The reasons for assessing crop losses due to pests of cereals are reviewed; for making decisions in pest management based on costs and benefits, for allocating resources on the most important pests, and as a guide to how yield is lost. Crop yield is seen as a balanced system, with inputs and output. The methods of quantifying pest attack, measuring losses and the difficulties met are discussed: the interaction of losses, interplot interference, mixed crops, loss distribution and crop compensation. Surveys of loss are described, with examples.

Three 9-acridone alkaloids, melicopicine, tecleanthine and 6-methoxy tecleanthine were isolated from the bark of Teclea trichocarpa. Melicopicine and tecleanthine exhibited mild antifeedant activity against the African armyworm, Spodoptera exempta. All the three alkaloids showed antimicrobial activity against the fungus, Cladosporium cucumerinum and the bacterium, Bacillus subtilis.

After field screening local germplasm for stem-borer (Chilo partellus, Swin.) resistance for four seasons in two years we identified two sources of resistance, Katumani and Kitale. A cross between them performed better than either of the parents. When exotic lines from CIMMYT, Mexico, reported to be resistant to South and Central American stem-borers were screened at Mbita Point Field Station, to test and confirm their resistance to East African stem-borers, a number of them were found to be resistant to Chilo. It was also noted that the level of their resistance was higher and more broadly based than the local source. This shows that the source of origin is always full of genetic variability. This finding now suggests that a cross between the local and exotic sources should offer a wide scope in the multiple resistance or the multiline approach towards pest management.

Parasitization of P. brassicae L. by A. glomeratus L. was found to be between 63.79 and 76.52% in Farm 1 and 92.68 and 93.43% in Farm 2. Population density of the parasitoids ranged between 35.16 ± 6.05 and 57.76 ± 13.20. The developmental period of the parasitoids within the host was 21 days and the pupal period 9 to 10 days. The population of the parasitoid showed a steady increase during November–December. The rate of pupation of P. brassicae showed a decline from 36.21% in mid-November to 23.48% in later November in Farm 1 with an early crop. In Farm 2 with a late crop the pupation rate dwindled from an already low 7.32 to 6.57% by late December.

The results of five experiments on maize resistance to Chilo partellus, suggest that there are at least five levels of relationships affecting plant colonization, larval survival and damage level: non-acceptance for oviposition shown by Inbred D and G and CIMMYT lines 125, 33, 324 and 178 (s3). Preferred Inbred A was oviposited 2–3 times higher. Feeding of young larval instars on young leaves or leaf sheaths, reduced on CIMMYT lines 324, 125 and 33; concentration of feeding of young larval instars on the upper growing part of plant, extensive on the highly susceptible Inbred A and reduced on all resistant lines tested; penetration of young larval instars into stem, reduced on CIMMYT lines 34 and 125 and Inbred G; and feeding of older larval instars in stem, reduced on CIMMYT lines 324, 178, 125 and Inbred G.

Field observations on Chilo infestation of 100 promising sorghum lines showed that there are six levels of relationship affecting plant colonization and damage level by stem-borers: non-preference for oviposition (E 302, E 303, IS 1044, IS 1151, IS 2162, IS 4660, IS 17739, IS 18328, IS 18349, IS 18479, and IS 18489); feeding of the first larval instars on young leaves (reduced on E 302, E 303, IS 1044, IS 2162, IS 2209, IS 18349 and IS 18427); causing of ‘dead hearts’ by young larval instars due to extensive feeding in stems of young plants (lower for IS 2162, IS 2263, IS 18328, IS 18349); tunnelling (extent and location) of older instars in stems (low in IS 4660, IS 18427 and IS 18479); tolerance of plants to leaf damage (in spite of high damage, plants form panicles) (IS 2205); and tolerance of plants to larval feeding in stems (in spite of high tunnelling, the plants form seeds). The effect of a number of cultivars showing different levels and mechanisms of resistance on the Chilo behaviour and biology was studied in depth under field conditions.

Studies on the relative abundance of pod-borers and distribution patterns of the dominant borer, Adisura atkinsoni Moore, were conducted at Bangalore (Karnataka, India) with a view to develop a field screening procedure in the field bean, Lablab niger, to pod-borers. Nine species of borers constituted the borer complex on L. niger. The borers population peaked in October.

Eggs and early instar larvae of Adisura followed a clumped distribution pattern. Older larvae, however, were distributed uniformly in the field. Adisura moths preferred to lay eggs between 50.8 and 63.5 cm on the erect type of L. niger and between 101.6 and 114.3 cm on the creeping type of the plant. Plant height had a significant positive correlation with the maximum number of Adisura eggs, but up to nearly 115 cm. Adisura eggs peaked in number during October, while larvae did so during November–December. Implications of the aforementioned observations in field screening are suggested.

Seventy cultivare of sorghum representing recently released varieties, hybrids, experimental varieties, lines bred for stalk-borer resistance and local resistant stocks were tested for stalk-borer resistance under artificial infestation during monsoon (July–October) season. There were significant differences among varieties for leaf-feeding injury, per cent ‘dead hearts’, number of holes and tunnels and per cent tunnelling. Released hybrids and local varieties were susceptible for different parameters. Thirteen varieties viz., SPV Nos. 35, 103, 107, 110, 135, 140, 192, 229, E 302, E 304, P 37, R 133 and CSV-8R were at par with resistant varieties for per cent tunnelling per plant. Long peduncle varieties were relatively susceptible.

Leaf-feeding injury, per cent ‘dead hearts’ and tunnelling parameters were not significantly correlated and independent of each and none of them could be related to grain yield. Number of holes, number of tunnels and per cent tunnelling were positively correlated. Thus, number of holes per plant or internode may be a good indicator of per cent tunnelling and can conveniently be used as a criterion for evaluating germplasm to stalk-borer (Chilo partellus Swin.) resistance. The varieties CSV-8R, SPV-35, SPV-103, SPV-140 and SPV-192 were identified as promising sources of resistance to stalk-borer.

Genetic analysis of sorghum resistance to stem-borers was performed in a 6 × 6 diallel cross. The results indicated that resistance to stem-borers is polygenically inherited. F1 hybrids did not differ significantly from mid-parental values suggesting intermediate inheritance. However, resistance was partially dominant to susceptibility. Combining ability analysis showed that resistance to primary damage, i.e. % ‘dead heart’ was governed by both additive and non-additive type of gene actions while secondary damage, i.e. % stem tunnelling was governed predominantly by additive gene action. It was noted that the inheritance patterns of primary and secondary damage were different. Tunnel length showed positive correlation with the number of larvae per plant and negative association with plant height, but had no correlation with grain yield per plant. On the basis of larvae recovered from the tunnelled plants, Chilo partellus was found to be the predominant stem-borer species followed by Sesamia calamistis, Eldana saccharina and Busseola fusca. Significance of genetic studies of host plant resistance in deciding breeding strategies for insect resistance has been discussed.

The insect growth regulator, 6′,7′-epoxy-3′-ethyl-7′-methyl-dec-2′-enyl 6-ethyl-3-pyridyl ether, at 10 ppm applied to rearing media, did not prevent oviposition or hatchability of the eggs of Tribolium confusum. The insect growth regulator (IGR) apparently had no effects on the development of younger larvae, and no morphological abnormalities were observed in these instars. However, the IGR prevented metamorphosis of the last larval instar. These larvae continued to moult several times, became larger than larvae in untreated food, but failed to pupate; as a result, no adults emerged from the treatments.

Ten rice varieties were studied for their relative susceptibility to the stalk-eyed fly, Diopsis thoracica West. Preference for oviposition was observed and some of the factors which appeared to pre-dispose the plants for oviposition were number of tillers per hill, leaf angle, plant height, stem diameter, leaf colour, plant age and plant spacing. The relative developments of Diopsis thoracica in the different varieties are given. Varietal susceptibility to infestation by the insect seemed to be different from varietal suitability for its growth. Insect damage affected the yield components and total yields, but the extent was varietal. The level of infestation, the production and time of production of compensatory tillers seem to be important factors in yield reductions. Implications of some of these results in a pest management programme are highlighted.

The development of a mass-rearing technique of Mantea testulalis by the ICIPE has allowed us to start extensive work on cowpea resistance to the legume pod-borer. A preliminary field observation showed that the cowpea resistance is on the low level. Therefore, our effort initially concentrated on the development of new methods and techniques which were sufficiently sensitive to separate lines possessing small differences of resistance. Eight different treatments were used to develop the methodology of cowpea screening under artificial infestation with Maruca larvae and eggs in the screenhouses and seven treatments in the field.

Plant growing stage has modified the expression of cowpea resistance to Maruca larvae. Five-seven shoots stage (not younger) was found to be most suitable for screening for resistance in pre-flowering period. By using five eggs/plant in pre-flowering stage on cowpea plants grown on the ground, it was possible to differentiate between the resistant and susceptible lines. The standard error between plants treated with 10 eggs/plant treatment was lower than those with five eggs/plant treatment. Therefore, if laboratory colony allows the higher infestation of 10 eggs/plant, it is recommended. Using 10 or 20 eggs/plant in flowering stage correctly segregated cowpea lines for resistance and susceptibility based on larval survival and damage level of flower buds, flowers and pods.

Three cowpea cultivars, TVu 946, Ife Brown and Vita 1 were examined for resistance to the legume pod-borer, Maruca testulalis (Geyer). TVu 946 was found to be the most resistant in both the flowering and pre-flowering stages, followed by Ife Brown and Vita 1, respectively. Field and screen-house experiments show that Maruca larvae caused significantly less damage on TVu 946 than on Ife Brown and Vita 1. In addition, larval survival and development on TVu 946 was the most negatively affected. Screenhouse experiments in a choice situation clearly show non-preference of TVu 946 for oviposition by adult Maruca females, and biochemical studies show evidence of antibiosis due to nutritional and antibiotic factor(s).

Eleetrophysiological recordings from taste sensilla of larvae of Chilo partellus (Swinhoe), Eldana saccharina Wlk. and Maruca testulalis (Geyer) during stimulation with various plant substances revealed that in the medial and lateral maxillary sensilla styloconica of each of these three species a NaCl, water and sucrose sensitive cell is present. In the medial styloconic sensilla of C. partellus, an additional chlorogenic acid sensitive cell occurs. Chilo partellus and E. saccharina appeared to be more sensitive to sucrose than M. testulalis. In all three species, the lateral sensilla styloconica are more responsive to sucrose and less responsive to NaCl than the medial ones.