Effects of modified atmospheres on insects with special reference to silo-bags
Prof. Shlomo Navarro
Green Storage Ltd. Israel e-mail: snavarro@green-storage.co.il
October 14, 2014
Navarro - Effects of MA on insects in silo-bags
1

Modified atmospheres and hermetic storage take advantage of the basic fact that
Storage insects are aerobic organisms requiring oxygen for their survival
October 14, 2014 Navarro - Effects of MA on insects in silo-bags 2

3 October 14, 2014 Navarro - Effects of MA on insects in silo-bags

A moth larva with spiracles along the body
October 14, 2014 Navarro - Effects of MA on insects in silo-bags 4

What is hermetic storage ? hermetic storage is a type of biogenerated MA
It consists of generation of an oxygen depleted and carbon dioxide enriched interstitial atmosphere by the respiration of the living organisms in the ecological system of a sealed storage .
October 14, 2014 Navarro - Effects of MA on insects in silo-bags 5

Organisms that contribute to the generation of MAs
October 14, 2014 Navarro - Effects of MA on insects in silo-bags 6

Bio-generation of MAs in relation to the atmospheric gas composition and the humidity of their environment
Aerobic conditions
High oxygen
Low carbon dioxide
Anaerobic conditions
Low oxygen
High carbon dioxide
20
<
65% RH
15
10
Aerobic fungi, seed germ
65 to 85% RH
5
Anaerobic bacteria
>
85% RH
0
0 10 20 30 40 50 60 70 80 90 100
Carbon dioxide (%)
October 14, 2014 Navarro - Effects of MA on insects in silo-bags 7

First challenge in MA and hermetic storage
Maintaining a well sealed storage structure
October 14, 2014 Navarro - Effects of MA on insects in silo-bags 8

Day
Night
Heated air expands
October 14, 2014 Navarro - Effects of MA on insects in silo-bags
Cooled air contracts
9

Atmospheric pressure
October 14, 2014 Navarro - Effects of MA on insects in silo-bags 10

At low atmospheric pressure
At high atmospheric pressure
Inside atmosphere moves out
October 14, 2014
External atmosphere moves in
Navarro - Effects of MA on insects in silo-bags 11

Parameters to determine
GASTIGHTNESS of the structure
1- Leaks of the structure. Can be assessed using pressure test.
2- Permeability of the membrane, particularly in flexible structures. Should be measured in a laboratory.
October 14, 2014 Navarro - Effects of MA on insects in silo-bags 12

Second challenge in MA and hermetic storage
Preventing permeation of oxygen through the flexible liners
October 14, 2014 Navarro - Effects of MA on insects in silo-bags 13

Oxygen permeability requirements [mL/(m 2 24 h)] of liners in relation to various storage capacities (m 3 ) and oxygen ingress rates (%/24 h) for successful application of hermetic storage of dry grain.
O
2
ingress rate (0.15%/24h)
450
400
350
300
250
200
150
100
50
0
O
2
ingress rate (0.10%/24h)
O
2
ingress rate (0.05%/24h)
0 500 100 200 300 400
Volume of the structure (m
3
)
October 14, 2014 Navarro - Effects of MA on insects in silo-bags 14

Third challenge in MA and hermetic storage
Absorption and adsorption of carbon dioxide by the commodity
Gastight structure
Leaky structure
A – Carbon dioxide distribution
B - Exposure period
C - Aeration period
October 14, 2014
Navarro - Effects of MA on insects in silo-bags 15

Recommended ranges for variable pressure test carried out in structures destined for gaseous treatments to control storage insects.
Type of gaseous treatment
Fumigants
Controlled atmospheres
Modified atmospheres including airtight storage
October 14, 2014
Structure volume in cubic meters
Variable pressure test decay time (min) 250 to 125 Pa
Empty structure 95% Full
< 500
500 to 2,000
2,000 to 15,000 <
< 500
500 to 2,000
3
4
6
6
7
2,000 to 15,000
< 500
500 to 2,000
11
10
12
2,000 to 15,000 18
Navarro - Effects of MA on insects in silo-bags
6
5
6
3
3
4
1.5
2
9
16

Phosphine loss from an empty structure of 7.5 m 3 capacity in relation to half-life pressure decay time. Phosphine loss should not exceed 100 ppm/day.
250
225
200
175
150
125
100
75
Exposed
Shaded
50
25
0 1 2 3 4 5
Minutes for half-life pressure decay
6
October 14, 2014 17
Navarro - Effects of MA on insects in silo-bags

Fourth challenge in MA and hermetic storage
Liner durability:
1. Insect damage
2. Rodent damage
3. Weather damage, mainly UV.
4. Mechanical damage
October 14, 2014 Navarro - Effects of MA on insects in silo-bags 18

2
October 14, 2014 Navarro - Effects of MA on insects in silo-bags 19

Measured CO
2 concentration during storage time of three silo-bags with soybeans at 11.5%, 12.9% and 14.9% m.c. and average ambient temperature (adapted from Bartosik, 2008).
October 14, 2014 Navarro - Effects of MA on insects in silo-bags 20

Calculated O
2 and CO
2 concentration in silo-bags containing wheat of initial m.c. at 12, 14 and 16% w.b. for locations at Pergamino and Balcarce. Initial ס at Saenz Pe temperature 25 o C (adapted from Baretto et al., 2012)
.
October 14, 2014 Navarro - Effects of MA on insects in silo-bags 21

October 14, 2014 Navarro - Effects of MA on insects in silo-bags 22

Insect respiration
20
15
10
5
Residual oxygen within the hermetic storage
Critical point
Insect respiration
Oxygen ingress rate 0.05 %/day
0
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Weeks
October 14, 2014 Navarro - Effects of MA on insects in silo-bags 23

Modified atmosphere generated by respiration of insects in hermetic storage (calculated theoretical).
Based on grain mass containing different infestation levels of insects with an oxygen ingress ra א e of O.24%/day.
October 14, 2014 Navarro - Effects of MA on insects in silo-bags 24

Calculated weight-loss from a grain mass containing initial infestation of 2 insects/kg, at different oxygen ingress rates.
October 14, 2014 Navarro - Effects of MA on insects in silo-bags
Target gas tightness level
25

Target gas tightness to control storage insects in dry cereals, in hermetic storage structures
Daily oxygen ingress rate:
1- Below 0.05 % O
2
/day prevents oscillated oxygen concentration and increased weight loss.
2- Between 0.05 and 0.24 % O
2
/day allows oscillated oxygen concentration and increased weight loss.
October 14, 2014 Navarro - Effects of MA on insects in silo-bags 26

Conclusions
• MA or hermetic storage are very promising quality preservation and insect control technologies.
• There are a number of challenges in the application of MA or hermetic storage:
1. Maintaining a well sealed storage structure.
2. Preventing permeation of gas through the structural membrane
(by improved liners)
.
3. Consider absorption and adsorption of carbon dioxide by the commodity.
4. In flexible storages improve liner durability; to insect damage; to rodent damage; to weather; and to mechanical damage.
5. For silo-bags daily oxygen ingress rate should be below
0.10 % O
2
/day.
6. For silo-bags oxygen permeability requirements of liners should be below 400 [mL/(m 2 24 h)]
October 14, 2014 Navarro - Effects of MA on insects in silo-bags 27

Silobags for sealed storage of grain
October 14, 2014 Navarro - Effects of MA on insects in silo-bags 28