Euborellia annulipes (LUCAS) (DERMAPTERA: ANISOLABIDIDAE) A COTTON BOLL WEEVIL PREDATOR: AGE-DEPENDENT FECUNDITY WITH AN ARTIFICIAL DIET F.S. Ramalho1, W.P. Lemos1, and J.C. Zanuncio2. (1) Unidade de Controle Biológico (UCB)/Embrapa Algodão, Caixa Postal 174, 58107-720, Campina Grande, Paraíba, Brazil. Bolsista do CNPq. e-mail:
[email protected], (2) Departamento de Biologia Animal, Universidade Federal de Viçosa, Minas Gerais. ABSTRACT Few informations regarding the biology and ecology of dermapteran predators has been reported. For possibile use of Euborellia annulipes (Lucas)(Anisolabididae) in biological control programs against the cotton boll weevil Anthonomus grandis Boheman (Curculionidae) it is essential to know the effects of temperature on the reproductive attributes of adult females of this predator. Our objective was to evaluate the reproductive potentiality of females of E. annulipes under laboratory conditions using an artificial diet, at 25 and 30oC. Fecundity began to decline at the 84th d at 25oC and 74th d at 30oC of adult age and ended with the death of the females at both temperatures. Females of E. annulipes oviposited an average of 206.2 and 306.0 eggs, and had a mean longevity of 198.4 and 149.1 d at 25 and 30oC, respectively. The relationship between age-specific fecundity and age was described by a model composed of a linear function for the increase in fecundity at early ages combined with a exponential function for the subsequent decreaee in egg laying at older ages. This relationship was described by f(x)= αx exp(-βx). In the model f(x) is the daily age-specific fecundity rate (eggs/female/day), x is the age in days (age class), and α and β are constants. Age class 1 (0 to 20 days as adults). The model was fitted to the data by non–linear least square technique (SAS Institute Inc. 2000), weighted by the number of females contributing to the means giving the curves in Fig. 4. The parameters α (± s.e.) and β (± e.s.) respectively were estimated to be at 25oC (1.599 ± 0.256 and 0.356 ± 0.033) and at 30oC (3.226 ± 0.581 and 0.415 ± 0.044). The model described 78.8% and 74.8% of the variation at 25 and 30o C, respectively. The pattern in age-specific fecundity was the same at all two temperatures. INTRODUCTION The cotton boll weevil (Anthonomus grandis Boheman) (Curculionidae) is the most important pest of cotton in several countries that produce this crop (Ramalho 1994). The most common method used by cotton farmers to control populations of A. grandis is intense and continuous applications of insecticides. However, the utilization of insecticides results in negative impacts on the agroecosystems, specially on the beneficial fauna and the environment. Dermapterans are organisms with high predatory capacity (Mourier 1986). They are voracious, have high attack capacity and have been important in the control of several insect pests, particularly, coleopterans (Klostermeyer 1942). Although the biology of few representatives of the order Dermaptera has been studied, primarily because most are native of tropical areas where resources required for research are quite limited, E. annulipes has been the subject of several investigations in different parts of the world. In Brazil, during the last few years there has been an increase in the knowledge on this predator, especially its biology and rearing techniques (Lemos et al. 2001), impact of temperature on development (Lemos et al. 1998), and thermal requirements (Lemos et al. 1999). This research was designed to to evaluate the reproductive potential of E. annulipes under laboratory conditions using an artificial diet, at 25 and 30oC.
MATERIAL AND METHODS The research was conducted at the Unidade de Controle Biológico (UCB) - Embrapa Algodão, Campina Grande, Paraíba, Brazil. The predator was maintained in growth chambers, type BOD, at 25 and 30oC, relative humidity of 60 ± 10%, and photoperiod of 14:10 (L:D) h. The E. annulipes studied were from a colony (12th generation) maintained at UCB, as described by Lemos et al (1999). Oviposition Periods and Fecundity. A total of 20 (at 25oC) and 18 (at 30oC) newly-emerged pairs of adult E. annulipes were selected for each temperature and confined in Petri dishes (9.0 x 1.5 cm) until the death of females. A male which died before its female partner were replaced. Each Petri dish had a container (3.5 x 0.5 cm) with 460 mg of artificial diet (Lemos et al. 1998) which was changed every 2 d. Half of the top and bottom and sides of the Petri dishes were covered with black paper providing light and dark environments. This was done because dermapterans are nocturnal, and light conditions are important for mating activity of these insects (Shepard et al. 1973). Two pieces of absorbent paper (11.5 x 10.0 cm) bent in four identical parts, creating a specific site for oviposition of E. annulipes, were placed in the dark areas of each Petri dish, along side 1 ml of distilled water. Whenever necessary, an additional 0.3 ml of water was added to each dish to maintain constant humidity. Every 10 d, the papers inside the Petri dishes were changed and 1 ml of distilled water was added. Number of dead adults were daily observed, as were number of clutches deposited per each female, number of eggs per clutch per female, and number of eggs per female of E. annulipes. RESULTS AND DISCUSSION Population Models. The relationship between age-specific fecundity and age was described by a model composed of a linear function for the increase in fecundity at early ages combined with a exponential function for the subsequent decreaee in egg laying at older ages. This relationship was described by f(x)= αx exp(-βx). In the model f(x) is the daily age-specific fecundity rate (eggs/female/day), x is the age in days (age class), and α and β are constants. Age class 1 (0 to 20 days as adults). The model was fitted to the data by non–linear least square technique (SAS Institute Inc. 2000), weighted by the number of females contributing to the means giving the curves in Fig. 1. The parameters α (± s.e.) and β (± e.s.) respectively were estimated to be at 25oC (1.599 ± 0.256 and 0.356 ± 0.033) and at 30oC (3.226 ± 0.581 and 0.415 ± 0.044). The model described 78.8% and 74.8% da variation at 25 and 30o C, respectively. The pattern in age-specific fecundity was the same at all two temperatures. A similar pattern in age-specific fecundity was seen when Macrolophus caliginosus Wagner (Heteroptera: Miridae) was fed on various stages of Tetranychus urticae Koch (Acari: Tetranychidae) (Hansen et al. 1999). As temperature increased, the time required to reach maximum rate of oviposition decreased, and the highest fecundity rate was predicted to be attained at 30oC. Artificial Diet. In our study the predator was maintained on artificial diet in the laboratory, based on powder milk, beer yeast, chicken food, and bran (Lemos et al. 1998). Neiswander (1944) and Bharadwaj (1966) fed this predator on a combination of animal and vegetable foods. It remains to be investigated whether newly-emerged adults of E. annulipes, when released in field conditions to control cotton boll weevil populations, maintain or even increase their rates of survival and/or reproductive capacity once they feed on their natural prey. De Clercq and Degheele (1993a,b) and Cohen (2000) reported that some predator species (Heteroptera: Pentatomidae) maintained several generations on artificial diets or unnatural prey in laboratory environments maintained their biological qualities as indicated by search time, handling time, amount extracted, and extraction rates. According Chocorosqui and De Clercq (1999) predation rates of P. maculiventris (Say) reared on artificial diet were similar or somewhat higher than those of predators reared on live prey. In their research, nymphs and adults of Podisus nigrispinus (Say) reared for three and four generations, respectively, on artificial diet were able to prey on Anticarsia gemmatalis (Hübner) (Noctuidae) both under laboratory and greenhouse
conditions. De Clercq and Degheele (1993a) also found that prolonged rearing (> 15 generations) on artificial diet did not affect the predation capacity of nymphs and adults of P. maculiventris and P. nigrispinus. Similarly, after prolonged maintenance of Geocoris punctipes Say bugs on artificial diet, their predation capacity was identical to that of their field-collected prey (Hagler and Cohen 1991, Cohen 2000). It is expected that weight besides reproductive and predation capacity of adults of E. annulipes from nymphs reared on artificial should be similar to those fed on natural prey and that in field conditions these predators should have the same efficiency against populations of A. grandis grandis. Thus, the availability of an artificial diet that supports growth and reproduction of E. annulipes provides a means for mass rearing procedures of this predator for use in integrated management programs of cotton boll weevil.
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Figure 1. Observed (dots) and predicted (solid line model) age-specific fecundity (eggs/female/day) of E. annulipes fed on artificial diet as a function of female adult age. Age class 1 (0 to 20 days as adults).
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