Aspectos biológicos de Euchroma gigantea (Linnaeus, 1758) (Coleoptera: Buprestidae) em Pachira aquática Aubl. (1775) (Bombacaceae)

Abstract

Pachira aquatica Aubl. (Bombacaceae) (false-cocoa) is a tree which has been broadly used for urban arborization. In some regions of Brazil this tree is found to be infested by Euchroma gigantea (Linnaeus, 1758) (Buprestidae: Coleoptera) whose larval xylophagous habit can cause damages that may bring the fall of P. aquática trees. Considering that in three cities located on the Southeast and Central-West of Brazil, such as: São Paulo, Brasília and Goiânia), were registered serious problems related to infestation of P. aquática by E. gigantea and also because of the difficulties to conduct research using xylophagous insects, the present study was carried out to determine the duration of larval instars, to estimate adult longevity and also to find out the ratio and the sexual proportion of adults colected in the field. Insects were collected on the campus of the Universidade Federal de Alagoas (UFAL), located in the city of Maceió, Alagoas from trees which showed the infestation signals of E. gigantea and conducted to the Laboratório de Entomologia of the Natural History Museum of UFAL, where they were reared on glass cages to obtain the mass of eggs which were then placed on Petri dishes. As soon as the larvae eclose, they were fed on an artificial diet formely prepared to Diatraea flavipennella Box, 1931 (Lepidoptera: Crambidae) and pieces of P. aquática branches. The date of ecdises and death of larvae was registered. The exuviae were kept for posterior measurement of the mesothorax and cephalic capsules. The eggs showed a brownish coloration was found to be deposited in a grouped form. Descendent of adults from the second collection time (February 2009) showed the following characteristics: incubation mean period of 22, 6 (±0,22) days; mean duration of larval period from 1st to 3th instars (17, 69±0,57), (32, 46±2,75) and (41,00±3,85) days, respectively, sexual ratio of collected adults: 0,31; longevity mean of (52,5±6,07); ratio and sexual proportion of 0,2 and 1 female: 4 males. Descendent of adults from the fourth collection time (May 2009) showed the following characteristics: embrionary period: 24,70 (±0,25) days; duration of larval period from 1st to 5th instars (16,31±0,43), (37,04±0,71), (32,66±1,18), (66,37±4,70) and 72 days, respectively; longevity of (40,08±3,12); ratio and sexual proportion of 0,25 and 1 female: 3 males. In the field, it was observed females ovipositing in breaches and P. aquatica tree wounds; adults collected in the field presented the behaviour of forensic before copulation. The high mortality revealed that the artificial diet is inadequate for rearing of E. gigantea larvae. Females of E. gigantea, which are bigger than males show a higher longevity. The mean of mesothorax from 1st to 3th instars (second collection) were 1,51 (±0,007), 1,77 (±0,053) and 2,04(±0,033); from 1st to 4th instars (fourth collection) were 1,49 (±0,005), 1,92(±0,01), 2,75 (±0,062), 3,78(±0,14). The means of the cephalic capsules from 1st to 4th instar were 1,03(±0,0005), 1,46(±0,008), 2,09(±0,036) and 3,04(±0,078) showing a growth ratio of 1,43, 5th instar (3,75 and 4,0). It was observed that only two larvae of E. gigantea reached the 6th instar and they were feeding. Due to the absence of sobreposition of measurement in the cephalic capsules, it is reccomended the use of this parameter to determine the instars of E. gigantea.