Seasonal activity and environmental and hormonal regulation of development and diapause were studied in three different orders of tropical insects at Barro Colorado Island (9°N), Panama.

The seed bug, Jadera aeola, reproduces in the late dry season coincident with mass production of its food, seeds of Sapindaceae. Newly emerged adults enter diapause. Population density and food, but not photoperiod, appear to be involved in diapause regulation. Juvenile hormone analogue (JHA) stimulates sexual maturation in both sexes.

The fungus beetle, Stenotarsus rotundus, aggregates at the base of a palm tree where it remains in imaginal diapause for up to 10 months. In addition to daylength (Tanaka et al., 1987), humidity plays an important role in regulating diapause termination. Gonad and flight muscle development occur more rapidly at high humidity than at low humidity. Beetles treated with JHA initiate oocyte and flight muscle development but not testis development. 20-hydroxyecdysone has no effect on diapause termination.

Flesh flies (Sarcophagidae), when monitored with a meat-baited trap, show striking seasonal fluctuations in abundance. Yet, we found no evidence for diapause in three fly species reared in the laboratory under a range of photoperiod and temperature conditions.

The suitability of Chilo partellus (Swinh.) larvae reared on gram (Cicer arietinum) flour diet, for rearing of the parasite, Apanteles flavipes (Cam.), was determined. The successful parasitism on diet fed or control larvae (reared on maize stems) was almost equal. There was also no significant difference in the mean egg-larval period of the parasite developed on both kinds of the hosts. However, on diet reared larvae, significantly more parasite grubs (20.3/host) failed to pupate as compared with control larvae (3.5/host). Consequently, the parasite cocoon production/host on them declined significantly but not drastically as they supported more number of parasite grubs/host as compared to control larvae.

Reasons of the failure of parasite grubs to pupate in diet are not certain but considering all the biological attributes of the parasite developed on diet reared larvae, the diet is recommended for its mass multiplication.

The sensitivity of 1-day-old eggs of Corcyra cephalonica Staint., to ionizing radiation has been investigated in view of a possible future application of sterile-insect technique to the control of this species. Further, the irradiation effects on subsequent developmental stages were evaluated. A dose of 5 krad prevented hatching of eggs, while a dose of 4 krad was the highest dose that allowed an adequate percentage of the irradiated eggs (28.23) to complete development to the adult stage. While the mating percentage and mating frequency of resultant adults appeared to be unaffected, the percentage of multiple mating was variable and no clear pattern emerged. Egg production and fertility of P1 adults was decreased significantly and all effects of the treatment were more severe for pairings of both sexes resulting from irradiated eggs than pairings of either sex with unirradiated partners. However, the results show that a dose of irradiation low enough to permit adequate numbers of adults to develop from irradiated eggs (4 krad) is insufficient to induce high levels of sterility. Therefore, irradiation of eggs for mass production of either sterile or partially sterile adults was found not to be feasible.

The mandarin orange or portugal, Citrus reticulata (Blanco), is unattractive as a forage material for the leaf-cutting ant, Acromyrmex octospinosus (Reich) while pineapple orange, Citrus sinensis (L.), is quite attractive. Lipid and non-lipid components were separated from portugal whole leaf extracts. Bioassays revealed the lipid fraction to be less attractive to the ants. This fraction was further separated using preparative layer chromatography into polar and non-polar lipid constituents. Two non-polar lipid fractions, Rf 0.5–0.7 and Rf 0.7–1.0, were shown to be the most deterrent constituents of portugal leaves to A. octospinosus.

Because seasonality in tropical habitats is controlled primarily by variations in rainfall rather than variations in temperature, it is frequently less predictable in timing, and spatially more patchy than seasonality in temperate habitats. This constrains the ways in which tropical species can adapt to seasonally adverse conditions, and in particular, may give greater importance to migratory behaviour as a component of seasonal adaptation.

Australian pierid and nymphalid butterflies illustrate these points. The species studied are present as adults during the dry season. Some undergo a reproductive diapause while others breed continuously. Major seasonal shifts in geographic distribution are a conspicuous feature of their biology, except in species whose reproduction is cued directly by rainfall, or are restricted to less seasonal microhabitats. Reproductive diapause is often associated with aggregation and with non-melanic polyphenism. Reasons for spending the dry season as an adult may include the fact that adult food remains available through the dry season even though larval resources disappear, and an improved capacity for opportunistic dispersal before breeding begins. The use of direct rainfall cues to control diapause may exclude non-migratory species from subtropical or temperate regions.

A laboratory study was carried out in Egypt to determine the effect of combining treatments of gamma radiation and methyl bromide fumigation applied to adults of Tribolium confusum (Duv.). An interaction between irradiation and insecticidal treatment was obvious, with additive effects noted at most combination treatments. When the irradiation treatments were applied first and fumigation were accomplished within 24 hr., the intermediate dosage of irradiation (6 krad) afforded the insects some protection against marginally effective dosages of methyl bromide after 14 days. On the contrary, it is evident that a possible synergistic effect of irradiation pretreatment followed by chemical exposure, after 21 days, where all of irradiation dosages used (2-10 krad) enhanced the fumigant effectiveness. On the other hand, when the irradiation dosages were increased from 5-50 krad and followed by fumigant treatments after 7 days, the trend did continue where all combination treatments killed more insects than did either treatment applied alone. Conversely, when fumigation preceded treatment with irradiation the sublethal methyl bromide fumigation also apparently leaves the surviving insects in a debilitated state and became more radiosensitive.

In general, the effects from combination of irradiation and fumigation were more effective than were the effects of either treatment given singly, whether irradiation preceded insecticidal treatment or vice versa.

Neomachilellus scandens (Machiloidea; Wygodzinsky, 1978) is a litter inhabitant of inundation forests in the Rio Negro valley, which are annually flooded for 5–6 months. At the beginning of the non-inundation period, juveniles hatch from previously submerged eggs on the forest floor and reach maturity after 3–4 months. Adults propagate in the litter where females deposit their eggs which are subjected to the next flooding. Both sexes subsequently migrate into the trunk/canopy area and perish. In nearby primary and secondary dryland forests N. scandens has no defined reproduction period and juvenile stages are found throughout the year.

Cutworms, semiloopers, budworms and armyworms in the genera Agrotis, Chrysodeixis, Heliothis, Mythimna, Persectania and Spodoptera are important pasture and crop pests in Australia. They comprise both cosmopolitan species, such as A. ipsilon, H. armigera, M. separata and S. exempta and endemic species such as A. infusa, H. punctigera, M. convecta, P. ewingii and P. dyscrita. Although the cosmopolitan species are major pests of parts of Asia and Africa, they are, with the exception of H. armigera, less important agricultural pests in Australia than their endemic counterparts. The latter are widely distributed outside cropping areas, because they breed on a wide range of native host plants as well as on introduced crops and pastures and also have the potential to invade cropping areas from native habitats. The cosmopolitan species are largely confined to tropical and subtropical summer crops and improved pastures of north and east Australia where chronic infestations often develop although major outbreaks and migration out of cropping areas are rare. Periodic outbreaks of endemic species result from an unusually favourable growth of vegetation in early autumn, following drought-breaking rains in the inland. Moths arrive in the rain-affected areas as a result of migration and concentration by rain-bearing troughs and depressions. Southward migration of their progeny occurs in spring on warm northerly airflows produced ahead of eastward-moving cold fronts and results in invasions of temperate crops and pastures. Migration also occurs in anticyclonic conditions, resulting in an extensive redistribution of populations and is adapted to the erratic distribution of rainfall in inland Australia. Among cosmopolitan species, only Spodoptera spp. cause outbreaks which are infrequent and occur with the onset of summer rains in coastal and sub-coastal areas. Most movements of cosmopolitan species are confined within cropping areas although migration from coastal to inland crops, under the influence of prevailing SE winds, and in frontal systems, troughs and storm outflows, is also suspected.

The larvicidal activity of two entomopathogenic bacteria Bacillus thuringiensis H-14 and B. sphaericus 1593 against mosquito larvae of Culex pipiens has been evaluated. According to LC50 values obtained, B. thuringiensis (4.6 x 105 spores/ml) proved to be highly pathogenic to fourth instar larvae than fi. sphaericus (4.2 x 106 spores/ml).

Larval treatment with LC50 levels of both pathogens affected the reproductive potential of surviving adults during two successive gonotrophic cycles. These treatments caused insignificant changes in some basic morphometric characteristics of mosquito females that developed from surviving larvae.

The fall armyworm, Spodoptera frugiperda (J. E. Smith), has a high reproductive rate of 900–1000 eggs per female, a relatively short generation time of 30 days and good dispersal ability. These traits make it a successful colonizing species. There is a large body of circumstantial evidence that migration is a major component in the life history strategy of this species. Although the fall armyworm is unable to survive the winter in the United States except in southern areas of Florida and Texas, it redistributes itself over most of the eastern United States each growing season. Long-range movement from Mississippi to Canada in 30 hr on a low-level jet stream was documented on one occasion with synoptic weather maps. Many fall armyworm moths have been collected in the Gulf of Mexico as far as 250 km from land, indicating the possibility of seasonal trans-Gulf migration between the United States and the tropics. Electrophoretic analyses of populations of a corn “race” of fall armyworm collected throughout the Caribbean Basin indicated low genetic heterogeneity. Nei's genetic distance estimate (0.015) and Wright's Fst value (0.032) both suggested undifferentiated populations with interbreeding across the entire geographic range. Wet and dry seasons in the east and west coast of Central America and elsewhere in the tropics alternate with each other so that only one habitat is available at a time. This fluctuation in available habitat is proposed as the templet that led to the evolution and maintenance of migration in the colonizing life history strategy of the fall armyworm.

In tomato, infestation by the natural population of the fruit borer, Heliothis armigera (Hubner), on number basis was positively correlated with infestation on weight basis. Infestation was negatively correlated with the number of flowers per inflorescence. Surface texture of calyx also affected the susceptibility of the genotype. Reducing sugars in fruits were positively correlated, while zinc and iron content in foliage and ascorbic acid contents in fruits were negatively correlated with degree of infestation. Coefficient of determination revealed that 87% variability in borer infestation was due to zinc, iron, ascorbic acid and reducing sugar content.