How PICS Bags work …

Key facts about insect respiration

- Insects require oxygen

- Have high metabolic rates

Normoxia – space bag with mesh Hypoxic – space bag

UNKNOWNS

How much O2 does the cowpea bruchid consume?

Do O2 and CO2 affect feeding?

Developmental stage differences in susceptibility ?

Where do bruchids get their water?

Normoxia – space bag with mesh Hypoxic – space bag

Healthy 3rd instar bruchid larva Desiccated 2nd instar larva

Methods - Callosobruchus maculatus

2. Feeding behavior – Purdue Insect Feeding Biomonitor

3. Sealed containers – septum bottles

1. O2/CO2 concentrations – Mocon head-space analyzer

Hypoxia or Hypercarbia - FeedingCO2 alone

Hypoxia or Hypercarbia - FeedingO2 alone

O2 consumption and CO2 production

O2 consumption and CO2 production per bruchid(first instar larva till adult emergence)

Conclusions - Callosobruchus maculatus

The insect uses ~ 8-9 ml O2 during development

Drop in O2 , not rise in CO2, affects the feeding behavior

The bruchid larvae are burning carbohydrates

Role of water in combination with O2

C6H12O6 + 6O2 6CO2 + 6H2O

C6H12O6 + 6O2 6CO2 + 6H2O

What happens in a PICS bag?

• Insects infesting the grain draw down the oxygen and raise the carbon dioxide level.

• The drop in oxygen cause the insects to cease feeding and go into a state of suspended animation.

• Not feeding means not growing and developing and most important of all, not reproducing.

• Not reproducing means the population doesn’t expand, which means a serious problem never develops.

Bruchid Population Expansion – Why PICS bags work

• 1 pair of adults at start of storage• 30 days later – 50 pairs• 60 days later – 2500 pairs• 90 days later – 6,250,000 pairs

• If you arrest feeding, growth and development and reproduction in the first 60 days or so, a serious problem never develops. PICS bags do that – at low cost, simply, using bags that are durable and manufactured in Africa, without insecticides

• Bottom line – you don’t have to kill insects to control them!

Thanks especially to

• Venu Margam• Dick Shade• Ibrahim Baoua• Susan Balfe