Beauveria bassiana is characterized by having a white hyphae and white spores. The conidia are globose to broadly ellipsoid. There is usually a dense white growth of hyphae on the outer surface of the host. The oval, white spores can be seen clumped together into spore balls under high magnification.

B. bassiana is a common soil-borne saprophytic fungus that occurs worldwide.  It has a number of strains with different pathogenicity, virulence and host range.

Sweetpotato weevil and other species of beetles, moths, bugs and grasshoppers. It is commonly found infecting insects inhabiting the soil.

The early infective stage of N. rileyi is a white mass of fungus covering the larva. After a few days, the spores are formed and the larva becomes pale green due to heavy accumulation of green spores.

Nomuraea rileyi attacks the larvae of stems borers, leaffolders, and armyworms.

Nuclear Polyhedrosis Virus (NPV).

Description

In the late stages of infection, larvae infected with NPV turn white and become swollen and sluggish. Just before the larva dies, it climbs the tops of the plant and attaches itself to the leaves. After death, the larva quickly turns brown and black, the internal contents become liquefied and the integument becomes fragile. The integument ruptures releasing liquid containing polyhedral bodies of the virus. Larvae die within 3-4 days after ingesting the virus.

Hosts

Larvae of Spodoptera litura, S. exigua (army worms) and other lepidopterous larvae.

Bacillus thuriengiensis Berliner.

Description

At early stage of infection the larvae stop feeding. Subsequent symptoms include vomiting, diarrhoea, general sluggishness, and general paralysis. Death may follow immediately or in an hour to a few days. Sublethal effects may include reduced feeding, shorter larval and adult life span, lower fecundity, reduced larval and adult body weight.

Hosts

Larvae of the insect orders Lepidoptera (moths and butterflies), Diptera (flies), and Coleoptera (beetles and weevils).

Heterorhabditis and Steinernematis spp.

Description

These microscopic worm-like, soil-borne animals are able to locate and infect weevil larvae within storage roots.  The nematodes infect the gut of the insect, and cause death within about three days.  Pupae and adults may also be infected but are less susceptible.  Trials have demonstrated considerable reductions in weevil populations and damage after applying nematodes to weevil-infested sweetpotato crops.  However, naturally occurring nematode populations are unlikely to provide significant control, and the cost of producing the inoculum remains a barrier to widespread use.

Hosts

Larvae of the insect order Coleoptera (beetles and weevils).

References

Amalin, D.M. and E.A. Vasquez. 1993. A Handbook on Philippine Sweet Potato Arthropod Pests and their Natural Enemies. International Potato Center, Los Baños, Laguna, Philippines. 82 pp.

Bajwa, W. I. 2001. Insect-pathogenic bacteria. http://www.ippc.orst.edu/biocontrol/biopesticides/papers/bacteria-ent-pathogens.html Integrated Plant Protection Center (IPPC) Oregon State University, Corvallis. 26 September, 2002.

Mahr, S. The Entomopathogen Beauveria bassiana. http://www.entomology.wisc.edu/mbcn/kyf410.html. University of Wisconsin- Madison. 08 August 2003.

Shepard, B.M., G.R. Carner, A.T. Barrion, P.A.C. Ooi and H. van den Berg. 1999. Insects and their Natural Enemies Associated with Vegetables and Soybean in Southeast Asia. Quality Pronting Co. SC. USA. 108 pp.

Contributed by: Erlinda Vasquez and Vilma Amante