Field Crops

Suitability of Corn Insects for Green Lacewings

A variety of factors need to be considered in evaluating the potential importance of predators in biological control of insect pests, including feeding preferences, consumption rates, and survival and development on different prey species. Obrycki et al. (1989) evaluated the effect on development rates and survival of two green lacewing species feeding on different insect pests they potentially would encounter in corn.

Immature development of the common green lacewing, Chrysoperla carnea, required 20.5, 21.6 and 24.9 days at 80F when fed upon European corn borer eggs, black cutworm eggs and newly hatched (neonate) black cutworm larvae, respectively. C. carnea immature mortality rates were 26% when reared on black cutworm eggs, 40% when reared on corn borer eggs, 65% on black cutworm neonates, and 100% when fed on European corn borer neonate larvae. Mortality of green lacewing immatures when fed European corn borer larvae was due to entanglement in the silk produced by the caterpillars. It is not clear if this would occur in the field where green lacewings encounter individual corn borer larvae, rather than the multiple larvae in a confined space like they encountered in the laboratory study. Each immature C. carnea consumed 377 European corn borer eggs, 641 black cutworm eggs, or 2,056 neonate black cutworm larvae during its development.

C. carnea and C. oculata first instar larvae were unable to survive on common stalk borer eggs. More than 80% of C. oculata larvae, reared on corn leaf aphids as first and second instars and then switched to feed on common stalk borer eggs as third instar larvae, died. Only 30% of C. carnea larvae treated similarly died. The most suitable prey, resulting in fastest development with highest survival was European corn borer and black cutworm eggs for C. carnea, and corn leaf aphids for C. oculata.

Source:

Obrycki, J. J., M. N. Hamid, A. S. Sajap, and L. C. Lewis. 1989. Suitability of corn insect pests for development and survival of Chrysoperla carnea and Chrysopa oculata. Environ. Entomol. 18: 1126-1130.

New Parasite of Lygus Bugs

The European braconid wasp Peristenus digoneutis is established and providing control of tarnished plant bug (Lygus lineolaris) in seven northeastern states. A related wasp, P. howardi, is a newly described species that was found parasitizing western tarnished plant bug (L. hesperus) nymphs in alfalfa grown for seed in Idaho. Parasitism rates were surprisingly high--up to 81% in first generation bugs one year. The average parasitism of about 50% is much higher than the average parasitism by native parasitoids in New Jersey (8%).

P. howardi is a native species that has three generations per year in the area in which it was studied. The 2.5 mm long black wasps are primarily females.

The geographic range of the wasp is uncertain. A few wasps were reared from bugs collected in Washington, as well as the ones from Idaho, so it is likely that the wasps occurs elsewhere in the region, from Oregon perhaps into southwestern Canada.

P. howardi readily parasitized L. lineolaris in laboratory tests, so it might be an effective biological control factor in the eastern United States, especially in more southern areas where P. digoneutis has failed to establish.

This wasp may be a practical biological control factor for alfalfa and other seed crops in the west, although further research is needed to understand its role in the control of various species of pest mirid bugs. Nothing is yet known about parasitism of lygus bugs by P. howardi on crops other than alfalfa. Also, despite high rates of parasitism in seed alfalfa, it remains to be determined if this suppression is sufficient to maintain western tarnished plant bug populations below the economic threshold.

Source:

Day, W. H., C. R. Baird, and S. R. Shaw . 1999. New, native species of Peristenus (Hymenoptera: Braconidae) parasitizing Lygus hesperus (Hemiptera: Miridae) in Idaho: Biology, importance, and description. Ann. Entomol. Soc. Amer. 92(3):370-375.


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