Potencial de Trichospilus diatraeae (Hymenoptera: eulophidae) para o controle de Diatraea saccharalis (Lepidoptera: crambidae) em cana-de-açúcar

Abstract

Trichospilus diatraeae Cherian & Margabandhu, 1942 (Hymenoptera: Eulophidae) is a gregarious parasitoid mainly from Lepidoptera pupae. The outcome of a biological control program from Diatraea saccharalis (Fabricius, 1794) (Lepidoptera: Crambidae) using T. diatraeae depends on laboratory and field studies. This work aimed to evaluate the potential of T. diatraeae for controlling D. saccharalis in sugar cane. This research was carried out in the Entomology Laboratory and on the Experimental Farm from Universidade da Grande Dourados (UFGD). First, the development of T. diatraeae, with different number of females from this parasitoid in D. saccharalis pupae, was studied. For this, D. saccharalis pupae were exposed to the parasitism through T. diatraeae females , on the densities of 1:1, 7:1, 14:1, 21:1, 28:1 and 35:1 (parasitoid-host), respectively. The percentage of T. diatraeae parasitism and emergence on D. saccharalis pupae was 100% respectively, in all the female densities of this parasitoid. The cicle length of T. diatraeae was 19.25 ± 0.22 days on 1:1 density and 17.00 ± 0.00 days on 35:1 density. The progeny by pupa varied from 106 ± 12.38 a 514.67 ± 54.55 offsprings by pupa, on 1:1 and 35:1 densities, respectively. The sexual ratio diminished with the density increase, varying between 0.97 ± 0.01 and 0.89 ± 0.01, on 1:1 and 35:1 densities, respectively. The percentages of T. diatraeae parasitism and emergence on D. saccharalis pupae were not influenced by the female densities of the parasitoid. The densities of 14 and 21 T. diatraeae females by D. saccharalis pupa are the ideal ones for the formation of this parasitoid on laboratory conditions. After this, the parasitism behavior of T. diatraeae on D. saccharalis pupae was evaluated on the presence of caterpillars and feces of this host in stalks of sugar cane. D. saccharalis pupae were inserted in sugar cane stalks. After pupae fixing, each stalk was put into transparent plastic bottles, on which 21 T. diatraeae females were released. On the treatment in which the caterpillars were used, two vents were made on the stalk; in one of them the pupa was inserted and on the other, the caterpillar. For the treatment with the host feces, D. saccharalis pupae was inserted and later, feces were put near the vent. T. diatraeae met and became a parasite of D. saccharalis pupae, inserting them in the sugar cane stalks. The percentage of T. diatraeae parasitism on D. saccharalis pupae was 50%; 83.33% and 16.66% when it was only used the pupa of this host; pupa and caterpillar; pupa and feces, respectively. The presence of D. saccharalis caterpillar in the stalks favored to locate the pupa of this lepdopteraeae through the parasitoid, which increased the parasitism percentage. On the last study, it was valued the number of T. diatraeae females for controlling D. saccharalis in sugar cane plants. On each plant , three stalks were sellected and a vest was made in each one to insert a D. saccharalis pupae. After pupae fixing, each plant of sugar cane was individually covered with a cage and later, 84, 168, 336, 672, 1344 and 2688 females of T. diatraeae were released, representing proportions of 28, 56, 112, 224, 448 or 896 parasitoids by pupa of D. saccharalis. T. diatraeae met and became a parasite from D. saccharalis pupae, which were alloted on the sugar cane plants. The number of D. saccharalis pupae living on T. diatraeae females presented an addition with an increase on the proportion of 28 to 56 and tended to stabilize on the other proportions. The density of 56 T. diatraeae females by D. saccharalis pupae is the designated one for the releasing of this parasitoid in commercial cultures of sugar cane, considering the methodological and environmental conditions on which this work was developed.