Starches and Insect Control Starches affect red flour beetle development and reproduction.

Natural starch is an abundant nutrient carbohydrate (C6H10O5)n, found mainly in the seeds, fruits, tubers, roots, and stem pith of of the head capsule (to indicate stage of plants, notably in corn, potatoes, wheat, and rice, and varying larval development – instars), weight of larvae, and proportion of the widely in appearance according to source waxy corn starch (2% amy- total larvae that were alive at but commonly prepared as a white, amor- lose), corn starch (25% amy- Pest Management the observed time periods. phous, tasteless powder. Natural starch lose), wheat starch (25% On starches, development usually consists of 25% amylose (linear amylose), cross-linked wheat of larvae was adversely af- starch polymers) and 75% amylopectin starch (70% total dietary fi- fected, and larvae failed to (branched starch polymers). ber), high-amylose starch develop beyond second in- Resistant starches (RS) include (70% amylose), and potato stars. Additionally, survival on starches that are resistant to enzymatic starch (12-20% amylose). flour and flour plus yeast was hydrolysis in the small intestines of hu- The development on far superior to survival on mans. RS are classified as RS1, RS2, RS3, starches was compared with starches. (See the illustration and RS4. development on flour alone on page 53.) • RS1 refers to resistant starch that is and flour plus 5% by weight The worst larval survival encased physically by whole grains. of brewer’s yeast diet. The Dr. Bhadriraju was on potato starch, followed • RS2 is a granular resistant starch. latter diet is used in the labo- Subramanyam by wheat starch and corn • RS3 refers to non-granular, retro- ratory for mass-rearing this starch. Potato starch, which graded, or crystalline resistant starch. species. belongs to the RS2 type, is re- • RS4 is a manufactured resistant About 90% of the starch particle sizes sistant to enzyme digestion due to low starch. were below 15 to 68 microns, whereas surface-to-volume ratio of the granules Whole grains can deliver RS1, green 80% of the flour particle sizes were be- and cross-linking between molecules pro- bananas deliver RS2, and RS3 is found in vided by enriched phosphorus content ready-to-eat breakfast cereals, bread ______in these compact granules. crusts, coocked and cooled potatoes, and On starches, development of The cross-linked wheat starch and cooked and cooled pasta. RS4 is manu- 70% amylose corn starch are resistant factured from various sources, including larvae was adversely affected, to enzyme degradation, becaue their wheat, potato, and tapioca, and is avail- and larvae failed to develop be- tightly packed structure reduces enzyme able from a variety of ingredient suppli- access to the starch chains. The devel- ers. yond second instars. Addition- opment results are consistent with this finding. Red Flour Beetles ally, survival on flour and flour The adverse effects of starches on The literature has very little informa- plus yeast was far superior to growth of larvae compared to flour or tion on the effects of various starches on flour plus yeast suggest that the starches red flour beetle development and repro- survival on starches. lack certain essential nutrients for nor- duction. One study published in 1966 ______mal development. What these constitu- showed 100% mortality of larvae of the ents are at this point is unclear, but we red flour beetle, a major pest of flour mills, low 132 microns. Therefore, starch par- speculate that it could be protein compo- when they were fed potato starch. ticle sizes were smaller than that of the nents that these starches lack. In the laboratory, my graduate student, flour particles, and it is possible for lar- Xue Meng, conducted a series of experi- vae or adults of red flour beetle to con- Adult Preference Tests ments to see: sume them. In 30cm-diameter and 8cm-high are- 1. How well larvae develop on six dif- About 5g each of starch, flour, and nas, 2.5g of a starch and 2.5g of flour were ferent starches with various amylose con- flour plus yeast (5% by weight) were placed at the north and south ends. Fifty tents. transferred individually into 30-ml plas- unsexed adults of the red flour beetle were 2. Whether or not adult flour beetles tic condiment cups. Fifty red flour beetle released at the center of the arena. All are attracted to starches. eggs were added into each cup. Three arenas were checked at 36, 48, 60, and 3. If flour beetles lay eggs on starches. cups were sampled every three days. Lar- 72 hours after adult introduction to de- vae from cups were recovered. termine the number of adults retained in Development Studies Measurements were made on the fol- starch and flour. The six types of starches used included lowing aspects: length of the larvae, width These studies showed that 48-80% of

52 First Quarter 2010 MILLING JOURNAL

52_53_Subi_Column.pmd 2 2/18/2010, 11:43 AM ______the released adults were retained in starch to lay eggs. This suggested that feeding and flour in each arena. Currently, tests are underway may stimulate egg laying. The results also showed that the num- In additional tests, we observed that ber of adults retained in starches did not with different percentages of red flour beetles placed on flour and then vary significantly from those in flour, sug- protein admixed with wheat transferred to starches laid eggs. Simi- gesting that starches were as attractive as larly, beetles that failed to lay eggs on flour to the adults. starch to determine whether starches when placed on flour laid eggs protein plays an important role during the next three days, reinforcing Egg-Laying Tests that feeding on suitable substrates (flour) A pair of newly-emerged adults of flour in development, survival, and is necessary for egg laying. beetles were placed on 2.5g each of the six Currently, tests are underway with dif- starches, flour, and flour plus yeast diet in oviposition of the red flour ferent percentages of protein admixed 30-ml plastic condiment cups. Every three beetle. with wheat starch to determine whether days, the adults were sifted form the starch ______protein plays an important role in devel- or flour and moved to fresh starch or flour opment, survival, and oviposition of the diets. There were four such transfers. The age number of eggs laid ranged from 0.1 red flour beetle. number of eggs laid was counted every to three eggs per female. The low number three days ending on day 15. of eggs laid on starches suggests that trig- Bhadriraju Subramanyam (Subi) is a These results showed that on average, gers for egg laying are absent in starches. professor in the Department of Grain Sci- red flour beetle laid 97 and 109 eggs per A simple test in the laboratory showed ence and Industry at Kansas State Uni- female on flour and flour plus yeast, re- that adults placed on a sieve above flour versity, Manhattan. He can be reached at spectively, whereas on starches, the aver- do not lay eggs and need to be in the flour 785-532-4092 or [email protected]. Effect of Starch vs. Flour on Larval Development

Illustration courtesy of the Kansas State University Department of Grain Science and Industry.

MILLING JOURNAL First Quarter 2010 53

52_53_Subi_Column.pmd 3 2/18/2010, 11:44 AM