol>»</FONT> 55 d for males. Of 30 females observed, 25 (83.3%) oviposited when fed fruits of privet. The preoviposition period was 13.9 (± 0.51) d; fecundity was 17.8 (± 1.60) egg masses/female, and 236.0 (± 21.98) eggs/female; egg hatchability was 65.0 (± 6.48)%. Considering the total period of 4-wks, the percentage increase in fresh body weight was <FONT FACE=Symbol>»</FONT> 70% for females, and <FONT FACE=Symbol>»</FONT> 45% for males. During summer months (December to February), relatively low numbers of insects were collected on privet. During March, nymph and adult populations increased reaching a peak during April, and decreasing in May at the end of autumn. This tendency continued throughout winter (June-July-August), reaching almost zero in September at the beginning of spring, and increasing somewhat again in October-November.
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