Cabbage Integrated Pest Management : An Ecological Guide.

Major Cabbage Insect PestsRelated exercises from CABI Bioscience/FAO manual4-D.1 Predation on sucking insects in insect zoo4-D.2 Cage exclusion of natural enemies in the field4-D.7 Parasitism of whitefly5.11 Stemborer – Melanagromyza cleomaeDuring IPM training exercises in Lao PDR (1997) and northern and central Thailand (1999, 2000), thestemborer Melanagromyza cleomae was found in stems of cabbage seedlings and petioles of olderplants. Very little is known about this stemborer fly.M. cleomae appears to attack only crops in the crucifer family. It must be considered a potential pest onimportant crops on a wider scale than so far reported in literature (CABI ID report, 2000). Much of thedocumented information on M. cleomae in below section is based on innovative action-research byfarmers, IPM trainers and field-based researchers, during above mentioned IPM training exercises (pers.comm. J. W. Ketelaar, 1999/2000).Description and life cycleThe adult is a fly, approximately 2 mm long, mostly black with red eyes and a slight blue-green cast onthe back of the thorax and abdomen. Eggs are inserted into plant tissue. Larvae are small white maggotswith no legs. Pupation occurs inside the tunnels formed by the larvae in plant tissue.In northern Thailand, IPM trainers reared aromyzid stem borers and their parasitoids from weeds (compositefamily) surrounding the cabbage fields. These stemborers were identified as Melanagromyza metallica.This means that the cabbage stemborer is probably not using the prevalent composite weeds as alternativehosts. Further ecological studies are needed to study alternative hosts (pers.comm. Dr. M. Schmaedick,2000)Plant damage and plant compensationThe larvae (maggots) of this stemborer fly, bore into the main stems of cabbage plants, often youngcabbage transplants. The main symptom is plant stunting. The transplants usually survive but show veryweak growth, discoloration of leaves and do not form heads. In older plants the larvae are ofund boring inthe petioles of older leaves. It is not certain what effect, if any, this damage to the older petioles may haveon cabbage yield. Fields infested at this stage may, however, produce large numbers of flies that couldinfest nearby fields.Damage symptoms caused by the stemborer is often confused by farmerswith stunting due to lack of water or fertilizers.Serious crop damage occurred in young cabbage transplants during atraining activity in Chiangrai province, northern Thailand. Interestingly, itseemed that there was a difference in stemborer occurrence in the plotthat was fertilized according to Farmer Practice (high level of infestation)as compared to the IPM plot which received fertilizer according torecommended rate after soil analysis (low infestation). The main differencein fertilizer treatment was that the IPM plot received a high input of organicfertilizer, and the FP plot received only chemical fertilizers.larva in the stem or root107 Cabbage Ecological Guide - 2000