| Main results |
1. The study results showed that: 28 pests belonging to 16 families and 7 orders were recorded on Cruciferae inside the greenhouse in Hanoi. Of these, 25 were of the uncovered greenhouse, 18 of the covered greenhouse. The number of nature enemies of the outside of, uncovered and covered greenhouse were 41, 35 and 21 respectively. Spodoptera litura, Pieris rapae, Plutella xylostella, Brevicoryne brassicae, Phyllostreta striolata, Micraspis discolor, Menochilus sexmaculatus, Lemnia biplagiata, Propylea japonica, Paederus fuscipes, Episyrphus balteatus, Apanteles sp., Diaeretiella rapae were presented both the inside and the outside.
2. On the cabbages and the kohlrabi, inside the greenhouse, from March 2012 to March 2013, the density of 5 pests reached two peaks. They were Spodoptera litura with 2.06-3.4 individual/m2 in May and November; Plutella xylostella (2.20-2.65, May and February); Pieris rapae (5.8-14.4, May and January); Phyllostreta striolata (4.6-18.4, May and December); and Brevicoryne brassicae (16.8-50.9, May and February). The density of natural enemy groups was extremely low. As lady-bug group, it reached two density peaks with 1.27-2.00 individual/ m2 in May and December; the others such as assasin-bug, earwing, beetle, wing-pad only got one density peak; 0.8 in June, 0.43 in October, 2.50 in February, and 1.90 in April, respectively. The parasitic bee group trivially played roles to control the density of bugs. This group only reached for 0.22% in the density peak in February.
3. On the vegetables, inside the greenhouse, assassin bugs, earwings, wing-pads, running-legs, and lady-bugs with thei preys (main pests on the vegetable) had a low correlation coefficient (R), a low desnsity, their appearance without consecutively (scattered), and their role was very low to control number of pests (as mentioned above). Two species Cotesia plutellae and Diaeretiella rapae played a active role to control number of Plutella xylostell and Brevicoryne brassicae with R =0.68-0.72. From this studies, it is able to propose that: we can exploit two species (Cotesia plutellae and Diaeretiella rapae) to control two pests (Plutella xylostella, Brevicoryne brassicae).
4. Insect populations outside the greenhouse appeared and developped without the same time of that of those populations inside the covered greenhourse. The inside, there were cultivate seasons, regular fetilizing, techniques of the cultivation were differently with that the outside. These effected the mean density of Spodoptera litura, Pieris rapae, Phyllostreta striolata, lady-bugs, assassin-bugs, wing-pads, and beetles on the cabbages and the kohlrabi. The inside of the greenhouse, the density of pests, with spraying 2 time/crop, was more high than that the outside (4-5 times/crop). The density of the species belonging to the assassin-bug group, running-legs, wing-pads, lady-bugs was also low both the inside and the outside into sprayed fields. If the spray, however, was 2 times the inside of the greenhouse and 3 times the outside of, the densty of such groups was insignificantly different.
5. In the conditional laboratory, mass rearing of Menochilus sexmaculatus and Coccinella transversalis with their food as Aphis craccivora (reared according to the process) showed that: their fecundity was high in generation 1 and 2 (55,77-79,53,96 eggs/female), and the rate of hatch was also high (71,45-87,88%). Mass rearing of E. Annulipes, with its food as the mash for cat, in plastic boxs, gave the rearing coefficient 5.6-8.1 times (on averaged: 121,5-194,9 individuals from 15-35 couple initialy. Meanwhile, with rearing in the plastic basin, that was 7,8-9,3 times (on averaged: 241,2-465,7 individuals from 30-50 couple initialy). Mass rearing of 2 species S. falleni and S.croceovittatus, with their food as S. litura and larvae of C. cephalonica, C. fuscipennis with the food as larvae of C. cephalonica gave the rate of mass rearing 17-19 individual with one couple initialy.
6. The inside of the covered greenhouse, the release of Trichogramma japonicum with a density of 740.000 individuals/ha, in June 2013, showed that: the rate of parasitism to Plutella xylostella was quite high (73,43-83,33%). That of Coccinella transversalis with a density of 1 individual/ha, in November 2012, reduced the density of Brevicoryne brassicae in duration of 6 days in comparison with control expariments. That of earwings with a density of 1 individual/m2, on the cabbage, was not able to control the density of Brevicoryne brassicae and Plutella xylostella. That of assasin bugs with a density of 0.5 individual/m2 also reduced the density of some pests (Lepidoptera) in comparison with control expariments.
7. To control pestinsects as the way of the GAP, the inside of the greenhouse, it should release one time of earwings and assassin bugs in February; red eyes bees, earwings and assasin bugs in May; and two time of lady bugs in December. 
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