Abstract
Cotesia flavipes (Cameron, 1891) (Hymenoptera) is a gregarious endoparasitoid used in applied biological control against Diatraea saccharalis (Fabricius, 1794) (Lepidoptera). In this study, we characterize the larval external morphology and the number of instars of C. flavipes. Parasitized larvae of D. saccharalis were sampled from the 1st to the 10th day after parasitism and dissected in an anticoagulant buffer for collection of C. flavipes immatures. Immatures were processed for scanning electron microscopy. Larvae of C. flavipes were prepared in NaOH solution and slide mounted to allow for mandible size measurements. Analysis of measurements of the parasitoid larval mandible size indicated that C. flavipes has three instars. Newly hatched larvae are caudate-mandibulate, assuming a hymenopteriform shape later in their development. The anal vesicle began to expand in the first instar and, once expanded, remained unchanged up to the beginning of the third instar. At the third instar, the anal vesicle decreased in volume. Herein we report the development and possible functions of the larval external structures modified during the development of C. flavipes, as for example their role in aiding newly-eclosed larvae to avoid the host immune response and to move within the host. To summarize the morphological changes during parasitoid growth, we should mention that the modifications in the anal vesicle were correlated with the feeding activity, and the maintenance of the anal vesicle indicates that this structure remained functional, probably playing a role in nutrient absorption and host regulation. On the other hand, the mandibles of early stage larvae are probably used to assist the parasitoid larvae during eclosion.
Highlights
Immature parasitoids develop in only one host, from which they obtain their nutritional requirements and, in some cases, the physical support to develop (DEBACH & ROSEN 1991, GRENIER 1997)
Cotesia flavipes (Cameron, 1891) is one example of a natural enemy that is used in extensive areas in many Brazilian states to control the most common pest of sugarcane, the sugarcane borer Diatraea saccharalis (Fabricius, 1794) (Lepidoptera: Crambidae) (BOTELHO & MACEDO 2002)
General descriptions of the external morphology are available for several braconids (HAGEN 1964, FINLAYSON 1987, FISCHER et al 2006, 2008), there is no detailed description of the morphology of the immature of C. flavipes throughout its development
Summary
Larvae of D. saccharalis were reared on an artificial diet based on soybean meal and wheat germ (PARRA & MIHSFELDT 1992), under controlled conditions (26 ± 1°C; 60 ± 10% RH; 14 h photophase), following PARRA (1999). Adults of C. flavipes were fed with a 10% honey solution (v/v) and kept inside plastic Petri dishes (65 x 22 mm). Parasitized larvae were kept in plastic Petri dishes (90 x 14 mm) containing artificial diet and were sampled daily until parasitoid egression. Host larvae were dissected in an anticoagulant buffer (98 mM NaOH, 0.19 M NaCl, 1.7 mM EDTA, 41 mM citric acid, pH 4.5) (STRAND et al 1997), and immature parasitoids were collected for further analysis. Larvae of C. flavipes were collected daily from at least five parasitized hosts and pooled in groups of one-hundred larvae, carefully washed three times in the anticoagulant buffer, and immersed in 1% NaOH solution (w/v). The time of exposure to the NaOH solution varied according to the status of larval development. The terminology used in the description of the immature stages of C. flavipes followed that of HAGEN (1964) and FISCHER et al (2008)
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