The incidence of the American serpentine leafminer, Liriomyza trifolii (Burgess) (Diptera: Agromyzidae) was studied in cotton-growing tracts of Tamil Nadu State, India. The incidence was higher on summer than on winter cotton and the cropping pattern was found to have an impact on the incidence of the leafminer on cotton. Biological studies on L. trifolii conducted on cotton, Gossypium hirsutum L., tomato, Lycopersicon esculentum Mill., and cowpea, Vigna sinensis (L.) Walp., revealed that its life cycle varied with different hosts. The duration of the pupal stage of L. trifolii was the longest in the leafminer's life cycle. Lycopersicon esculentum was the preferred host—females of L. trifolii survived the longest and had the highest fecundity on this host. Sex discrimination was possible at the pupal stage, on the basis of size; female adults were found to emerge from larger-sized pupae and males from smaller ones.

Experiments were carried out to determine the factors that influence the feeding behaviour of Culex tigripes, a mosquito whose larvae are predators of other mosquito larvae. The results indicated that the efficiency of predatory activities of Cx tigripes larvae increased as they developed from 1st to 4th instar with regard to the number of mosquito prey larvae they consumed in a given period of time. Fourth instars of Cx tigripes are the most voracious of all the stages and are better adapted for catching and consuming all stages of mosquito larvae. The mean number of mosquito larvae consumed in 24 hours increased with increasing prey density. When offered a mixture of different prey species and larval stages, Cx tigripes larvae consistently selected 4th instars of mosquitoes over pupae and preferred Aedes aegypti larvae to the larvae of Cx quinquefasciatus and Anopheles gambiae. Prey size, density and mobility were also found to influence prey selection by Cx tigripes.

The development and morphometrics of the whitefly Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) were studied on cassava and a description was made of the different nymphal instars and oter biological characteristics. The nymphal instars were distinguished using easily recognisable morphological characteristics. Abnormally developing individuals were also easily recognised. Regression analysis was highly significant between the length and width of nymphal instars modelled collectively indicating two-dimensional growth at least across three nymphal stadia. Males were smaller than females on the basis of body length, wing width and width of the abdomen. The insects showed better development on a Colombian cassava variety as compared to an African variety, Ebwanateraka from Uganda, and consistently showed a higher proportion of males than females (2.33: 1) for early-emerging individuals. Mean developmental period on both varieties was 22 days and the first instars accounted for the major part of the developmental period which ranged from 19 to 29 days. The mean number of eggs/female/day was 4.89. The actual events of first instar eclosion, which can last up to approximately five minutes, were described. The intervals of honeydew flow to the vasiform orifice lasted a minimum mean time of 20.8 seconds and a maximum mean time of 123 seconds.

Growth, development and fecundity of Maruca vitrata Fabricius (Lepidoptera: Crambidae) were studied on artificial diet and flowers of two accessions each of three wild Vigna species, namely V. vexillata (TVnu 594 and TVnu 72), V. oblongifolia (TVnu 957 and TVnu 42) and V. unguiculata ssp. dekindtiana (TVnu 979 and TVnu 863) and six accessions of cowpea, V. unguiculata ssp. unguiculata (Moussa Local, VICAM-1, TVu 13731, IT84S-2246, IT89KD-457 and IT91K-180). The percentage survival of the larvae, larval weights as well as growth and development indices were significantly higher on the artificial diet, flowers of cowpea cultivars and those of V. unguiculata ssp. dekindtiana compared to those of V. vexillata and V. oblongifolia. The fecundity of females from larvae reared on artificial diet and flowers of cowpea was also significantly higher than that of females from the wild Vigna genotypes. All variables were included in principal component analysis. Two components accounted for 81.79%. On the basis of this analysis, the diets appeared to fall into four categories based on their suitability for supporting development of M. vitrata: unsuitable (TVnu 42 and TVnu 957), fairly suitable (TVnu 72, TVnu 594, TVnu 979, Moussa Local and TVnu 863), suitable (IT89KD-457, IT91K-180, VICAM-1, TVu 13731 and IT84S-2246), and very suitable (artificial diet). The importance of these findings in the development of host plant resistance of cowpea to M. vitrata is discussed.

The development, life table and intrinsic rate of natural increase of the reduviid predator Rhynocoris fuscipes (Fabricius) on Spodoptera litura Fab., Earias vittella Fab. and Corcyra cephalonica Stainton under laboratory conditions were constructed. Fecundity, longevity and minimum developmental period of the predator were dependent on the prey diet and decreased in the order: S. litura, E. vittella and C. cephalonica. The mean number of female progeny produced over the entire period (the gross reproductive rate) was 43.0, 37.5 and 32.5 on S. litura, E. vittella and C. cephalonica respectively. The net reproductive rate (Ro), intrinsic rate of increase (rc) and weekly multiplication rate were also highest on S. litura followed by E. vittella and C. cephalonica.

The developmental potential of the palm aphid Cerataphis palmae Ghesquière (Homoptera: Pemphigidae) on three dwarf coconut varieties—Malayan dwarf red (Mdr), Malayan dwarf green (Mdg) and Malayan dwarf yellow (Mdy)—was studied in a screenhouse using leaf clip-on cages. Under similar temperature (30°C ± 1.13) and relative humidity (69.8% ± 1.63) conditions, the aphid expressed significant differences in fecundity, longevity and developmental period on the coconut varieties. The total developmental period on Mdr lasted 12.17 ± 0.76 days while on Mdg and Mdy it was 14.84 ± 0.63 and 13.83 ± 1.05 days, respectively. Thus the aphid population increased on the dwarf red variety over a significantly shorter period than it did on the other two varieties. Furthermore, fecundity and longevity of C. palmae on Mdr were significantly higher than on the Mdg and Mdy varieties (P < 0.01). These results indicate that Mdr supports C. palmae development better than the other two palm varieties.

Wild Glossina austeni and G. pallidipes appear in many different populations. All conspecific flies possess similar surface hydrocarbons that include species-specific contact sex pheromones. Recently, evidence for a contact sex stimulant was found in the surface hydrocarbons extracted from female G. austeni. The bioactive hydrocarbon fraction contained alkanes and unsaturated hydrocarbons that were separated and analysed by GC/GC-MS. The structure and relative abundances of alkanes and alkenes from several populations of laboratory and wild collected specimens appeared to be similar.

Similarly, the alkanes of conspecific female G. pallidipes from several locations were analysed to determine differences and similarities with older, published work on the sex pheromone of the species. The components were analysed by GC-MS and were very similar across populations. If major components were compared, only minor variation was observed between females from Zimbabwe (wild), Amsterdam, ICIPE/Kenya, Kenya, Tanzania (wild), Uganda/Bristol and Arba Minch/Ethiopia. The absolute meaning of these differences is not known, since the activity of synthetic sex pheromones was shown conclusively against Wageningen and ICIPE males in 1984–1986 tests, although they were less active against Zimbabwe males.

Methanolic extracts of stems and roots of silver fern, Cheilanthes farinosa Kaulf., (Polypodiaceae: Pteridophyta) incorporated into a semi-synthetic diet significantly extended the larval period, reduced pupal weight and adversely affected pupation of the cotton bollworm, Helicoverpa armigera (Hübner) (Noctuidae: Lepidoptera). Early third instars were more susceptible to the treatment than late third instars. A steroidal fraction (Rf 0.7) from the methanolic extract significantly reduced mean larval weight but did not affect pupation. A major ecdysteroidal component (R.t. 9.233 min.) was purified by reverse phase HPLC of this fraction, along with two minor components. The total yield of ecdysteroids was 564 mg/kg of shade-dried root and stem matter. Pooled HPLC fractions, when injected into final instars, resulted in dose-dependent effects on larval-pupal transformation. Adults emerging from treated larvae failed to lay eggs and were shorter-lived than their untreated counterparts.

Lufenuron, N–[2, 5–dichloro–4–(1, 1, 2, 3, 3, 3– hexafluoropropoxy) –phenylaminocarbonyl]–2, 6–difluorobenzamide, a novel acylurea insect growth regulator, exerted significant sublethal effects in larvae, pupae and adults of the diamondback moth, Plutella xylostella (Linnaeus) (Lepidoptera: Plutellidae). Second, third and fourth instars were treated at their respective LCM using a standard 'leaf–disc dip' method of bioassay. Sizes and weights of pupae from the treated lots were significantly reduced but larval and pupal durations remained unaffected. All the pupae formed from larvae treated as fourth instars were deformed and produced no adults. Only 38 and 14% of adults emerged from the pupae formed following treatment at the second and third instar, respectively, as compared to 88–92% adult emergence in the controls. Apart from significant reduction in body length, some adults from the treatments had fringed and twisted wings which prevented normal flight. IGR treatment also resulted in pronounced reduction in fecundity (up to 10.2 eggs per female in comparison with 135.8 per female in the control) and oviposition periods (up to 3.2 days in comparison to 7.8 days in the control). Field trials to investigate the management of P. xylostella using lufenuron are recommended.