Cereal leaf beetle (Oulema melanopus (L.)) population densities and winter wheat yields

Grain yields of a soft white winter wheat cultivar, cv. Ionia, susceptible to cereal leaf beetle (Oulema melanopus (L.)), were determined when the crop was subjected to four controlled infestation levels of the beetle in caged plots over a 3-year period in Michigan. Although identical infestation procedures and insect numbers were used each year, the intensity of larval infestation and feeding damage varied with the year. Significant (P < 0·01) grain losses occurred in plots that had at least 9·0 larvae per stem. The greatest yield loss was 45% and occurred with 15 larvae per stem and 85% feeding damage. Beetle damage had a greater effect on kernel weight than on the other yield components. Although economic thresholds should be conservative to allow for environmental variations, it appears that soft white winter wheat can often withstand beetle infestation levels greater than the current economic threshold of three or more eggs and largae per stem before the boot stage or one or more large larvae per flag leaf during heading.     

The effect of some invertebrate species on the growth of white clover (Trifolium repens L.) in the lahoratory

In laboratory experiments to clarify earlier field observations, Sitona lepidus larvae caused significant damage to established clover plants at infestations of approximately 1–2 per plant. When eggs were placed on the soil, cultivars of differing cyanogenic capacity were damaged equally. The plants did not recover when larval feeding ended.
Leatherjackets, slugs and 'lucerne flea' fed most on the least cyanogenic cultivars, even where no choice was offered. Plants ultimately recovered from damage by leatherjackets. Deroceras reticulatum caused more damage than did Arion fasciatus. The proportion of leaves damaged by lucerne fiea was highest in the least cyanogenic eultivar but also tended to increase in the most cyanogenic cultivar, confirming a field observation. At high population densities lucerne flea was capable of killing some seedlings but was not tested against established plants.     

The phytotoxicity of insecticidal seed coatings and granular and spray soil treatments to grain yields in field experiments on the control of larvae of wheat bulb fly (Delia coarctata Fall.)

A simple statistical procedure has been derived to measure the direct effect of insecticides, particularly any phytotoxic effect, on cereal grain yields. Data from several years' field experiments on the use of insecticides to control larvae of the wheat bulb fly (Delia coarctata Fall.) (Diptera: Anthomyiidae) have been used to determine the ratio of (grain yield ÷ percentrage of undamaged shoots) for plots treated with an insecticide to (grain yield ÷ percentage of undamaged shoots) for untreated plots. A ratio < 1 indicated that the insecticide was phytotoxic; a ratio > 1 suggested that the compound was phytostimulant. The ratios of all the insecticidal seed coatings and soil treatments of granules and sprays which were tested in the field experiments have been measured. The ratios for all insecticides (apart from fonofos microencapsulated seed coating at one site in 1974–1975) were <1. The phytotoxicity of the insecticides was found to vary between years. Insecticidal soil treatments (granules and sprays) seemed to be as phytotoxic as seed coatings. Synthetic pyrethroid seed coatings were slightly less phytotoxic than organophosphorus seed coatings. In field experiments on the control of wheat bulb fly larvae by insecticides, phytotoxicity has usually been estimated by a subjective system of scoring plots visually before larval invasion of plants. This method was compared with the objective method of determining pesticide/untreated (or P/U) ratios. Visual scoring appears to be the more efficient method of determining the most phytotoxic insecticide, whereas the least phytotoxic insecticide is determined more accurately by the method of P/U ratios.     

Seasonal distribution of stem-boring larvae including frit fly (Diptera: Oscinella frit L.) and pest damage in perennial ryegrass

Changes in the population of stem-boring Dipterous larvae (including Oscinella frit ) were examined weekly for a year on plots of perennial ryegrass ( Lolium perenne cv. S24). The herbage net regrowth rate of these plots and of plots receiving the pesticide, phorate, was also monitored. Herbage net regrowth rates were greatest in April and October. At the same times the differences in net regrowth between treated and untreated plots were greatest, thus indicating the periods of the greatest loss of production due to pest damage to the sward.
Populations of stem-boring larvae fell below 100 m⁻² for only 4 weeks in the year and were maximal in autumn and early winter. Larval mortality exceeded 50% during the winter period. A correlation was found between larval activity and sward damage.     

Effects of pesticides and fertilizer on invertebrate populations of grass and wheat plots in Kent in relation to productivity and yield

At a site in Kent, perennial ryegrass (Lolium perenne) variety S24 and Italian ryegrass (L. multiflorum) variety RVP, wheat varieties Armada and Norman, and the original mixed grass ley were grown in small plots during 1982–84. Two toxic pesticides (phorate and aldicarb) were applied to half the total number of plots three times each year to eliminate soil invertebrate populations. Fertilizer was also applied to most plots. The yields of the crops, grown with and without pesticide, and the effects of the fertilizer were compared. Grass herbage yield was measured on three occasions during the summers of 1983 and 1984. Wheat grain yields were also determined in 1983. During the first year significant differences were not apparent in grass dry matter yield between pesticide-treated and non-treated plots, but significant differences were found in the second year. The perennial ryegrass was more susceptible to pest damage than the Italian ryegrass or the grass ley. Grass yields varied between cuts and in relation to variety and pesticide treatment, yields tending to be greater in untreated plots. Fertilizer treatment greatly increased grass dry matter yields, particularly with the Italian ryegrass. The effects of pesticide treatment on both wheat varieties varied although some yield enhancement was evident. Invertebrate animal populations in pesticide and fertilizer-treated plots were also assessed in autumn 1982, spring and autumn 1983 and spring 1984. In contrast to pesticide treatment, fertilizer treatment had little effect on soil invertebrate populations. Nematode populations were reduced at each sampling occasion by the pesticide treatment. Slug populations were initially unaffected but were subsequently reduced. Leatherjackets, by far the most abundant pest in both grass and wheat plots, were markedly affected by pesticides on all sampling occasions. Generally, fewer soil-dwelling dipterous larvae were recovered in spring than in autumn. Stem-boring dipterous larvae were virtually absent.     

The effect of some invertebrate species on persistence of white clover in ryegrass swards

In two experiments in established swards of perennial ryegrass and white clover, plots were treated with pesticides to control slugs, leather-jackets, weevil larvae and lucerne flea as selectively as possible. Other plots were treated to control ail of these pests.
Chlorpyrifos application in early summer (to control weevil larvae) and methiocarb pellets (to control slugs) also gave partial control of leather-jackets. Other effects on non-target species were considered to be unimportant, as pest status could not be attributed to the species. A high level of control of lucerne flea by methiocarb pellets, noted previously, was confirmed.
At both sites combined treatment against insect pests and slugs produced large increases in clover content and yield over a 3-year period, in comparison with untreated plots, although clover tended to decline In alt plots. At one site, where the clover content of untreated plots reached 33% at one stage, specialist clover herbivores such as weevils and lucerne flea were more common. Treatments directed against weevils and slugs gave the highest clover yields, and leatherjacket control may also have contributed, particularly when the population reached 0.9 m ha⁻¹ in the final year. At the other site, where the clover content was low (ultimately 01.1–6%), leather-jacket populations reached 2.1 m ha⁻¹ and slug numbers were also relatively high. Control of these species contributed most to the relative increase in clover content and yield.     

Effect of the formamidine insecticide chordimeform on feeding and reproduction in the noctuid moth,Spodoptera littoralis (Boisduval)

The sub-lethal effects of the formamidine insecticide chlordimeform on feeding and reproduction in the noctuid moth, Spodoptera littoralis, have been examined. By measuring changes in larval weight, chlordimeform hydrochloride was found to reduce food consumption significantly (by 25–64%) in fifth-instar larvae during a 48h period when incorporated at a rate of 0·1–10mg/g of artificial diet. Although no mortality was observed during larval feeding, considerable mortality occurred during pupation and subsequent emergence of the adult from the pupae. The compound also significantly reduced larval feeding by 22–28% compared with the control, when topically applied to fifth-instar larvae. Egg laying in female moths was reduced by at least 88% when chlordimeform was topically applied at a concentration of 1 or 10 μg/moth. Disruption of various components of normal egg-laying behaviour was also observed. The results are discussed in relation to recent evidence that, in addition to a direct killing action, chlordimeform induces abnormal changes in insect behaviour, especially during critical points in the life cycle, which may contribute to the protection of plants from insect attack.     

Susceptibility of imidacloprid-resistant Colorado potato beetles to non-neonicotinoid insecticides in the laboratory and field trials

Repeated use of neonicotinoid insecticides has resulted in the first reported cases of Colorado potato beetle (Leptinotarsa decemlineata (Say)) resistance to imidacloprid. In the laboratory we determined susceptibility of the imidacloprid-resistant Colorado potato beetles from a population in Southern Maine to other insecticides currently registered for use on potato. This population was about 30-fold resistant to imidacloprid and could not be effectively controlled by its applications. Control mortality was significantly higher for the imidacloprid-resistant larvae than for the susceptible larvae, suggesting that fitness disadvantages may be associated with the resistance trait. Resistant larvae exhibited significantly less mortality than susceptible larvae when exposed to cyfluthrin, carbaryl, azinphosmethyl, and methamidophos. Their susceptibility to oxamyl was also somewhat reduced, although it did provide nearly 100% mortality at the highest concentration tested. Disulfoton was highly toxic to the resistant larvae. Oxamyl killed about 40% of the adults in greenhouse assays with potted potato plants, altered their feeding behavior (fewer adults up on plants), and reduced defoliation by more than 90%. Disulfoton was not lethal to adults, but significantly suppressed their feeding. In field trials with the resistant population, oxamyl and imidacloprid + spinosad provided the best beetle control. Novaluron had no detectable effect on beetle densities. There was little difference between the plots treated with imidacloprid or thiamethoxam and the untreated control. Our results suggest that insecticide rotation may be a valuable option for managing imidacloprid-resistant Colorado potato beetle populations. We also had a good consistency between the results of the Petri dish, greenhouse, and field experiments, indicating that screening under laboratory confinement may be useful when developing initial recommendations to potato growers in areas affected by resistance to neonicotinoids.     

Non-target effects of the ‘push–pull’ habitat management strategy: Parasitoid activity and soil fauna abundance

We assessed the non-target effects of a habitat management system (‘push–pull’) on maize stemborer specialist natural enemy activity and soil Collembola. Two study sites in western Kenya were sampled. There were two treatments at each site, maize monocrop and ‘push–pull’. The latter comprised an intercrop of maize and Desmodium, Desmodium uncinatum Jacq., with Napier grass, Pennisetum purpureum (Schumach), as a trap crop planted around the edge of the plot (spaced 1 m from main crop). Trichogramma spp. were recovered from stemborer eggs while Cotesia sesamiae and Cotesia flavipes were recovered from stemborer larvae, and Dentichasmias busseolae from pupae. Mean number of eggs parasitized was significantly higher in the maize monocrop than in the ‘push–pull’ plots however proportions parasitized did not differ between the two systems. The number of larvae and pupae parasitized and dead from causes other than parasitism similarly did not differ between cropping systems. Proportions of larvae and pupae parasitized were significantly higher in the ‘push–pull’ than in the monocrop plots, indicating that the activity of larval and pupal parasitoids was enhanced. C. sesamiae female wasps were attracted to the volatiles from Desmodium flowers but not those from the leaves in a four-arm olfactometer bioassay. A total of 1530 individual Collembola in seven families were recovered from the plots. The ‘push-pull’ strategy did not have any significant effect on Collembola abundance and dominance. The factors underlying these observations and their implications are discussed.     

Effects of pigment glands and gossypol on growth,development and insecticide-resistance of cotton bollworm (Heliothis armigera (Hübner))

Cotton bollworm (Heliothis armigera) is a major pest of cotton and other crops. It is important to understand the mechanisms of insecticide tolerance of cotton bollworm on cotton cultivars with host plant resistance to this insect pest. The objectives of this study were to investigate the effects of cotton pigment glands and their gossypol on the growth, development and insecticide tolerance of cotton bollworm. Three pairs of cotton isogenic lines with glanded versus glandless leaves, as well as artificial diets with 5 levels of gossypol, were used to raise cotton bollworm larvae for five generations. The growth, development and insecticide tolerance of larvae were studied. The results indicated that the cotton pigment glands and higher levels of gossypol resulted in a significant decrease in larval weights and moth eclosion rates and delayed the development of larvae and pupae. Larvae that fed on glanded cotton leaves were significantly more tolerant to two insecticides, cyhalothin and monocrotophos, than those fed on glandless cotton leaves. LD₅₀ values were only increased where they were in amount per unit body weight, and not where were calculated in amount per individual. Also the insecticide tolerance of cotton bollworm larvae increased as the gossypol content was raised from 0 to 0.225% in artificial diets. Meanwhile, the activities of two detoxifying enzymes, carboxylesterase and glutathione s-transferase, were significantly higher in the larvae fed on glanded cotton leaves than those fed on glandless cotton leaves. The activities of two enzymes also increased greatly with the increase of gossypol content from 0 to 0.225% in artificial diets. Across 5 generations of feeding and investigation, the significant inhibition effect on larval growth and larval tolerance to two pesticides were found to be only associated with the feeding by current generation, but were not related to previous diets. The activities of two detoxifying enzymes in larvae were also not enhanced significantly when they were fed continuously on glanded cotton leaves or artificial diet with high gossypol. These results indicated that pigment glands and higher levels of gossypol not only inhibited the growth of cotton bollworm larvae but also enhanced their insecticide tolerance. However, the inhibition effect and enhanced insecticide tolerance were inducible but could not be accumulated or inherited. These results will help us better understand the interaction and co-evolution of insecticide tolerance in larvae of cotton bollworm and host chemical components, and also has provided useful information on cotton bollworm management in cotton production, especially in glandless cotton.     

Honey Bee (Hymenoptera: Apidae) Nursing Responses to Cuticular Cues Emanating from Short-term Changes in Larval Rearing Environment

Honey bee larvae are dependent on the social structure of colony for their provisioning and survival. With thousands of larvae being managed collectively by groups of foragers (collecting food resources) and nurse bees (processing food and provisioning larvae), coordination of colony efforts in rearing brood depends on multiple dynamic cues of larval presence and needs. Much of these cues appear to be chemical, with larvae producing multiple pheromones, major being brood ester pheromone (BEP; nonvolatile blend of fatty acid esters) that elicits both short-term releaser effects and long-term primer effects. While BEP can affect colony food collection and processing with the signaling of larval presence, it is unclear if BEP signals individual larval needs. To understand this aspect, in a series of experiments we manipulated larval feeding environment by depriving larvae from adult bee contact for 4-h period and examined (1) nurse bee interactions with contact-deprived and nondeprived larvae and larval extracts; (2) forager bee responses to contact-deprived and nondeprived larval extracts. We also characterized BEP of contact-deprived and nondeprived larvae. We found that nurse honey bees tend to aggregate more over contact-deprived larvae when compared with nondeprived larvae, but that these effects were not found in response to whole hexane extracts. Our analytical results suggest that BEP components changed in both quantity and quality over short period of contact deprivation. These changes affected foraging behavior, but did not appear to directly affect nursing behavior, suggesting that different chemical cues are involved in regulating nursing effort to individual larvae.     

草地贪夜蛾有转移危害茶树的可能

草地贪夜蛾（Spodoptera frugiperda）是世界性的重大迁飞性害虫,寄主范围极广。本文比较研究了草地贪夜蛾幼虫取食茶树和玉米叶片的生长适合度。试验结果表明,饲喂茶树叶片的初孵草地贪夜蛾幼虫8 d死亡率高达100%。3龄（9日龄）草地贪夜蛾幼虫取食茶树叶片的幼虫体重增长量显著低于以玉米叶为食的幼虫;取食3 d和6 d后,以茶树叶片为食的草地贪夜蛾幼虫的体重分别是以玉米叶为食的幼虫体重的35.58%和36.67%。取食茶树叶片的草地贪夜蛾幼虫的生长适合度明显低于取食玉米叶的幼虫。主要表现为：（1）8 d后,取食玉米叶的草地贪夜蛾3龄幼虫存活率比取食茶树叶片的幼虫高出20%;（2）取食茶树叶片的草地贪夜蛾幼虫的成功化蛹率为54.17%;（3）取食茶树叶片的草地贪夜蛾幼虫的发育历期极显著长于取食玉米叶的幼虫,且蛹重、蛹长和蛹宽极显著低于取食玉米叶的幼虫的蛹。尽管取食茶树叶片的草地贪夜蛾幼虫的生长适合度较低,但是由于茶园中存在草地贪夜蛾嗜食的杂草,初孵幼虫可以杂草为食,3龄以上幼虫可取食茶树叶片并成功化蛹。因此,推测一旦草地贪夜蛾误迁入茶园,在茶园中的嗜食杂草被其食光后,其幼虫很有可能进一步危害茶树。     

Biology,seasonal occurrence,host range and damage potential of the castor hairy caterpillar,Euproctis lunata Walk. (Lymentriidae : Lepidoptera)

The castor hairy caterpillar, Euproctis lunata Walk. in Bangladesh has six larval instars that averaged 3·3 ± 0·07, 3·5 ± 0·08, 3·7 ± 0·11, 4·7 ± 0·12 and 5·0 ± 0·15 days respectively; 204 ± 6·5 eggs were laid per female; 97·2 ± 0·37 eggs hatched. Male and female moths lived 4·00 ± 0·16 and 4·45 ± 0·13 days, respectively. Most larvae were found in September and October with castor the most preferred host. The fifth- and sixth-instar larvae consumed more leaves than did those of the first four instars. When larvae were released on plots there were subsequently fewer late-instar larvae where most had been released. Yields were significantly reduced if there were two or more larvae per plant.     

Rice striped stem borer, Chilo suppressalis (Lepidoptera: Pyralidae), overwintering in super rice and its control using cultivation techniques

Super rice has the potential to deliver very high yields but is also susceptible to attack by the striped rice stem borer, Chilo suppressalis. In this study, surveys and field trials were performed to examine this problem and efficient ways were found to lower the borer’s population density. It was found that larger super rice plants provided more refuges for borers to evade insecticide contact and had a longer growth period allowing borers to complete their larval development in an intact environment. The current cultivation regime was shown to favour outbreaks of borers. Super rice is harvested leaving tall field stubbles until the following growing season, thus providing food and cover in which borers may successfully overwinter. We found that borer larvae were distributed to a greater height in the plants of super rice than in common rice, making control through agricultural operations more feasible. Burning fields after harvest, which killed 84.5% of borers, seemed the best remedy, though this practice is forbidden in China for ecological reasons. Leaving short stubbles followed by appropriate treatment of the rice straw killed 74.0% of the borer population. In addition, spring irrigation after the pre-pupation dispersal movements of borers killed more than half of the overwintering population. Pre-winter rotary tillage had little effect on borer numbers but enhanced the population reduction effect of irrigation the following spring. Based on the results obtained, efficient control of borers on super rice can be achieved by harvesting leaving short stubbles, followed by rotary tillage and spring irrigation. This regime can reduce the borer population by more than 98%, minimising chemical use and maximising use of a reduced agricultural workforce.     

Pest-damage relationships for Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) on vegetative soybean

The response of vegetative soybean (Glycine max) to Helicoverpa armigera feeding was studied in irrigated field cages over three years in eastern Australia to determine the relationship between larval density and yield loss, and to develop economic injury levels. Rather than using artificial defoliation techniques, plants were infested with either eggs or larvae of H. armigera, and larvae allowed to feed until death or pupation. Larvae were counted and sized regularly and infestation intensity was calculated in Helicoverpa injury equivalent (HIE) units, where 1 HIE was the consumption of one larva from the start of the infestation period to pupation. In the two experiments where yield loss occurred, the upper threshold for zero yield loss was 7.51 ± 0.21 HIEs and 6.43 ± 1.08 HIEs respectively. In the third experiment, infestation intensity was lower and no loss of seed yield was detected up to 7.0 HIEs. The rate of yield loss/HIE beyond the zero yield loss threshold varied between Experiments 1 and 2 (−9.44 ± 0.80 g and −23.17 ± 3.18 g, respectively). H. armigera infestation also affected plant height and various yield components (including pod and seed numbers and seeds/pod) but did not affect seed size in any experiment. Leaf area loss of plants averaged 841 and 1025 cm²/larva in the two experiments compared to 214 and 302 cm²/larva for cohort larvae feeding on detached leaves at the same time, making clear that artificial defoliation techniques are unsuitable for determining H. armigera economic injury levels on vegetative soybean. Analysis of canopy leaf area and pod profiles indicated that leaf and pod loss occurred from the top of the plant downwards. However, there was an increase in pod numbers closer to the ground at higher pest densities as the plant attempted to compensate for damage. Defoliation at the damage threshold was 18.6 and 28.0% in Experiments 1 and 2, indicating that yield loss from H. armigera feeding occurred at much lower levels of defoliation than previously indicated by artificial defoliation studies. Based on these results, the economic injury level for H. armigera on vegetative soybean is approximately 7.3 HIEs/row-metre in 91 cm rows or 8.0 HIEs/m².     

Effect of imidacloprid and fipronil pesticide application on Sympetrum infuscatum (Libellulidae: Odonata) larvae and adults

The effect of imidacloprid and fipronil on Sympetrum infuscatum larvae and adults during the rice cultivation period was monitored using an experimental micro-paddy lysimeter (MPL) system. Twenty-two hatched larvae were laid on the soil surface of each MPL. MPLs were treated with imidacloprid, fipronil, and the control MPL was left untreated. The pesticide concentration, S. infuscatum larval and adult populations, and larval emergence time were monitored in each MPL. The maximum imidacloprid and fipronil concentration in paddy water was 52.8 μg/l at 1 day, and 1.3 μg/l at 6 h, respectively, after the pesticide application. Both pesticides dissipated quickly in paddy water, with half-lives of 8.8 and 5.4 days for imidacloprid and fipronil, respectively. The absence of S. infuscatum larvae and exuviae in the fipronil-treated MPL was remarkable. The larval survival decreased to 63.6 ± 18.2, 15.2 ± 2.6, and 0% in the control, imidacloprid-treated, and fipronil-treated MPLs, respectively, by 9 days after pesticide application. Emergence in the imidacloprid-treated MPL was also significantly lower than that in the control MPL. The observed decrease in the abundances of S. infuscatum larvae and adults in MPLs seems to be both directly and indirectly associated with nursery-box application of fipronil and imidacloprid.     

Mechanical interaction between larvae of the Colorado potato beetle and glandular trichomes ofSolanum berthaultii Hawkes

The rate of accumulation of glandular trichome exúdate ofSolanum berthaultii on the tarsi of Colorado potato beetle (Leptinotarsa decemlineata) larvae depended on larval size (instar), with large larvae bearing the hardened, darkened exudate on more of their tarsi than did small larvae. In greenhouse studies, third instar larvae accumulated large amounts of exudate regardless of which of 2S. berthaultii accessions they were exposed to, but exudate accumulation by first instars was influenced significantly by plant accession. Tarsal accumulation of exudate was lower in field plots of bothS. berthaultii accessions, but tended to increase with time of exposure. The significant differences in exudate accumulation among larvae exposed to the 2 accessions in the greenhouse were not evident in the field. The density of type A glandular trichomes on the abaxial leaflet surface differed significantly between the 2 accessions in both greenhouse and field. Despite these effects of host and environment on the accumulation of readily observed amounts of trichome exudate on larval tarsi, no larvae were trapped by the adhesive exudate.     

稻纵卷叶螟对不同植物的产卵趋性与取食选择

【目的】稻纵卷叶螟是我国水稻上的一种重要害虫,在田间除水稻之外还可取食多种禾本科植物并完成生活史,但在大发生年份该虫几乎只在水稻上发生。本研究旨在明确该虫在水稻及其他寄主植物上的产卵选择及后代取食趋性的机制。【方法】采用室内笼罩选择实验比较了稻纵卷叶螟在水稻、玉米、稗草、狗尾草上的产卵与取食选择性以及取食经历对产卵、取食选择的影响。【结果】在笼罩条件下稻纵卷叶螟成虫在水稻叶片上的着卵量占总卵量的49.08%,显著高于其他三种植物;幼虫取食水稻后发育历期为17.29 d,显著短于取食玉米和狗尾草,同时取食水稻后蛹重最重;幼虫期分别取食水稻和玉米的稻纵卷叶螟成虫对四种植物的产卵选择无变化,仍显著偏好选择水稻产卵;低龄幼虫的取食选择性在几种植物之间无显著差异,低龄期取食水稻的幼虫发育到3龄、4龄后对寄主的取食选择顺序为狗尾草水稻、稗草玉米;低龄期取食玉米的幼虫发育到3龄、4龄后对寄主的取食选择为狗尾草玉米水稻、稗草。【结论】稻纵卷叶螟成虫显著偏好在水稻上产卵,产卵选择性不受幼虫取食经历影响,产卵选择性与幼虫的取食选择性并不一致。幼虫取食水稻的发育历期最短,蛹重最高。高龄幼虫显著偏好取食狗尾草,同时,低龄期的取食经历改变了高龄幼虫对水稻和玉米的取食偏好。     

玉米抗螟性室内鉴定新技术──虫粪圈法

室内抗螟性离体鉴定，采用虫粪圈法测定根据粪圈系数大小确定玉米抗螟性的强弱，凡系数大，幼虫发育良好，虫体重，且田间心叶期鉴定验证，食叶级别亦高，抗螟性差．系数与幼虫体重、与田间食叶级别均是显著正相关。比室内离体鉴定幼虫秤体重法，简便易行．不需要电子天平，更具有广泛的实用性．     

杂交早稻不同生育期对叶面损伤的反应：稻纵卷时螟危害的田间模拟试验

A field trial was conducted under natural ecological conditions and regular management to evaluate the effect of the rice leaffolder, Cnaphalocrocis medinalis, damage on the yield of early-season hybrid rice (Shanyou 402) by artificial defoliation. Foliar area of plants were cut off at the rate of 5%-30% at early tillering, peak tillering, elongation, booting, and milky stage, respectively, with each treatment including four 1 m² replications. The average yields from the plots defoliated at peak tillering were significantly higher than that of the control whereas the yields from the plots defoliated at the milky stage were lower than that of the control. Thus, the hybrid plants were apparently tolerant to foliar injury at tillering. This indicates that the current control thresholds recommended for the leaffolder should be reevaluated and that no spray one month after transplanting should be an acceptable practice for the strategy of the leaffolder control.