Relationship between oviposition preference and offspring performance in Australian Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae)

Abstract We investigated the oviposition preference and larval performance of Helicoverpa armigera under laboratory conditions to determine if the oviposition preference of individual females on maize, cowpea and cotton correlates with offspring performance on the leaves of the same host plants. The host-plant preference hierarchy of females did not correlate with their offspring performance. Female moths chose host plants that contributed less to their offspring fitness. Plant effects accounted for the largest amount of variation in offspring performance, while the effects of female (family) was low. The offspring of most females (80%, n  = 10) were broadly similar, but 20% (two out of 10), showed marked difference in their offspring performance across the host-plant species. Similarly, there was no relation between larval feeding preference and performance. However, like most laboratory experiments, our experi-mental design does not allow the evaluation of ecological factors (for example, natural enemies, host abundance, etc.) that can play an important role in larval performance in the field. Overall, the results highlight the importance of carrying out preference performance analysis on the individual or family level, rather than pooling individuals to obtain average population data.     

Effect of soil burial depth and wetting on mortality of diapausing larvae and patterns of post-diapause adult emergence of sorghum midge, Stenodiplosis sorghicola (Coquillett) (Diptera: Cecidomyiidae)

Abstract  In south-eastern Queensland, Australia, sorghum planted in early spring usually escapes sorghum midge, Stenodiplosis sorghicola , attack. Experiments were conducted to better understand the role of winter diapause in the population dynamics of this pest. Emergence patterns of adult midge from diapausing larvae on the soil surface and at various depths were investigated during spring to autumn of 1987/88–1989/90. From 1987/88 to 1989/90, 89%, 65% and 98% of adult emergence, respectively, occurred during November and December. Adult emergence from larvae diapausing on the soil surface was severely reduced due to high mortality attributed to surface soil temperatures in excess of 40°C, with much of this mortality occurring between mid-September and mid-October. Emergence of adults from the soil surface was considerably delayed in the 1988/89 season compared with larvae buried at 5 or 10 cm which had similar emergence patterns for all three seasons. In 1989/90, when a 1-cm-deep treatment was included, there was a 392% increase in adult emergence from this treatment compared with deeper treatments. Some diapausing larvae on the surface did not emerge at the end of summer in only 1 year (1989/90), when 28.0% of the larvae on the surface remained in diapause, whereas only 0.8% of the buried larvae remained in diapause. We conclude that the pattern of emergence explains why spring plantings of sorghum in south-eastern Queensland usually escape sorghum midge attack.     

Seasonal incidence of Stenodiplosis sorghicola (Coquillett) (Diptera: Cecidomyiidae) and its parasitoids on Sorghum halepense (L.) Pers. in south-eastern Queensland, Australia

Abstract  To quantify the role of Johnson grass, Sorghum halepense , in the population dynamics of the sorghum midge, Stenodiplosis sorghicola , patterns of flowering of Johnson grass and infestation by sorghum midge were studied in two different climatic environments in the Lockyer Valley and on the Darling Downs in south-eastern Queensland for 3 years. Parasitism levels of S. sorghicola were also recorded. In the Lockyer Valley, Johnson grass panicles were produced throughout the year but on the Darling Downs none were produced between June and September. In both areas, most panicle production occurred between November and March and infestation by S. sorghicola was the greatest during this period. The parasitism levels were between 20% and 50%. After emergence from winter diapause, one to two generations of S. sorghicola developed on S. halepense before commercial grain sorghum crops were available for infestation. Parasitoids recorded were: Aprostocetus diplosidis , Eupelmus australiensis and two species of Tetrastichus. Relationships between sorghum midge population growth rate and various environmental and population variables were investigated. Population size had a significant negative effect ( P  < 0.0001) on population growth rate. Mortality due to parasitism showed a significant positive density response ( P  < 0.0001). Temperature, rainfall, open pan evaporation, degree-days and host availability showed no significant effect on population growth rate. Given the phenology of sorghum production in south-eastern Queensland, Johnson grass provides an important bridging host, sustaining one to two generations of sorghum midge. Critical studies relating population change and build-up in sorghum to sorghum midge populations in Johnson grass are yet to be performed.     

Role of chemical cues from cotton in mediating host selection and oviposition behaviour in Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae)

We investigated the role of chemoreception in the host selection and oviposition behaviour of Helicoverpa armigera in the laboratory using five cotton genotypes and synthetic volatile terpenes. Female moths oviposited on substrates treated with methanol, ethanol, acetone and pentane extracts of leaves, squares and flowers of the cotton genotypes. Phytochemicals soluble in pentane were the most efficient in eliciting oviposition behaviour. In a two-way bioassay, pentane extracts of leaves or squares of a Multiple Host-plant Resistance genotype (MHR11), Deltapine commercial (DP90), and Smith Red Leaf (SRL) received significantly more eggs than solvent-treated controls. Extracts of squares of the native genotype Gossypium nelsonii did not receive more eggs. Females preferred DP90 and MHR11 to SRL and G. nelsonii. Female moths also laid more eggs on pentane extracts of MHR11 flowers than MHR11 leaves from preflowering, early flowering and peak-flowering plants. In a flight chamber, female moths used olfactory cues at short range to mediate oviposition and discrimination between host plants. Egg-laying, mated females were attracted at a distance (1.5 m) to volatile compounds released by whole plants and odours emanating from filter papers treated with synthetic volatile terpenes. Individually, the terpenes did not stimulate any significant oviposition response. However, there was a significant oviposition response to a mixture of equal volumes of the terpenes ( trans -β-caryophyllene, α-pinene, β-pinene, myrcene, β-bisabolol, and α-humulene). Conversely, antennectomised (moths with transected antennae), egg-laying, mated females did not stimulate any significant oviposition response. The significance of these findings in relation to H. armigera host-plant selection are discussed.     

Effects of physiological condition and experience on oviposition behaviour of Trichogramma australicum Girault (Hymenoptera: Trichogrammatidae) on eggs of Helicoverpa armigera Hübner (Lepidoptera: Noctuidae)

We produced an ethogram for and investigated effects of physiological condition and experience on oviposition behaviour for Trichogramma australicum on Helicoverpa armigera eggs. The data, coupled with the ethogram, have enabled the establishment of standard behavioural categories which can be used to assess acceptability of H. armigera eggs to T. australicum reared in vitro or in eggs of other species. Physiological and experiential conditions were investigated using females of three different ages (0–24, 24–48 and 48–72 h old), two types of sexual states (mated and unmated) and two types of ovipositional experience (naive and experienced). Durations of host finding, host examination, and post-ovipositional re-examination were reduced by oviposition experience and were shorter in younger females (0–48 h old). Oviposition experience reduces the duration of the drilling and percentage of females host-feeding. Being mated and young reduces the host examination time in subsequent oviposition bouts. Only ovipositionally inexperienced females host-feed before oviposition and host-fed more frequently than experienced individuals after oviposition. Host-feeding needs consideration for optimal culture.     

Antifeedant and cytotoxic activity of gibberellic acid against Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae)

The present study investigates the effect of gibberellic acid (GA3), a terpenoid and phytohormone, on the digestive physiology and intermediary metabolism of the cotton bollworm Helicoverpa armigera Hübner (Lepidoptera, Noctuidae). Incorporation of GA3 (800 μg g^?1 diet) in an artificial diet results in significant reductions in the rates of diet consumption and the efficiency of conversion of food consumption by by H. armigera larvae. The relative growth rate decreases as the concentration increases. The relative α‐amylase activity in sixth‐instar larvae of H. armigera decreases significantly after ingestion of four concentrations of GA3. Histological studies of the midgut in GA3‐treated larvae (800 μg g^?1 diet) show degeneration of the epithelial cells. The alanine and aspartate aminotransferase activity decreases at the highest concentration. However, acid phosphatase, alkaline phosphatase, γ‐glutamyl transferase and lactate dehydrogenase activity increase significantly compared with the control. The results clearly demonstrate the adverse effects of GA3 on H. armigera via interruption of nutritional physiology and metabolism.     

Helicoverpa armigera (Hübner): can wheat stubble protect cotton plants against attack?

Abstract  When investigating strategies for Helicoverpa armigera (Hübner) control, it is important to understand oviposition behaviour. Cotton ( Gossypium hirsutum ) was sown into standing wheat ( Triticum astivum L.) stubble in a closed arena to investigate the effect of stubble on H. armigera moth behaviour and oviposition. Infrared cameras were used to track moths and determine whether stubble acted as a physical barrier or provided camouflage to cotton plants, thereby reducing oviposition. Searching activity was observed to peak shortly before dawn (03:00 and 04:00 h) and remained high until just after dawn (4 h window). Moths spent more time resting on cotton plants than spiralling above them, and the least time flying across the arena. While female moths spent more time searching for cotton plants growing in wheat stubble, the difference in oviposition was not significant. As similar numbers of eggs were laid on cotton plants with stubble (3.5/plant SE ±0.87) and without stubble (2.5/plant SE ±0.91), wheat stubble does not appear to provide camouflage to cotton plants. There was no significant difference in the location of eggs deposited on cotton plants with and without stubble, although more eggs were laid on the tops of cotton leaves in wheat stubble. As the spatial and temporal distribution of eggs laid on the cotton plant is a crucial component of population stability, eggs laid on the upper side of leaves on cotton plants may be more prone to fatalities caused by environmental factors such as wind and rain. Therefore, although stubble did not influence the number of eggs laid, it did affect their distribution on the plant, which may result in increased mortality of eggs on cotton plants sown into standing wheat stubble.     

Adaptation of Helicoverpa armigera (Lepidoptera: Noctuidae) to a proteinase inhibitor expressed in transgenic tobacco

A giant taro proteinase inhibitor (GTPI) cDNA was expressed in transgenic tobacco using three different gene constructs. The highest expression level obtained was ca. 0.3% of total soluble protein when the cDNA was driven by the Arabidopsis rbcS ats1 promoter. Repeated feeding trials with Helicoverpa armigera larvae fed on clonally derived T₀ and T₁ plants expressing GTPI demonstrated that, relative to those fed on control plants, some growth inhibition (22–40%) occurs, but there was no increase in larval mortality. Proteinase activities of larvae fed on GTPI-expressing tobacco or GTPI-containing diet were examined to monitor the spectrum of digestive proteinases in the midgut. Total proteinase activity was reduced by 13%, but GTPI-insensitive proteinase activity was increased by up to 17%. Trypsin was inhibited by 58%, but chymotrypsin and elastase were increased by 26% and 16% respectively. These results point to an adaptive mechanism in this insect that elevates the levels of other classes of proteinases to compensate for the trypsin activity inhibited by dietary proteinase inhibitors.     

Arthropod Natural Enemies of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) in India

Helicoverpa armigera Hubner Lepidoptera: Noctuidae is one of the most serious insect pests in the Old World. In India, it causes substantial losses to legume, fibre, cereal oilseed and vegetable crops. This paper reviews the literature on the biology, ecology, efficacy, rearing and augmentation of endemic parasitoids and predators, as well as exotic parasitoids introduced and released in India. It also provides updated lists of H. armigera natural enemies native to India. In addition, reports of augmentative releases of Trichogramma spp., the most extensively studied natural enemy of H. armigera are summarized.     

Host-plant preference and oviposition responses of the sorghum midge, Stenodiplosis sorghicola (Coquillett) (Dipt., Cecidomyiidae) towards wild relatives of sorghum

Sorghum midge, Stenodiplosis ( Contarinia ) sorghicola (Coquillett) is an important pest of grain sorghum world-wide. Considerable progress has been made in screening and breeding for resistance to sorghum midge. However, some of the sources of resistance have become susceptible to sorghum midge in Kenya, in eastern Africa. Therefore, the wild relatives of Sorghum bicolor were studied as a possible source of new genes conferring resistance to sorghum midge. Midge females did not lay eggs in the spikelets of Sorghum amplum , Sorghum bulbosum , and Sorghum angustum compared to 30% spikelets with eggs in Sorghum halepense when infested with five midge females per panicle under no-choice conditions. However, one egg was laid in S. amplum when infested with 50 midges per panicle. A larger number of midges were attracted to the odours from the panicles of S. halepense than to the panicles of Sorghum stipoideum , Sorghum brachypodum , S. angustum , Sorghum macrospermum , Sorghum nitidium , Sorghum laxiflorum , and S. amplum in dual-choice olfactometer tests. The differences in midge response to the odours from S. halepense and Sorghum intrans were not significant. Under multi-choice conditions, when the females were also allowed a contact with the host, more sorghum midge females were attracted to the panicles of S. bicolor compared with S. amplum , S. angustum , and S. halepense . In another test, numerically more midges responded to the panicles of IS 10712 compared with S. halepense , whereas the differences in midge response to the panicles of ICSV 197 ( S. bicolor ) and S. halepense were not apparent, indicating that S. halepense is as attractive to sorghum midge females as S. bicolor . The wild relatives of sorghum (except S. halepense ) were not preferred for oviposition, and they were also less attractive to the sorghum midge females. Thus, wild relatives of sorghum can prove to be an alternative source of genes for resistance to sorghum midge.     

Genetic differentiation of Helicoverpa armigera (Hübner) and H. assulta (Guenée) (Lepidoptera: Noctuidae) based on AFLP markers

Abstract Here we use amplified fragment length polymorphism (AFLP) to assess genetic differentiation of Helicoverpa armigera and H. assulta . The results indicated that both species-specific fingerprints and cluster analysis showed the ability of AFLP technique to discriminate the two sibling species; among a total 1963 AFLP markers amplified from nine primer combinations: 777 (39.6%) were H. armigera -specific, 602 (30.7%) were H. assulta -specific, and 584 (29.7%) were common bands. The mean number of H. armigera -specific bands was significantly more than that of H. assulta -specific bands for nine primer combinations ( P < 0.05); the intraspecific distance of H. armigera and H. assulta was 0.123 0 and 0.110 7 respectively, and the interspecific distance was 0.178 3. In addition, the percentage of polymorphic loci and estimated average heterozygosity were used to estimate genetic diversity of the two species. This study therefore demonstrates that AFLP analysis is a sensitive and reliable technique to study genetic differentiation and genetic relationships between species and provides sufficient molecular markers for future linkage map construction, location and eventual cloning of genes involved in traits differentiation.     

Effect of body size and larval experience on mate preference in Helicoverpa armigera (Hübner) (Lep., Noctuidae)

Abstract:  We studied the mating selection in the cotton bollworm, Helicoverpa armigera (Hübner), in relation to body size and larval diet in the laboratory. When provided with an artificial diet at larval stage, weight, body and forewing length did not affect the probability of a male/female moth being selected for mating, but the abdominal width of selected female moths was significantly wider than that of non-selected female moths. 30 female moths were dissected and number of eggs was counted after mating, and there was a correlation between the abdominal width and egg number. There was also significant difference of weight loss between selected and non-selected male/female moths after the mating. The effect of operational sex ratio on mating latency and copulation duration were tested, and the result indicated that mating latency of male selection was significantly longer than that of female selection, but the difference of copulation duration was not significant. Cotton, corn and peanut plants were provided to larvae to test the effect of larval host plant experience on mate choice. When cotton- and peanut-fed moth severed as potential partners, both female and male of cotton-fed moths significantly preferred cotton- to peanut-fed moths for mating. The possible reasons for mate preference based on larval host plant experience may account for host plants attributes on sex pheromone variation and sexual maturity. These findings may impact Bacillus thuringiensis resistance management.     

几种植物源化合物对棉铃虫海藻糖酶活性及相关碳水化合物含量的影响

碳水化合物对昆虫的能量代谢和物质合成具有重要的作用。本研究选用2种一般性生物碱（氢溴酸东莨菪碱和烟碱）以及2种β-葡萄糖苷类化合物（七叶灵和皂角苷）, 研究其在不同浓度下对棉铃虫Helicoverpa armigera (Hübner)幼虫体内海藻糖酶活性及相关碳水化合物代谢的影响。结果表明: 用饲喂法处理3龄幼虫96 h后, 皂角苷对棉铃虫幼虫的活体抑制效果明显, 且随添加物浓度增高, 棉铃虫死亡率上升, 10, 20, 40 g/L浓度下棉铃虫的均重分别是0.194, 0.089和0.034 g, 分别为对照的86.99%, 39.91%和15.24%。对海藻糖酶活性及其相关代谢酶的测定结果表明, 2种苷类化合物显著抑制中肠海藻糖酶活性, 饲喂40 g/L皂角苷的试虫中肠海藻糖酶比活力仅是对照组的54.21%; 饲喂30 g/L七叶灵的试虫中肠海藻糖酶比活力为对照组的83.73%。而2种生物碱类化合物显著抑制血淋巴和脂肪体中海藻糖酶活性, 20 g/L氢溴酸东莨菪碱对棉铃虫血淋巴和脂肪体组织的海藻糖酶活性抑制率分别为7.24%和71.43%; 而20 g/L烟碱对试虫血淋巴和脂肪体组织的海藻糖酶活性抑制率为26.29%和33.44%。用氢溴酸东莨菪碱、 烟碱和七叶灵处理试虫后, 血淋巴海藻糖含量都有所增高。4种化合物能够导致试虫糖原磷酸化酶活性变化, 其中, 皂角苷在中肠和脂肪体表现为显著抑制作用, 而随外源化合物浓度变化, 糖原含量和糖原磷酸化酶活性表现为此消彼长关系。饲喂4种植物源化合物的试虫血淋巴中葡萄糖浓度变化和其海藻糖变化一致。本研究证明β-葡萄糖苷类化合物是海藻糖酶抑制剂, 在作为先导化合物进行农药创制开发方面具有重要意义。