Sex trap tame devastating African armyworm

The African armyworm, scientifically known as Spodoptera exempta, is a particularly devastating pest. An early warn­ing sys­tem using traps that fake the smell of mat­ing fe­male moths has de­livered a break­through in coun­ter­ing the spread of the army­worm, which can move into an area and dev­ast­ate en­tire crops.

The over 2 mil­lion farm­ers in Kenya and Tan­zania who to­gether grow over 7 mil­lion hec­tares of cer­eal, mainly maize, now say cases of army­worm in­va­sion have dwindled greatly thanks to the early de­tec­tion under a pro­ject de­veloped by the Centre for Ag­ri­cul­ture and Bios­ciences In­ter­na­tional (CABI).

The African army­worm, sci­en­tific­ally known as Spod­op­tera ex­empta, is a par­tic­u­larly dev­ast­at­ing pest. Large num­bers of the vo­ra­cious black cater­pil­lars ap­pear sud­denly, leav­ing crops and pas­ture dev­ast­ated in their wake. Once the food has been ex­hausted in one area, they mi­grate to their next des­tin­a­tion. With out­breaks are dif­fi­cult to pre­dict, they catch farm­ers un­aware and un­pre­pared. If un­con­trolled, they can cause total crop loss, with mil­lions of hec­tares af­fected in bad years.

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But un­der­stand­ing the in­sect has as­sisted sci­ent­ists in pre­dict­ing which areas might ex­per­i­ence out­breaks, some two weeks ahead of ac­tual in­va­sions. However, while such fore­casts are use­ful for na­tional plan­ning, they are of little or no value to in­di­vidual farm­ers. Gov­ern­ments often have in­suf­fi­cient ca­pa­city for timely con­trol, with in­sect­icides con­tinu­ously being ruled out due to their pro­hib­it­ive cost and dam­age to the en­vir­on­ment.

The pro­ject has there­fore put in place local re­ac­tion and mon­it­or­ing sys­tems.

Early de­tec­tion is being achieved using fact­ory en­hanced fe­male hor­mones, com­monly known as pher­omones, which act as a trap that dupes the male of the pres­ence of a fe­male ready to mate. A pher­omone is a bio­lo­gical chem­ical secreted by fe­male in­sects or even mam­mals that trig­gers the at­trac­tion of a male to a fe­male.

In the army­worm it is the basic in­dic­ator used by male moths to identify fe­male moths for mat­ing with doc­u­mented evid­ence show­ing that male army­worm moths are able to de­tect the scent of the pher­omone from a ra­dius of 10 km, de­pend­ing on wind dir­ec­tion.

The pher­omone trap also con­tains an in­sect­icide and once in­side the trap the moths die. The farm­ers then count the dead ones after every week.

Ac­cord­ing to sci­ent­ists, more than 30 catches of the moths in a week is a clear warn­ing of a pos­sible in­va­sion of army­worms. When this hap­pens, an alert is is­sued by word of mouth in schools, chiefs’ meet­ings, churches and on com­munity radio.

The pro­ject, which was pi­loted in Tan­zania sev­eral years ago and even­tu­ally scaled up in other coun­tries, has also in­volved the train­ing of farm­ers who in turn train oth­ers within the vil­lage.

Ini­tially, the plan was to train at least 200 vil­lages, but the pro­ject has ex­ceeded ex­pect­a­tion with Malawi and Tan­zania alone ex­ceed­ing the tar­get. Ac­cord­ing to Jon Knight, an eco­nom­ist from the Im­per­ial Col­lege of Lon­don who has been among the people in­volved in the ven­ture, the fore­cast­ing has been highly ef­fect­ive given the low costs in­volved.

The ini­tial cost of train­ing each vil­lage was just $233 dol­lars with an ad­di­tional $4 being used to buy the trap which lasts for up to ten years and the pher­omone cost­ing $2 a year. However, the cost has been fur­ther re­duced through more cost ef­fect­ive train­ing, and has de­livered added be­ne­fits in teach­ing re­search­ers how best to en­gage with local farm­ers.

The second phase of the pro­ject in­volves the es­tab­lish­ment and ex­pan­sion of a virus pro­duc­tion sys­tem in Tan­zania to cre­ate a nat­ural pesti­cide called SpexNPV to fight the worm. Sci­ent­ists have tested the virus, as well as loc­ally-grown neem, and shown that both kill the worm.

Over half of farm­ers in Tan­zania have neem trees, and can use both leaves and ber­ries to fight the worm. But it takes a lot of leaves to gen­er­ate a pesti­cide set­ting up prob­lems of bulk. However, the virus is much less bulky, and is being made so that it is held in a light clay solu­tion that is then dried ready for re­hyd­rat­ing and spray­ing.

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The tech­no­logy to pro­duce the virus loc­ally has been brought in from Brazil and will ini­tially cre­ate enough virus to treat around 10,000 ha a year, and later to meet the re­gional need of 100,000 ha a year. The pro­ject is being fun­ded through the Re­search into Use Pro­gramme (RUI) fun­ded by the UK De­part­ment for In­ter­na­tional De­vel­op­ment (DFID)

The double break­through of an early warn­ing sys­tem and nat­ural pesti­cides come at a time when the gov­ern­ment is spend­ing over Sh70m a year on pesti­cide to head off the mi­grat­ory pest. Moreover, with much of Sub Saha­ran Africa in­clud­ing Kenya hav­ing ex­per­i­enced bet­ter rain­fall this year, sci­ent­ists are warn­ing this can provide con­du­cive breed­ing con­di­tions for the pests. Already, over 120,000 farm fam­il­ies in Malawi re­por­ted the de­struc­tion of 35,000 hec­tares of crop in Janu­ary last year.

The worst at­tack was in Liberia in 2009, where army­worms at­tacked about 100 vil­lages and dam­aged crops, in­clud­ing cof­fee plant­a­tions and pas­ture. Over 500,000 people were af­fected, and over 20,000 res­id­ents were forced to flee their homes.