Revista Brasileira de Entomologia
Print version ISSN 0085-5626
BORASCHI, Daniele; PERUQUETTI, Rui Carlos and DEL LAMA, Marco Antônio. Biology, social behavior and sex-allocation of Digelasinus diversipes (Kirby, 1882) (Hymenoptera, Argidae). Rev. Bras. entomol. [online]. 2005, vol.49, n.2, pp. 253-263. ISSN 0085-5626. http://dx.doi.org/10.1590/S0085-56262005000200010.
The results of a two-year study of the Neotropical sawfly Digelasinus diversipes are presented. This species is univoltine and common in Estação Ecológica Jataí, a nature reserve of Cerrado vegetation in São Paulo State, Brazil. The larvae feed gregariously on Eugenia glazioviana (Kiaersk.) D. Legrand (Myrtaceae) from November through April. Fusions of different feeding groups were frequent. After the feeding period, larvae congregate and communally construct a cocoon mass (105 cocoons ± 60SD; n = 25) attached to the trunk of the host plant, entering in diapause as prepupae until the beginning of the rainy season in October. The population peak was in December when 62% (n = 2,967) of adult emergence occurred. In experimental conditions, emergence was observed from 6:30 a.m. until 15:00 p.m., but 73.5% (n = 223) of the adults appeared between 9:00 a.m. and 12:00 h. Sex sequence was not observed during emergence but, in a single cocoon mass, males may appear 20 to 40 days earlier than females. After emergence, males may either (1) disperse (early and late in the emergence period; October and November, January and February, respectively) or (2) remain on or near the cocoon mass and mate with newly emerged females (during the emergence peak in December). Copulation lasts 4.28 minutes (±3.4SD; n = 28), and during the day, males may mate with different females (1-8; n = 5); however, females mate only once. Newly emerged females have a mean of 76 mature eggs (± 21SD; n = 19) and oviposited all of them underneath of a single leaf of the host plant. Egg guarding by females lasted only 2 (n = 12) of the 30 days of egg incubation. The female's behavioral repertoire against potential enemies was shorter than that reported for some other sawfly species. Apparently, the female induces necrosis of the leaf tissue that covers the eggs, which forms a hard shelter for the eggs during incubation. Both sexes of D. diversipes do not feed as adults (controlled condition) and have a short life span (5.2 days ± 1.7SD; minimum 1, maximum 11; n = 179). The mean sex ratio was 2.83 (± 0.014SE) in favor of females. Main mortality factors were development defects, lack of food due to intense herbivory, and attack of parasitoids. Parasitoids reared, Lymeon dieloceri (Costa Lima, 1937) (Ichneumonidae), Conura (Spilochalcis) sp. (Chalcididae) and Perilampus sp. (Perilampidae).
Keywords : Gregarious feeding; maternal care; Neotropical sawfly; sex ratio; subsocial insect.