Effects of neem-based insecticides on beet armyworm （Lepidoptera： Noctuidae）

Abstract Three commercial neem [ Azadirachta indica A. Juss (Meliaceae)]-based insecticides, Agroneem, Ecozin, and Neemix, and a non-commercial neem leaf powder, were evaluated for oviposition deterrence, antifeedant effect on larvae, and toxicity to eggs and larvae of the beet armyworm, Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae), on cotton leaves in the laboratory. Oviposition deterrence in no-choice, and two- and fivechoice assays, was observed for the neem-based insecticide treatments when compared with a non-treated control. Neem-based insecticides also deterred feeding by beet armyworm larvae. Direct contact with neem-based insecticides decreased the survival of beet armyworm eggs. Survival of beet armyworm larvae fed for 7 days on leaves treated with neembased insecticides was reduced to 27, 33, 60, and 61% for neem leaf powder, Ecozin, Agroneem, and Neemix, respectively. Possibilities for adoption of neem-based insecticides in commercial cotton for beet armyworm control are discussed.     

Reproduction-flight relationship in the beet armyworm, Spodoptera exigua (Lepidoptera: Noctuidae)

To evaluate the relationship between reproduction and migratory flight, we examined ovaries, tethered flight, and egg laying in the beet armyworm, Spodoptera exigua (Hübner). Ovarian development in female S. exigua was classified into five stages in relation to the postemergence age of the moths. Oviposition peaked at ovarian stages III and IV. Mating accelerated ovarian development in this species, and thus the mated females developed faster than the virgin moths in ovaries. In virgin adults, flight capacity increased from the first day to the third day after emergence and remained at a high level until the moths were 7 d old. In contrast, the mated moths reached the maximum flight capacity in 2 d after emergence and maintained a high level until the age of 7 d. However, mating status could not influence the flight capacity of the beet armyworm, although there were general differences in flight capacity between virgin and mated adults at the same age. Moreover, significant correlations between the number of eggs laid and the flight capacity were not performed by the mated moths. These results showed that mating status and ovarian development did not seem to influence flight capacity in the beet armyworm, which was not in agreement with the definitions of the oogenesis-flight syndrome observed in many other migratory insects.     

Acid and alkaline phosphatase activity in the fat body and midgut of the beet armyworm,Spodoptera exigua (Lepidoptera: Noctuidae), infected with nuclear polyhedrosis virus

Changes in the activity of acid and alkaline phosphatase in Spodoptera exigua larvae infected with nuclear polyhedrosis virus have been investigated. Three days after per os infection, the activity of acid phosphatase in the fat body and midgut of infected larvae was significantly higher than that in normal larvae. Alkaline phosphatase activity did not show such significant changes. There were differences in the phosphatase patterns depending on whether their activities were expressed as enzyme units per milligram of fresh organ weight or per milligram of homogenate protein. The literature relevant to the subject allows us to conclude that the increase in phosphatase activities in S. exigua larvae is not specifically associated with virus infection itself, but, rather, is a reaction of the insect organism to the diminishing supply of energy sources.     

自同安钮夜蛾幼虫分离的一种核型多角体病毒

对在林间导致同安钮夜蛾Anua indiscriminate Moore幼虫死亡的一种病原物进行了分离和鉴定,并对该病原物进行了室内毒力测定。结果表明：该病原物为核型多角体病毒, 定名为同安钮夜蛾核型多角体病毒(AiNPV)。其对同安钮夜蛾幼虫的致死浓度LC₅₀和LC₉₀分别为3.4×10⁴和3.8×10⁷ PIB/mL。     

Foliar persistence and residual activity of methoxyfenozide against beet armyworm (Lepidoptera: Noctuidae)

A greenhouse study was conducted to investigate the persistence of methoxyfenozide in pepper (Capsicum annuum L.) foliage. An aqueous suspension of methoxyfenozide was sprayed on pepper plants at concentrations of 72 and 144 mg of active ingredient (a.i.)/L. Foliage was collected at different intervals of time (0, 3, 5, 10, 20, 30, 40, and 50 days) after the treatment, and the methoxyfenozide residue was measured by high‐performance liquid chromatography. The foliage was also used in bioassays to determine the residual toxicity on and the consumption rate of the third‐instar larvae of the beet armyworm, Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae). The methoxyfenozide concentrations observed after 50 days had decreased to 19 and 69 μg/g per sample, corresponding to a loss of 61% and 28% from the application concentrations of 72 and 144 mg a.i./L, respectively. When fitting a first‐order kinetics degradation model, the half‐life (DT₅₀) of this compound was 76 days. Both application concentrations of methoxyfenozide caused a high mortality rate (≥97%) when the larvae were fed the pepper foliage collected at all of the time intervals. Lastly, at all of the time points, the consumption rate by the larvae was reduced to between 57% and 92% for both concentrations that were bioassayed. Our results indicate that, under the present greenhouse conditions, the degradation of methoxyfenozide was slower than that reported by other authors and that its residues were highly toxic to S. exigua larvae. The implications of these results for the management programs of this pest are discussed.     

甜菜夜蛾交配行为和能力

在(27±1)℃,光周期L14∶D10的条件下对甜菜夜蛾I>Spodoptera exigua的交配行为及能力进行了研究。结果表明：成虫在羽化当晚即可进行交配,交配率以羽化后头三个晚上的较高(>82%),但从第4天起则显著下降。成虫一天中的交配时间出现于23:30～05:30之间,交配高峰出现在01:30～02:30和03:00～04:00 之间, 其中以第1高峰的发生频率较高。成虫交配持续时间从22～191 min不等,但以30～60 min的为多(40.8%, n=97), 60～90 min的次之(19.4%),超过180 min的较少(10.2 %)。另外,交配持续时间与蛾龄紧密相关。蛾龄越大,交配持续的时间越长,且差异显著。雄蛾一生的交配能力由1～11次不等,但受性比的影响显著：在性比为1∶1的条件下,雄蛾平均交配次数仅为3.0 次,而在2♀∶1♂至5♀∶1♂时,则增加到5.1～6.0 次。雌蛾交配比例及次数受性比的影响也很大：没有交配的雌蛾比例从1∶1时的8.3%增加到5♀∶1♂时的32%,仅交配一次的比例从16.7%增加到38.7%,而交配≥5 次的比例则从 25%下降到0。最后,对这些结果在甜菜夜蛾防治中应用的可能性进行了讨论。     

Relative effects of ultraviolet and visible light on the activities of corn earworm and beet armyworm (Lepidoptera: Noctuidae) nucleopolyhedroviruses

Five different combinations of fluorescent tubes (UV-B/UV-B, UV-B/UV-A, UV-A/ UV-A, UV-B/White, White/White) were used to determine relative effects of UV and visible light on the nucleopolyhedroviruses (NPV) of Helicoverpa zea and Spodoptera exigua. For both viruses, the greatest inactivation occurred with exposure to UV-B radiation. Both virus concentration and radiation exposure time influenced the rate and degree of inactivation. In the case of the UV-A/UV-A and White/White combinations inactivation occurred only with the longest exposure (24 h) and the lowest virus concentration (0.747 PIB/mm2). The NPV from H. zea was found to be more sensitive to UV radiation than the NPV from S. exigua.     

Enhancement in activity of homologous and heterologous baculoviruses infectious to beet armyworm (Lepidoptera: Noctuidae) by an optical brightener

The nuclear polyhedrosis virus (NPV) from the beet armyworm, Spodoptera exigua (Hübner) (SeMNPV), was the most active virus tested against the beet armyworm (LC50 = 4.1 PIBs/mm2), followed by nuclear polyhedrosis viruses from the alfalfa looper, Autographa californica (Speyer) (AcMNPV; LC50 = 92.6 PIBs/mm2), and the celery looper, Anagrapha falcifera (Kirby) (AfMNPV; LC50 = 195.7 PIBs/mm2). In the case of the nuclear polyhedrosis virus from the bollworm, Helicoverpa armigera (Hübner), LC50s could only be obtained for five/six replicates, whereas LC50s could only be obtained for two/six replicates for the nuclear polyhedrosis virus from the wax moth, Galleria mellonella (L.) (GmMNPV). When an optical brightener Tinopal LPW was added to virus suspensions, LC50 values were reduced by 130-fold for both SeMNPV and AcMNPV and by 300-fold for AfMNPV. The addition of Tinopal LPW greatly increased the activities of HaMNPV and GmMNPV. In terms of speed of kill, Tinopal LPW reduced the LT50s for all nuclear polyhedrosis viruses by 30-40%.     

甜菜夜蛾核型多角体病毒在宿主种群中的垂直传播研究

以两种浓度的病毒液感染甜菜夜蛾4龄、5龄幼虫,以研究甜菜夜蛾核型多角体病毒从亲代到子代垂直传递的方式和效率。实验结果表明,该病毒可通过母体介导(卵内、卵表)和父体介导等3种方式传递给子代,造成子代感染。幼虫经口感染后母体介导传递实验表明,病毒垂直传播可引起20%～48%的子代幼虫病死,并能使子代成虫产卵量下降;母体介导传播实验中,以5%福尔马林进行卵表面消毒证实仍有18.8%的幼虫感染病毒死亡,表明了该病毒可经卵内传播,并同时存在着附卵传播;母体介导传递实验还表明病毒对宿主有弱化作用,亲代免于病死的蛹重量减轻,羽化所得雌成虫的产卵量下降,产卵期延长。以交互配对将感染与未感染的雌雄成虫彼此交配,表明雄成虫精子也能垂直传递病毒(父体介导),引起20％～40%子代幼虫感病死亡。成虫经口感染,对所产卵块表面消毒后,仍导致28.6%的子代幼虫死于病毒感染,也表明存在卵内传播。     

Effects of virus concentration and ultraviolet irradiation on the activity of corn earworm and beet armyworm (Lepidoptera: Noctuidae) nucleopolyhedroviruses

Laboratory studies were initiated to determine the relationship between virus concentration and radiation-caused inactivation of NPVs from Helicoverpa zea (HzSNPV) and Spodoptera exigua (SeMNPV). In the laboratory, a UV-B/UV-A system was used for inactivation studies. For both viruses inactivation was dependent upon both length of UV exposure and virus concentration. At all virus concentrations HzSNPV was more sensitive to UV than SeMNPV. In the field HzSNPV was used and virus persistence was significantly affected by virus concentration (i.e., inactivation was inversely related to virus concentration).     

An insensitive acetylcholinesterase confers resistance to methomyl in the beet armyworm Spodoptera exigua (Lepidoptera: Noctuidae)

Two forms of acetylcholinesterase were identified in field populations of the beet armyworm, Spodoptera exigua (Hübner), collected from cotton in San Joaquin Valley, CA. Strains (BESS and BKRR) homogeneous for each variant were isolated and their relative susceptibilities to methomyl, chlorpyrifos, and chlorpyrifos-oxon assessed by topical application bioassay. In comparisons with a laboratory susceptible strain (DOW), BKRR and BESS expressed 68-fold and sevenfold resistance, respectively, to the carbamate methomyl. Neither strain was cross-resistant to chlorpyrifos or its oxygen analog (chlorpyrifos-oxon). In biochemical studies, the BKRR AChE enzyme was approximately 30-fold and sixfold more insensitive to methomyl and chlorpyrifos-oxon, respectively, compared with the DOW enzyme. The correlation between the toxicological and biochemical studies provides strong evidence that target-site insensitivity is an important mechanism of resistance to methomyl. The lack of significant cross-resistance to chlorpyrifos suggests that the insensitive AChE in these field populations was selected by methomyl alone and not by the organophosphate.     

Trans-ovum transmission of a cytoplasmic polyhedrosis virus of Heliothis virescens (Lepidoptera: Noctuidae)

Adults of Heliothis virescens infected with a cytoplasmic polyhedrosis virus (CPV) produced healthy offspring when their eggs were surface sterilized with either 15% formaldehyde or 0.2% sodium hypochlorite solution. Larvae from infected parents (1) cultured on a vitamin-deficient medium, (2) exposed to cold treatment (5°C, 24 hr), or (3) as progeny of adults from diapaused infected pupae, produced the same number of infected individuals as larvae reared in the customary way. Field studies indicated that the percent of CPV infection in larvae originating from virus-infected parents was density dependent.     

Benzylideneacetone, an immunosuppressant, enhances virulence of Bacillus thuringiensis against beet armyworm (Lepidoptera: Noctuidae)

Benzylideneacetone (BZA) is a metabolite of gram-negative entomopathogenic bacterium Xenorhabdus nematophila, and it acts as an enzyme inhibitor against phospholipase A2 (PLA2). PLA2 catalyzes a committed biosynthetic step of eicosanoids, which mediate insect immune reactions to infection by microbial pathogens. This study tested a hypothesis that a putative immunosuppressive activity of BZA may enhance virulence of Bacillus thuringiensis against the fifth instars of Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae). In in vitro conditions, BZA significantly inhibited hemocyte microaggregation induced by B. thuringiensis and impaired hemocyte-spreading behavior of S. exigua in a dose-dependent manner. Oral administration of BZA gave similar immunosuppressive effect on the hemocytes of the fifth instars. Although BZA itself did not possess any insecticidal activity on oral administration, when BZA was treated in a mixture with a low dose of B. thuringiensis spp. aizawai to fifth instars, the bacterial virulence was significantly enhanced. BZA also enhanced virulence of B. thuringiensis spp. kurstaki, which alone was of limited effectiveness against S. exigua. This study suggests that an immunosuppression by BZA is positively linked to potentiation of B. thuringiensis.     

Dissolution of Autographa californica nuclear polyhedrosis virus polyhedra by the digestive fluid of Trichoplusia ni (Lepidoptera:Noctuidae) larvae

The dissolution of polyhedra of Autographa californica nuclear polyhedrosis virus by digestive fluid collected from 5th stage Trichoplusia ni larvae was studied in vitro. Observations were made at timed intervals using phase contrast microscopy, and scanning and transmission electron microscopy. Dissolution occurred rapidly and in a detectable sequence. Under phase contrast, most polyhedra lost their refringence by 0.5 min. The polyhedra became rounded in appearance with small protuberances on the surface and Brownian movement was observed within. After 1 min, the envelope of most polyhedra had ruptured, releasing the enclosed virions. The protuberances were also observed under the scanning electron microscope after digestion for 0.5 min. Many shell fragments devoid of internal contents were seen after more lengthy digestion. Internal structural changes were revealed by electron microscopy. After 1 min of exposure, polyhedra were observed in all stages of dissolution. By 3 min, only virions, scattered about in heterogeneous material, could be distinguished.     

Characterization of fall armyworm mitochondrial DNA (Lepidoptera: Noctuidae)

Mitochondrial DNA from the fall armyworm, Spodoptera frugiperda (J.E. Smith), was cloned and characterized using restriction enzyme mapping. Genome size is approximately 16.3 kilobase (Kb), consistent with that of most animals. Three fragments, 8.1 Kb, 6.2 Kb, and 2.0 Kb, were produced by digestion with restriction enzyme Xbal and cloned into a pUC19 vector. Twenty-nine restriction enzymes were used to generate a detailed physical restriction enzyme map of the three cloned fragments. These data represent the first detailed characterization of a lepidopteran mitochondrial genome. © 1992 Wiley-Liss, Inc.     

Analysis of deoxyribonucleic acid from five nuclear polyhedrosis viruses infecting plusiine larvae (Lepidoptera: Noctuidae)

Deoxyribonucleic acid (DNA) from isolates of five nuclear polyhedrosis viruses (NPV) from lepidopterous hosts of the noctuid subfamily Plusiinae was analyzed by ion-exchange and paper chromatography. Viruses and production hosts were: Trichoplusia ni singly embedded virion type (SEV) from T. ni, Pseudoplusia includens SEV from P. includens, T. ni multiply embedded virion type (MEV) from T. ni, Autographa californica MEV from A. californica, A. californica MEV from T. ni, and Rachiplusia ou MEV from R. ou. Neither uracil nor 5-methyl cytosine was detected in the DNAs. Adenine:thymine (A:T) and guanine:cytosine (G:C) ratios were nearly constant for all the NPVs. AT:GC ratios for the SEVs were 1.60 and 1.57 and were clearly separable from those of the MEVs which ranged from 1.32 to 1.38. No differences in DNA composition within SEV or MEV groups were apparent.