Navel Orangeworm Research Articles

Total effects of contact and residual exposure of bifenthrin and λ-cyhalothrin on the predatory mite Galendromus occidentalis (Acari: Phytoseiidae)

Pyrethroid insecticides are generally regarded as acutely toxic to predatory phytoseiid mites; however, persistence of hull split spray pyrethroid residues on almond trees and their effects on phytoseiids have not been quantified over time. Hull split, the separation of the almond hull along the suture, exposes the new crop nuts to infestation by Amyelois transitella (Walker) larvae, and is the preferred timing for insecticides applied for their control. Galendromus occidentalis (Nesbitt) is the most important phytoseiid biocontrol agent for web-spinning spider mites in California (USA) almond orchards, and the impact of bifenthrin and λ-cyhalothrin pyrethroid residue on their survival, fertility, and fecundity was determined. The total effects of direct contact with esfenvalerate, permethrin, bifenthrin and λ-cyhalothrin were also evaluated for comparison. The total effects (E) of direct contact treatments of the four pyrethroids ranged from 77.8 % for esfenvalerate to 98.8 % for bifenthrin. Both bifenthrin and λ-cyhalothrin twig residue would be considered harmful (IOBC class 4) following field application at hull split timing. Bifenthrin twig residue would be considered slightly harmful (IOBC class 2) for up to 3.5 months and harmless (IOBC class 1) after 6 months. λ-cyhalothrin residue would be considered moderately harmful (IOBC class 3) for up to 3.5 months following application and harmless (IOBC class 1) after 6 months. Bifenthrin and λ-cyhalothrin twig residue on treated trees significantly reduced G. occidentalis female survival for up to 6 months post-treatment, however total effects (E) classify these residues as harmless (IOBC class 1) after 6 months. Harmful effects of direct and residual exposure following application have implications for the use of these pyrethroids in an integrated mite management program for perennial crops.

Crystallographic Observation of pH-Induced Conformational Changes in the Amyelois transitella Pheromone-Binding Protein AtraPBP1

The navel orangeworm, Amyelois transitella is a major agricultural pest causing large losses in a variety of tree crops. Control of this insect pest may be achieved by interfering with olfactory pathways to block detection of female-produced sex pheromones and consequently, disrupt mating. The first component of this pathway is the pheromone-binding protein AtraPBP1, which recognizes the pheromone and presents it to the odorant receptor housed in a sensory neuron of the male antennae. Release of the ligand depends on a pH-induced conformational change associated with the acidity of the membrane surface. To characterize this conformational change and to understand how pheromones bind, we have determined the high resolution crystal structures of AtraPBP1 in complex with two main constituents of the sex pheromone, i.e., (11Z,13Z)-hexadecadienal and (11Z,13Z)-hexadecadienol. Comparison with the structure of the unliganded form demonstrates a large ∼90° movement of the C-terminal helix which is observed in other pheromone- or odorant-binding proteins accompanied by an unpredicted 37° displacement of the N-terminal helix. Molecular dynamic trajectories suggest that the conformational change of the α1 helix facilitates the movement of the C-terminal helix.

Effect of Abundance of the Navel Orangeworm on Sampling Range and Interference Between Pheromone Traps

The sampling range of pheromone traps for the navel orangeworm Amyelois transitella (Walker) (Lepidoptera: Pyralidae) and its association with abundance was investigated by examining mutual interference within cross-shaped arrays of nine wing traps baited with virgin females and placed at 400-m intervals in three 256-ha blocks of almonds (Prunus dulcis [Miller] D. A. Webb), and three of pistachios (Pistacia vera L.). The proportions of males captured in the different positions were compared with the mean males for all traps, used as an index for abundance. For means between zero and 50 males per trap per week, the distribution was unequal between trap positions and the greatest proportion of males were captured in the northern-most trap (i.e., the within-row direction). Between 50 and 100 males per trap per week, most males were captured in the western-most traps and fewest in the center, and proportions were equal in other trap positions. Above 100 males per trap per week, the proportion of males captured was more nearly equal for all trap positions. These results demonstrate that the sampling range of pheromone traps for navel orangeworm is density dependent and, at low densities, is >400 m. They also indicate that abundance affects the impact of direction (orientation) of trap interference. At low density, female-strength pheromone traps sample males from beyond the block in which they are placed for orchard blocks of <50 ha.

Correction to Hull Split and Damaged Almond Volatiles Attract Male and Female Navel Orangeworm Moths

Correction to Hull Split and Damaged Almond Volatiles Attract Male and Female Navel Orangeworm Moths

Field Efficacy and Application Timing of Methoxyfenozide, a Reduced-Risk Treatment for Control of Navel Orangeworm (Lepidoptera: Pyralidae) in Almond

Large-scale field efficacy trials of methoxyfenozide (Intrepid), a reduced-risk molting agonist insecticide, were conducted in 2004 and 2005 in an orchard containing 'Nonpareil' and 'Sonora almonds [Prunus dulcis (Mill.) D.A. Webb] located in Kern County, CA. Methoxyfenozide applied one to three times, the organophosphate phosmet (Imidan) alone or in combination with methoxyfenozide, or the pyrethroid permethrin (Perm-Up) were tested for efficacy against the primary lepidopteran pest navel orangeworm, Amyelois transitella (Walker) (Lepidoptera: Pyralidae), and three other lepidopteran pests of almond: oriental fruit moth, Grapholita molesta (Busck); oblique-banded leafroller, Choristoneura rosaceana (Harris); and peach twig borer, Anarsia lineatella Zeller. Two or three applications of methoxyfenozide (bracketing hull split or spring plus bracketing hull split) were more effective than a single hull split application of phosmet, phosmet combined with permethrin, or methoxyfenozide. In these trials, a spring application followed by a posthull split application was as effective as the applications bracketing hull split. Navel orangeworm accounted for > 60% of the total damage, whereas oriental fruit moth and peach twig borer were the dominant secondary pests. In experiments conducted in 2010 to assess the direct toxicity of methoxyfenozide to navel orangeworm eggs under field conditions, exposure to methoxyfenozide reduced survival by 96-99%. We conclude that this reduced-risk insecticide is effective, although its efficacy is maximized with more than one well-timed application.

미국산 오렌지 생과실에서 검출된 Navel Orangeworm (나비목: 명나방과)

2012년 1월 31일 농림수산검역검사본부 영남지역본부 부산신항사무소에서 미국산 오렌지 생과실 화물을 검사하는 과정에서 Navel orangeworm, Amyelois transitella (Walker)이 검출되었다. 이 해충의 유충이 간혹 호두 과실 속에서 검출된 예가 알려져 있지만, 오렌지 생과실 속에서 검출된 경우는 처음이다. 여기서는 식물검역의 안전성을 보장할 목적으로 이 유충의 진단형질 및 미국산 오렌지 생과실에 대한 병해충수입 위험분석과 관련된 검출정보를 제공하고자 한다. Navel orangeworm, Amyelois transitella (Walker) was intercepted at the Korean port of entry. It was detected by an inspection for a consignment of fresh oranges from the USA by the Busan Newport District Office, Yeongnam regional office, Animal Plant and Fisheries Quarantine and Inspection Agency on January 31, 2012. This is the first time that the larvae of this pest species has been detected on fresh oranges, although it has been occasionally detected on walnuts. This report aims to ensure biosecurity by providing diagnostic characters to identify the caterpillars and conducting an imported risk analysis on fresh oranges from the USA.

Hull Split and Damaged Almond Volatiles Attract Male and Female Navel Orangeworm Moths

A blend of volatiles derived from the emissions of almonds at hull split and mechanically damaged almonds was compared to almond meal, the current monitoring standard for the insect pest navel orangeworm (NOW). Field trapping studies were performed to determine the blend's ability to attract adult NOW. The blend comprised racemic 1-octen-3-ol, ethyl benzoate, methyl salicylate, acetophenone, and racemic (E)-conophthorin. Ethyl acetate was used as a solvent with a blend component concentration of 100 mg/mL. The blend attracted both sexes of NOW when tested in five 2-week intervals spanning the first three flights of NOW in commercial almond orchards in the southern Central Valley of California. The blend demonstrated consistently higher capture rates for female NOW throughout the evaluation period, but unlike almond meal it significantly attracted males. Reported is a survey of the major and minor volatiles emitted from almonds at hull split, the key period of vulnerability to NOW infestation. Also reported is the attractancy of a formulated test blend based on the host plant volatile emissions, electroantennographic screening experiments, and field trapping studies. The results of this test blend highlight progress toward a host-plant-based attractant for NOW, a major insect pest of California tree nuts that presently lacks an adequate monitoring tool.

Evaluation of Monitoring Traps with Novel Bait for Navel Orangeworm (Lepidoptera: Pyralidae) in California Almond and Pistachio Orchards

Experiments conducted in three almond, Prunus dulcis (Rosales: Rosaceae), orchards and three pistachio, Pistacia vera (Sapindales: Anicardiaceae), orchards in 2009 and 2010, and determined that sticky bottom wing traps baited with ground pistachio mummies, or a combination of ground pistachio plus ground almond mummies, trapped more adult female navel orangeworm, Amyelois transitella (Walker) (Lepidoptera: Pyralidae), than did traps baited with ground almond mummies alone. During both years of this study, 2.9 and 1.8 more moths were caught in traps baited with pistachio mummies compared with traps baited with almond mummies in almond orchards and pistachio orchards, respectively. Also, traps located in pistachio orchards caught 5.9 and 8.3 times more navel orangeworm than were trapped from almond orchards in 2009 and 2010, respectively. Implications for use of this novel baited trap in almond and pistachio orchard integrated pest management programs are discussed.

Radio frequency disinfestation treatments for dried fruit: Dielectric properties

Phytosanitary/quarantine regulations for many countries require that certain dried fruit be disinfected prior to export; however, current technologies involve the use of toxic chemicals and conventional thermal methods are either undesirable or cause loss of volatile components, browning and texture change. Newer physical methods including dielectric heating have been considered, but information on dielectric properties of dried fruits is lacking. Because the loss factor of insect pests, Indian meal moth (Plodia interpunctella) and navel orangeworm (Amyelois transitella), is several times (26–36) greater than that of dried fruits, RF treatment in particular has great potential for insect disinfection. In this study, the dielectric properties of raisins, dates, apricots, figs, and prunes with water contents of 15–30.2g/100g, were determined between 10 and 1800MHz over a range of 20–60°C. The dielectric constant and loss factor of all samples decreased with increasing frequency, but increased with increasing temperature at each frequency. The loss factor of all samples increased with increasing water contents/water activity (0.5–0.7). The penetration depths (dps) of RF energy in all samples decreased with increasing frequency and temperature. The deep dp (28.4–103.7cm) at 27MHz indicates the potential for developing continuous and large-scale RF treatments for postharvest insect control in dried fruits.

Moth Sex Pheromone Receptors and Deceitful Parapheromones

The insect's olfactory system is so selective that male moths, for example, can discriminate female-produced sex pheromones from compounds with minimal structural modifications. Yet, there is an exception for this “lock-and-key” tight selectivity. Formate analogs can be used as replacement for less chemically stable, long-chain aldehyde pheromones, because male moths respond physiologically and behaviorally to these parapheromones. However, it remained hitherto unknown how formate analogs interact with aldehyde-sensitive odorant receptors (ORs). Neuronal responses to semiochemicals were investigated with single sensillum recordings. Odorant receptors (ORs) were cloned using degenerate primers, and tested with the Xenopus oocyte expression system. Quality, relative quantity, and purity of samples were evaluated by gas chromatography and gas chromatography-mass spectrometry. We identified olfactory receptor neurons (ORNs) housed in trichoid sensilla on the antennae of male navel orangeworm that responded equally to the main constituent of the sex pheromone, (11Z,13Z)-hexadecadienal (Z11Z13-16Ald), and its formate analog, (9Z,11Z)-tetradecen-1-yl formate (Z9Z11-14OFor). We cloned an odorant receptor co-receptor (Orco) and aldehyde-sensitive ORs from the navel orangeworm, one of which (AtraOR1) was expressed specifically in male antennae. AtraOR1•AtraOrco-expressing oocytes responded mainly to Z11Z13-16Ald, with moderate sensitivity to another component of the sex pheromone, (11Z,13Z)-hexadecadien-1-ol. Surprisingly, this receptor was more sensitive to the related formate than to the natural sex pheromone. A pheromone receptor from Heliothis virescens, HR13 ( = HvirOR13) showed a similar profile, with stronger responses elicited by a formate analog than to the natural sex pheromone, (11Z)-hexadecenal thus suggesting this might be a common feature of moth pheromone receptors.

Electroantennographic Bioassay as a Screening Tool for Host Plant Volatiles

Plant volatiles play an important role in plant-insect interactions. Herbivorous insects use plant volatiles, known as kairomones, to locate their host plant. When a host plant is an important agronomic commodity feeding damage by insect pests can inflict serious economic losses to growers. Accordingly, kairomones can be used as attractants to lure or confuse these insects and, thus, offer an environmentally friendly alternative to pesticides for insect control. Unfortunately, plants can emit a vast number volatiles with varying compositions and ratios of emissions dependent upon the phenology of the commodity or the time of day. This makes identification of biologically active components or blends of volatile components an arduous process. To help identify the bioactive components of host plant volatile emissions we employ the laboratory-based screening bioassay electroantennography (EAG). EAG is an effective tool to evaluate and record electrophysiologically the olfactory responses of an insect via their antennal receptors. The EAG screening process can help reduce the number of volatiles tested to identify promising bioactive components. However, EAG bioassays only provide information about activation of receptors. It does not provide information about the type of insect behavior the compound elicits; which could be as an attractant, repellent or other type of behavioral response. Volatiles eliciting a significant response by EAG, relative to an appropriate positive control, are typically taken on to further testing of behavioral responses of the insect pest. The experimental design presented will detail the methodology employed to screen almond-based host plant volatiles by measurement of the electrophysiological antennal responses of an adult insect pest navel orangeworm (Amyelois transitella) to single components and simple blends of components via EAG bioassay. The method utilizes two excised antennae placed across a "fork" electrode holder. The protocol demonstrated here presents a rapid, high-throughput standardized method for screening volatiles. Each volatile is at a set, constant amount as to standardize the stimulus level and thus allow antennal responses to be indicative of the relative chemoreceptivity. The negative control helps eliminate the electrophysiological response to both residual solvent and mechanical force of the puff. The positive control (in this instance acetophenone) is a single compound that has elicited a consistent response from male and female navel orangeworm (NOW) moth. An additional semiochemical standard that provides consistent response and is used for bioassay studies with the male NOW moth is (Z,Z)-11,13-hexdecadienal, an aldehyde component from the female-produced sex pheromone.

Effects of a Naturally Occurring and a Synthetic Synergist on Toxicity of Three Insecticides and a Phytochemical to Navel Orangeworm (Lepidoptera: Pyralidae)

The navel orangeworm, Amyelois transitella (Walker) (Lepidoptera: Pyralidae), is the most destructive lepidopteran pest of almonds [Prunus dulcis (Mill.) D.A.Webb] and pistachios (Pistacia vera L.) in California and is a serious problem in figs (Ficus carica L.) and walnuts (Juglans spp.). In addition to direct damage, larval feeding leaves nuts vulnerable to infection by Aspergillus spp., fungi that produce toxic aflatoxins. A potentially safe and sustainable approach for managing navel orangeworm in orchards may be to use natural essential oil synergists to interfere with this insect's ability to detoxify insecticides and phytochemicals. We tested the effects of a naturally occurring plant-derived chemical, myristicin, and a synthetic inhibitor of cytochrome P450 monooxygenases (P450s), piperonyl butoxide, on the toxicity of three insecticides (alpha-cypermethrin, tau-fluvalinate, and methoxyfenozide [Intrepid]) and a phytochemical (xanthotoxin) to A. transitella. Piperonyl butoxide significantly synergized alpha-cypermethrin and tau-fluvalinate, whereas myristicin synergized only alpha-cypermethrin. Piperonyl butoxide synergized the toxicity of xanthotoxin as early as 72 h after exposure, whereas myristicin synergized xanthotoxin after 120 h. In view of these findings and the limited availability of environmentally safe synthetic insecticides for sustainable management, particularly in organic orchards, myristicin is a potential field treatment in combination with insecticides to reduce both navel orangeworm survival and aflatoxin contamination of nuts. In addition, this study demonstrates that in A. transitella the insect growth regulator methoxyfenozide is not detoxified by P450s.

Ecological influence of the entomopathogenic nematode, Steinernema carpocapsae, on pistachio orchard soil arthropods

Abstract The entomopathogenic nematode, Steinernema carpocapsae, can reduce pesticide reliance in pistachios by controlling overwintering larvae of the navel orangeworm, Amyelois transitella (Lepidoptera: Pyralidae). But, beyond this, their influence in pistachio soil food webs is unclear. Given soil food webs’ complexity, S. carpocapsae likely interact with more species than just their intended target, infecting alternate hosts or providing food for native predators. This study quantifies the nematodes’ effects on soil arthropod and surface arthropod diversity in two large orchards in Madera County, California. We found significantly more isotomid collembolans, predatory anystid mites and gnaphosid spiders under trees where nematodes were applied indicating either direct predation or indirect trophic effects. Significantly fewer Forficula auricularia (Dermaptera: Forficulidae) and Blapstinus discolor (Coleoptera: Tenebrionidae) were found under treated trees, suggesting a possible non-target infection. Nematode persistence was limited but positively correlated with pitfall catches of the tenebrionid beetles, Nyctoporis cristata and B. discolor.

Molecular cloning and characterization of sensory neuron membrane protein and expression pattern analysis in the diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae)

Olfactory proteins in insects are extremely diverse. The sensory neuron membrane protein (SNMP) olfactory receptor, which shares a high identity among different insects, has been shown to be essential for olfaction perception in insects. To research the function of SNMP, the gene encoding SNMP from Plutella xylostella Linnaeus (Lepidoptera: Plutellidae) was cloned and named PxyloSNMP1 (GenBank accession no. HM536984). The sequencing results showed that the open reading frame of PxyloSNMP1 had the characteristics of SNMP, with two putative transmembrane domains flanking a large extracellular loop and a 34-residue hydrophobic signal peptide sequence. The amino acid sequence of PxyloSNMP1 had a high degree of similarity with those from other insect species and shared 78.8% identity with the SNMP sequence from Amyelois transitella Walker (Lepidoptera: Pyralidae). RT-PCR analysis revealed that the gene was expressed during all life-history stages and in all adult tissues. Quantitative real-time PCR (qPCR) analysis also showed that the PxyloSNMP1 transcript could be observed in different developmental stages at different levels of expression. The tissue expression pattern further indicated that PxyloSNMP1 was expressed most in the antenna of P. xylostella, followed by the abdomen, head (without antenna), wing, leg and thorax. This study provides a basis for further studies of the function of SNMP from P. xylostella.

Microencapsulated Pear Ester Enhances Insecticide Efficacy in Walnuts for Codling Moth (Lepidoptera: Tortricidae) and Navel Orangeworm (Lepidoptera: Pyralidae)

The efficacy of combining insecticides with a microencapsulated formulation of ethyl (2E,4Z) -2,4-decadienoate (pear ester, PE-MEC) was evaluated in walnuts, Juglans regia L., for codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae), and navel orangeworm, Amyelois transitella Walker (Lepidoptera, Pyralidae). Two types of studies were conducted to compare the use of insecticides with and without PE-MEC. In the first study, PE-MEC in combination with reduced rates of insecticides, including chlorpyrifos, phosmet, methoxyfenozide, and codling moth granulovirus were evaluated in single tree replicates. PE-MEC was tested at one to three rates (0.6, 1.8, and 4.4 g active ingredient ha(-1)) with each insecticide. In the second study, seasonal programs including sprays of esfenvalerate, chlorpyrifos, and ethyl parathion at full rates were evaluated in replicated two ha blocks. Significant reductions in nut injury occurred in the single-tree trial with treatments of PE-MEC plus insecticide compared with the insecticides used alone against both pest species; except with methoxyfenozide for navel orangeworm. Similarly, nut injury in the large plots was significantly reduced with the addition of PE-MEC, except for navel orangeworm in one of the two studies. These results suggest that adding pear ester as a microencapsulated spray can improve the efficacy of a range of insecticides for two key pests and foster the development of integrated pest management tactics with reduced insecticide use in walnut.

Hull Split Date and Shell Seal in Relation to Navel Orangeworm (Lepidoptera: Pyralidae) Infestation of Almonds

Hull split date, shell seal, and navel orangeworm, Amyelois transitella (Walker) (Lepidoptera: Pyralidae), infestation data for 19 varieties of almonds, Prunus dulcis (Mill.) D.A. Webb, were analyzed to determine the relationship of shell seal and hull split date on A. transitella infestation. Data for all varieties were collected from three University of California regional almond variety trials from 2003 to 2005, with a total of 8,550 nuts evaluated. A significant negative relationship was found between percentage of shell seal and percentage of navel orangeworm infestation, with lower percentage of shell seal correlating to higher percentage of infestation. Similarly, hull split date was negatively correlated with percentage of infestation, with later splitting varieties trending toward lower percentage of infestation. Although there are outlying varieties, hull split and shell seal are indeed significant components in varietal differences in almond navel orangeworm infestation. Understanding such factors gives insight into both the predictive value of almond characteristics related to navel orangeworm damage as well as other potential indicators.

Comparison of Trapping for Eggs, Females, and Males of the Naval Orangeworm (Lepidoptera: Pyralidae) in Almonds

The navel orangeworm is the primary insect pest of almonds in California, and egg traps are the primary means of monitoring this pest. A previous study found that the current use of 2-4 traps per 64 ha block usually is not sufficient to provide management information specifically for that block. In this study, we compare data from large grids of egg traps in varied commercial almond orchards with trapping data for females and males, with the objective of finding a more cost-effective monitoring program using currently available attractants. The proportion of egg traps with eggs was highly correlated with mean eggs per egg trap, and with females and males trapped simultaneously at the same location. Almond variety and the type of bait used had little impact on the relationship between the proportion of egg traps with eggs and the number of eggs per traps. Traps in orchards with more unharvested (mummy) almonds had more eggs, suggesting that navel orangeworm abundance affected traps more than competition from mummies. Laboratory experiments comparing age-specific oviposition in two-choice and no-choice situations found that younger, more fecund females laid a greater proportion of eggs on the preferred substrate in a two-choice situation, but that age-specific fecundity was not different between substrates in no-choice tests. These findings indicate that the proportion of egg traps with eggs provides a more stable indication of navel orangeworm phenology than mean eggs per trap. We suggest that similar information could be obtained in a more cost-effective manner with female trapping.

Ambient orchard volatiles from California almonds

The volatile emissions of various plant parts of almonds have been studied via various techniques in the past. These analyses have typically been performed on single cultivars and hence may not be representative of the volatiles found in an entire almond orchard. Recent reports suggest some almond volatiles exhibit semiochemical activities for the navel orangeworm (NOW), a major insect pest of almonds; thus, the volatile composition of the comprehensive almond orchard would be helpful to research concerning NOW. The ambient volatile emissions of an almond orchard containing the cultivar Nonpareil and associated pollenizers were collected at four intervals during the 2009 growing season from orchards in the south Central Valley of California. The volatiles hexanal, octanal, nonanal, benzaldehyde, acetophenone, ethyl benzoate, methyl salicylate, and phenol were consistent in their presence and in relatively high amounts. The orchard volatile composition was analyzed via electroantennogram (EAG) analysis, which produced strong responses from NOW antennae.

Effect of Natural and Artificial Photoperiods and Fluctuating Temperature on Age of First Mating and Mating Frequency in the Navel Orangeworm,Amyelois transitella

The effect of weak illumination during part or all of the scotophase on mating frequency of navel orangeworm, Amyelois transitella (Walker) (Lepidoptera: Pyralidae), was examined in environmental chambers under long photoperiods and constant warm temperature (colony conditions) or shorter photoperiods and a cooler thermoperiod intended to mimic spring conditions in our region. These data were compared to mating frequencies in sentinel females placed in the field during the first three weeks of May. Under colony conditions weak illumination in the final hour of the scotophase resulted in ∼90% mating on the first day after eclosion; significantly greater mating compared to complete darkness throughout the scotophase, weak illumination throughout the scotophase, or weak illumination for both the first and last hour of the scotophase. In an environmental chamber programmed to simulate spring conditions, little mating occurred on the first night after eclosion and three nights were required for more than 50% of the females to mate. There was no difference in mating frequency with between moths exposed to complete darkness throughout the scotophase and those provided with weak illumination in the last half hour of the scotophase or throughout the scotophase. This delay in age of first mating was consistent with field observations with sentinel females at May in the central San Joaquin Valley. The authors conclude that, along with greater longevity and later oviposition, first mating occurs at a later age in spring conditions compared to summer conditions in this species. Planned studies of the effect of delayed mating in first and second flights will need to take these factors into account.

Variable Developmental Rate and Survival of Navel Orangeworm (Lepidoptera: Pyralidae) on Pistachio

A series of laboratory and field studies were conducted using two lines of navel orangeworm, reared on different stages of new crop and mummy pistachios, Pistacia vera L. This study demonstrated the potential importance of malformed pistachios (pea splits) to the population dynamics of navel orangeworm, because these nuts, which are available as early as two months before mature nuts, supported navel orangeworm development and survival. Overall, the developmental rate on new crop pistachios is fastest on mature nuts, 422.3 +/- 123 degree-days (DD, degrees C), but other factors such as exposure to insecticide residue also sped development, although survival decreased. Development took the longest on unharvested nuts (mummies) dried at 90 degrees C for 24 h, 2664.7 +/- 131.4 DD. In most trials development was variable and two generations could develop at the fastest rate before the slowest individual completed development, which in turn calls into question the concept of discrete generations. Generally, survival was highest on mature pistachios and other stages of new crop nut and lowest on mummies collected in May. Survival was also higher on the new varieties 'Lost Hills' and 'Golden Hills' (24.7 and 32.0%, respectively) than on the most extensively planted variety 'Kerman' (13.3%). In our trials, both the rate of development and survival were dependent on nut stage, age, variety, and quality, indicating that pistachios, like almonds, Prunus dulcis (Mill.) D. A. Webb, are a dynamic rather than a static nutrient source for navel orangeworm.