| Abstract |
The present investigation is conducted to examine the possibility of enhancing and / or protecting the effectiveness of two different baculoviruses (NPV and GV) inocula either by increasing the susceptibility of host insects or reducing the deterioration of virus activity under natural sunlight (UV effect ).In this respect, different natural and chemical additives were tested for their impact as well as its nature-The obtained results can be summarized in the following points :
1- The granulovirus of Agrotis segetum (AgseGV) is first time tested in, present study as a source of enhancin protein for Sp1rNPV. No enhancement effect was detected when AgseGV was incorporated at three different concentrations (3.85 x 107 , 1 x 10g and 3.85 x 10g capsule/ml diet) with SphNPV. The calculated LC50 values for the virus alone treatment of SphNPV combined with the three GV concentrations, respectively, were 7.91 x 104, 1,12 x 105, 2.13 x 105 and 2.00 x 105 PIB's/ml diet.
However, the synergistic effect was detected when AgseGV concentrations were increased to 3.16 x 109, 1 x 101° and 3.16 x lOlo capsule/ml diet. The potency values were increased from 1.008, 3.55 to 13.412, respectively at the tested respective AgseGV concentrations.
Whereas, in the case of AgseNPV the synergistic effect was detected at three concentrations 3.16 x 105, 1 x 106 and 3.16 x 106 PIB'slml diet with SphNPV. The potency values were increased from
1.31, 2.064 to 2.747, respectively, at the tested respective AgseNPV concentrations.
2- Neemazal-T(Neem), as a synergistic additive, was added at five different concentrations (1, 5, 10, 20 and 50 ppm) to the granulovirus AgseGV and tested against A. ipsilon neonate larvae. Results of the bioassay tests demonstrated that the neem oil enhanced the activity of AgseGV by reducing the LC50 values from 3.59 x 10' to 7.11 x 106 capsule/ml diet for the virus alone treatment and virus + neem at 10 ppm (5.057 fold).
The LT50 values for the last three neem alone concentrations 10, 20 and 50 ppm were 53.21, 9.39 and 3.21 days, respectively. These values were decreased from 14.13 days for the virus alone treatment to 13.14, 10.56, 7.29, 7.18 and 2.87 days for the five tested neem concentrations (1, 5, 10, 20 and 50 ppm), respectively, when incorporated with the lowest virus concentration (3.85 x 10' capsule/ml diet).
The combination also, affected larval weight of tested A. ipsilon. It reduced the average weight from 0.243376 gm/larva in the virus alone treatment (control treatment) to 0.003486 gm/larva in the combined treatment of GV + 10 ppm Neem.
3- Lignin natural products (at 1 % concentration) when tested as synergistic additives, did not give a synergistic effect on either SphNPV or AgseGV bioassayed against neonate S. littoralis or A. ipsilon larvae, respectively.
4- Fluorescent brighteaer-28 was used at three different concentrations (0.05, 0.075 and 0.1 % of diet) to increase the efficacy of both AgseGV and AgseNPV tested against A. ipsilon neonate larvae. F. brightener tested alone, did not result in larval mortality whereas, the rates of larval mortality due to virus were increased with increasing F.
brightener additive concentrations, compared to the virus alone. In case of AgseGV, the rate of enhancement was 1096.678 fold at 0.1 % concentration. Also, the LTSO value was decreased from 11.47 to 4.66 days at the concentration of 3.85 x 107 capsule/ml diet with 0.1 % F. brightener.
In the case of AgseNPV, the rate of enhancement was increased to 1.242, 68.85 and 1232.999 fold for the same abovementioned F. brightener concentrations. The calculated LT50 value (at the virus concentration of 1 x 105 PIB's/ml diet) was decreased from 44.80 days (in virus alone treatment) to 19.51, 5.91 and 5.63 days for the same abovementioned F. brightener concentrations. With the concentration of 3.16 x 105 PIB'sJml diet, the LT50 decreased from 16 days (for the virus alone treatment) to 13.0 and 6.1 days for the F. brightener concentrations at 0.05 and 0.075, respectively.
In conclusion, the combination with Neem or F. brightener additives has a synergistic effect on baculoviruses .
5- In UV-pr©tectant experiments, four lignin natural products were tested as W-protectant additives combined with SphNPV under two different sources of W radiation; simulated W and natural sunlight. The exposure times to both UV lamps and natural sunlight were 0, 4, 16, 32, 64 and 128 minutes.
LP4 (lignin product no. 4) gave significantly the best protection effect to the virus; calculated potency of 6.687 or 21.852 folds under the simulated UV or natural sunlight, respectively.
5. i- In the comparative tests between LP4, Fluorescent brightener¬28 and Mg lignosulfonate, the LP4 showed again tobe the best UV pmtectant under either simulated UV or natural sunlight (calculated potency of 27,637 or 67.161 folds, respectively). Whereas,calculated
potencies were 4.41 or 3.63 folds and 1.28 or 16.69 folds for Mg lignosulfonate and F. brightener•28, respectively
6- Three different concentrations of the LP4 (1, 5 and 10 %) were tested for virus protection evaluation. The highest LP4 concentration (10 %) gave the highest rate of protection to S. littoralis NPV. The calculated potency values for 1, 5 and 10 % of LP4 product were 3.572, 5.086 and 44.633 folds under simulated UV and 6.52, 11.31 and 498.76 folds under natural sunlight.
6.1- Based on the results of the abovementioned experiment, the LP4 product used at the three different concentrations was further tested under the natural sunlight conditions on cotton foliage in the field. The results of two trials demonstrated that the 10 % concentration of LP4 was again the best UV- protectant under the semi-field (outdoors) conditions. The calculated potencies were 1.43, 1.95 and 2.159 folds at LP4 concentrations 0.1, 0.5 and 0.9 %, respectively. At three higher LP4 concentrations 1, 5 and 10 %, the calculated potencies were 1.916, 3.653 and 151.89 folds, respectively. In conclusion, the LP4 product showed the best UV protectant for the virus treated on the cotton plant foliage under field conditions, thus prolonging the persistence of virus deposits under Egyptian sunny conditions.
7- Protectant additives ;lignin additives (LP l, LP2, LP3, LP4 and Mg lignosulfonate) tested with SpIiNPV and AgseGV at 1 % concentration had similar pH values (7.55, 7.65, 7.80, 7.50 and 7.60). whereas, synergistic Tinopal LPW additive to AgseNPV or AgseGV has a value of pH 8. The most effective protectant lignin additive was the LP4 has a value of pH 7.5 which nearly similar to that of the least effective (LP 1, LP2 and LP3; pH about 7) or Tinopal LPW (pH 8) at concentration 1 %. However, LP4 at pH 5.10 was the most effective protectant than Mg
lignosulfonate (pH 5.05) at 10 % concentration. It is difficult to state that the pH value of lignin additive played a key role in protecting the virus.
8- Using the spectrophotometer, all lignin additives (LP 1, LP2, LP3 and LP4) showed a high rate of UV- absorption (from 210-900 nm), especially in the very effective UV region of the inactivation 300-320 nm at concentrations 1 °lo and 10 %.
9- Electronmicrograph (TElv>) of polyhedra combined with the lignin additive indicated the possibility of physical protection of the polyhedra crystal by the additive The latter appeared to surround the poiyhedra with a continuous layer which was visible in the dark field examination.
|