The legs of grasshoppers are complex structures that provide the grasshopper with a variety of grips as well as a surface for stable launches and landings. The grasshopper in the picture below is resting on a blade of grass. Note that the middle (mesothoracic) leg of the grasshopper is gripping the leaf with the pad area of its tarsus, not with the claw that is on the tip. For areas where traction is good, the pads provide enough friction for grip and walking. If the grasshopper is engaged in a steep climb or on a slick surface, the claw can be engaged.
A close up of the tarsus, the most distal section of the grasshopper leg, is in the inset. The tarsus has a series of pads and ends with a claw at the tip of the leg. The pads provide an expanded surface area and can cushion the force of the leg. Inside the pads are hemolymph and air sacs. When the grasshopper lands, the air inside the sac can compress to absorb some of the shock of landing. Dampening the force with the air sac allows the grasshopper to stick to the surface where it lands. Without the air sac, landing might deform the cuticle which could then spring back and “bounce” the grasshopper off the surface. The legs of grasshoppers are under study as models for robots with legs.
Grasshopper rests on grass
Inset: Grasshopper leg with claw and tarsal pads
Photo: Lyle Buss
The Japanese cockroach, Periplaneta japonica
, has been living in New York City for over a year. Its identity was recently confirmed and reported in the Journal of Economic Entomology. The report generated a lot of media attention and idle speculation such as, Is it a super roach that will take over the city?
Periplaneta japonica is more cold tolerant than other pest cockroach species, which allows it to live outdoors in the winter. However, cockroaches are typically only considered pests when they live indoors and infest human buildings. The cold hardiness is unlikely to give them an advantage over German cockroaches where it counts: the indoor environment.
Periplaneta japonica can be a pest of food establishments and is capable of living indoors. However, its reproductive rate is slow compared to the German cockroach, the most important indoor cockroach pest in the Big Apple. Periplaneta japonica is unlikely to displace the German cockroach as #1.
The best line from a Periplaneta japonica report:
The likelihood that the new species will mate with the locals to create a hybrid super-roach is slim.
Interestingly, this quote is based on lack of fundamental knowledge that:
A) Periplaneta japonica is a different species from the other cockroaches found in NYC.
B) Distinct Species, by definition are populations that do not inter-mate and produce viable offspring.
The idea that Periplaneta japonica could be the start of interbreeding that would create a super roach is floated to titillate the imagination of the public not to inform the public. This is why I have never been a reporter.
Early in their evolution, the animals lost the ability to synthesize for themselves amino acids that are readily obtained from their diet. These amino acids are called the “essential amino acids”. Humans require 9 essential amino acids and these we must obtain from our diet. Most insects require 10. The dependence on diet for essential amino acids can limit the ability of insects to exploit some potential sources of food.
Plant saps (xylem and phloem) contain sufficient energy to support the develop of insects, but the balance of nutrients is poor and lacking in critical amino acids. Insects such as cicadas and spittle bugs that feed on plant sap have bacteria symbionts that fill the essential amino acid gap in the diet. Early in the evolution of sap feeding insects in the order Hemiptera, associations between insects and symbionts developed. The ancestors of spittle bugs, cicadas, treehoppers and leafhoppers (the Auchenorrhyncha) developed an association with symbionts of the genus Sulcia. Situated in the gut of insects, Sulcia has many of its nutrients supplied by its host and the food of its host. Other nutrients are supplied by additional host symbionts. Over time, Sulcia has lost many of the genes for biosynthesis of nutrients important for free living bacteria but some genes are strictly conserved. Throughout the Auchenorrhyncha, Sulcia has maintained the genes for biosynthesis of 8 of the 10 essential amino acids. Neither the insect nor the Sulcia could survive without these. Two of the essential amino acid pathways, histidine and methionine, were lost by Sulcia early in the evolution of the Auchenorrhyncha and that gap must be covered by an additional symbiont.
The symbionts that contribute histidine vary within the Auchenorrhyncha. However, closely related groups of within the Auchenorrhyncha share closely related symbionts. Gene sequencing of these symbionts provides evidence of the evolution within these groups. The phylogenetic trees (family trees) for these bacteria symbionts mirror the phylogenetic trees of the Auchenorrhyncha. For over 200 million years, this group of sap feeders has evolved together with its bacterial symbionts. Neither alone could exploit plant sap as a food resource, but together their relationships have been successful.
Corn Rootworm Larva
Genetically modified crops to control insect pests have both advantages and disadvantages. The most commonly deployed insect control genes express proteins from the bacteria Bacillus thuringiensis
. The proteins specifically target insects and have little effect on humans or mammals. The proteins work by interacting with receptors present in the digestive system of insects but are absent in humans and mammals. The proteins are so specific that some will target caterpillars, but not flies or beetles. Others target some beetles, but not all beetles or other groups of insects. In humans and non-susceptible animals, most BT proteins are either metabolized to release amino acids or pass through the digestive system. For non-susceptible animals, the BT proteins are one more protein in the complex mix of proteins present in any food. The largest impact on human health and safety is due to GMO crops replacing more harmful insecticides, especially the cholinesterase inhibiting insecticides that are a risk for human health and safety.
Disadvantages of the GMO crops center around resistance to the BT proteins. Insect populations that are exposed to insecticides on a consistent basis have been known to develop resistance. If a substantial portion of the pest population is no longer controlled by a BT protein, then that BT protein is lost as a control factor forever. Other concerns about BT proteins center around potential unknown effects on humans.
The BT genes and protein are present in commodities such as corn that is sold in the market. These are easily detected. Corn containing BT must be registered in order to be sold in a country. Regulation of GMO corn sales is not unified. Each country or region (as in the case of the European Union) has its own regulations that must be met by grain marketers. A new level of commodity tracking and separate storage may be required for exporters. Problems sometimes occur when a BT approved in one country is mixed in a grain shipment to a country where the BT is not approved and the shipment is rejected. Rejected shipments must be redirected to other markets that will accept the commodity which adds extra shipping costs.
2013 has been a year of record corn harvest in the US Midwest and also in some markets such as China. With bountiful domestic supply China has tightened control of BT corn shipments. The GMO corn designated MIR 162 is pending approval in China, but not yet approved. This has resulted in rejection of corn shipments at great cost to the shippers and potential disruption of the corn market.
Obviously, corn marketers would like the rules to be simple and uniform. The world may agree on unified regulations as food supply is outpaced by increased demand. However, food acceptability has a strong cultural component. In a multicultural world, uniformity is not always possible. A fragmented market creates many opportunities for niche marketing of crops targeted to meet the regulations of a specific market. Those crop producers and markers who can meet the standards can be paid a price premium. The use of GMO crops for insect control will continue to be complicated by market regulations as well as challenges posed by insect populations.
Photo: P Waring, AfricanMoths.com
There is much interest in edible insects as a food for the growing population. The list of edible insects is often based on ethnological data from native cultures that have a tradition of eating insects. The list is not always correct and may require further investigation. Some Nigerian cultures consume pupae of African silk moths from the genus Anaphe.
This practice was correlated with a seasonal disorder that causes ataxia. Patients exhibit acute deficiency of the vitamin, thiamin. Supplemental thiamin is therapeutic, reversing the symptoms of the disorder.
A group of Japanese scientists* investigated one of the silk moth species, Anaphe venata and found that the caterpillars contain a thiaminase enzyme that degrades thiamin. They found that the enzyme was heat stabile and cooking the caterpillars would not inactivate the enzyme. The scientists noted that thiaminases are found in some Australian plants eaten by Australian Aborigines. The Aborigines remove the thiaminases by washing the plant before consuming it. Unfortunately, washing the caterpillars or pupae did not remove the thiaminase. The scientists tried several methods of removing the thiaminase from the caterpillars of Anaphe venata without success. Consumption of these species is not advisable.
Interestingly, the role of the thiaminase in the silk moth larvae and pupae is unknown.
* Takahiro Nishimune, Yoshihiro Watanabe, Hideki Okazaki, and Hiromu Akai. Thiamin Is Decomposed Due to Anaphe spp. Entomophagy in Seasonal Ataxia Patients in Nigeria. J. Nutr. June 1, 2000 vol. 130 no. 6 1625-1628
Insects can be appreciated and investigated from many points of view. Interest in insects as a future food source is high because human population increases will require more production and new sources of food. Nutritionists are interested in insects as food value and bring a reductionist approach. Rumpold & Schlüter
* have published a review of the nutritional compositions of 236 edible insect species. Their compilation allows for comparison of nutritional quality that can inform decisions on what insects are the best sources of energy, protein, minerals and vitamins. The animal and human diets of the future may contain blends of insect derived nutrients.
Rumpold & Schlüter found wide variation in nutrient content but were able to make some generalizations. Most insects store energy as fat, not carbohydrate and use proteins for a variety of structural and metabolic functions. The energy content is primarily from proteins and lipids. Lipids and proteins are relatively energy dense compared to carbohydrates giving insects a high caloric value relative to their weight. Almost 80 percent of edible insects measured have caloric content above 400 kcal/100 g and 41 percent are above 500 kcal/100 g. The caloric value of insects is high even relative to meat.
Insects can feed on a variety of foods that are not edible by humans or our livestock. Raising insects on otherwise inedible food is one way to utilize more of the available biomass for human nutrition. Basic studies of nutrient content combined with innovative processing methods will lead to new foods of the future.
*Birgit A. Rumpold, Oliver K. Schlüter. 2013. Nutritional composition and safety aspects of edible insects. Molecular Nutrition & Food Research
Volume 57, Issue 5, pages 802–823.
Oriental Fruit Fly, Bactrocera dorsalis
Photo: Scott Bauer, USDA-ARS
The true fruit flies of the Genus Bactrocera
, are important pests of fruits with a global distribution. Flies in this genus (as well as important Tephritid flies in other genera such as the Medfly) are attracted to the chemical methyl eugenol. Verghese and colleagues* provide and interesting historical note on the development of methyl eugenol as a lure for Bactrocera
The discovery of methyl eugenol starts with an entomologist working in India: Frank Howlett and an observation: many Bactrocera flies were attracted to citronella. He learned from the literature of the day that the ingredients were citronellal, atral, citronellal and geraniol. However, none of these chemicals were attractive. Several months later, Howlett discovered that the list of chemicals was only partial and worked through a more complete list that contained methyl eugenol. Numerous experiments showed that only methyl eugenol, of all the components was attractive.
Howlett at first thought methyl eugenol might be a female produced pheromone because only the males were attracted. However, crushed females failed to attract male flies. Subsequent investigations have established that methyl eugenol is a food attractant for the male flies. Today, methyl eugenol continues to be an important lure and has some potential for use in pest control.
*Frank Milburn Howlett (1877–1920): discoverer of the Pied Piper’s lure for the fruit flies. Abraham Verghese, T. N. Shivananda, P. D. Kamala Jayanthi and K. Sreedevi. CURRENT SCIENCE, VOL. 105, NO. 2, 25 JULY 2013