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.     

Comparison of the volatile emission profiles of ground almond and pistachio mummies: Part 1 – Addressing a gap in knowledge of current attractants for navel orangeworm

Over the years various tissues of almond and pistachio have been evaluated for their ability to attract the navel orangeworm moth, a major insect pest in California tree nut orchards. Almond meal, which typically consists of ground almond kernels, is a monitoring tool for navel orangeworm populations in almond and pistachio orchards. Recently, ground pistachio and almond mummies have been re-visited in field trapping studies for their potential to attract navel orangeworm moths. Surprisingly, the volatile profiles of these two systems have not been reported. The objective of this study was to survey and then compare and contrast the volatile profiles of both ground almond and pistachio mummies over the course of a week. Principal component analysis (PCA) of the headspace volatiles showed a distinct difference between ground almond and pistachio mummies. The volatile emission profile of the almond mummies remained consistent over the one-week period, albeit in low content and composition; whereas the profile of the pistachio mummies changed over time as shown by PCA. Seven compounds were identified as being common volatiles to both matrices. These data may help explain results from recent navel orangeworm field trapping studies using almond and pistachio mummies, as well as with the formulation of future synthetic blends.     

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.     

Effect of bait formulation and number of traps on detection of navel orangeworm (Lepidoptera: Pyralidae) oviposition using egg traps

Egg traps are the primary tool for monitoring egg deposition of the navel orangeworm, Amyelois transitella (Walker) (Lepidoptera: Pyralidae), and for timing treatments for this pest in almonds, Prunus amygdalus Batsch, and pistachios, Pistacia vera L. We compared, in almond and pistachio orchards, the number of eggs per trap in traps baited with almond meal, pistachio meal, or the current standard commercial bait. When considering cumulative eggs captured over an extended period, traps baited with pistachio meal prepared from previous-crop nuts generally captured a similar number of eggs compared with the commercial bait, and more eggs than those baited with almond meal prepared from previous-crop nuts. However, differences in eggs per trap between bait formulations were not as evident when examining individual weeks, particularly in weeks with few eggs per trap, as is typical when treatment decisions are made. The variance in eggs per trap was generally greater than the mean and increased with the mean and, when mean eggs per trap was low, most traps did not have eggs. We discuss implications of these findings for the relative importance of bait type and trap numbers for monitoring, and for experiments comparing egg trap performance.     

Effects of mating disruption treatments on navel orangeworm (Lepidoptera: Pyralidae) sexual communication and damage in almonds and pistachios

Two experiments in 2003 examined the effects of different ways of dispensing the principal sex pheromone component on sexual communication among and crop damage by the navel orangeworm, Amyelois transitella (Walker) (Lepidoptera: Pyralidae) in Nonpareil almonds and pistachios. A third experiment in 2004 compared the effect on navel orangeworm damage to several almond varieties using one of these dispensing systems by itself or with phosmet, phosmet alone, and an untreated control. Additional data are presented estimating release rates from timed aerosol release devices (PuffersNOW, Suterra LLC, Bend, OR) and hand-applied membrane dispensers. In 2003, puffers placed peripherally around 16-ha blocks, evenly spaced Puffers, and hand-applied dispensers reduced males captured in virgin-baited traps by > or = 95% and mating in sentinel females by > or = 69%, with evenly placed Puffers showing greater reduction of males captured and females mated compared with the other dispensing systems. Mating disruption with gridded Puffers or hand-applied devices in almonds resulted in an approximately 37% reduction of navel orangeworm damage (not significant), whereas peripheral Puffers resulted in a 16% reduction of navel orangeworm damage to almonds. In pistachios neither peripheral nor gridded Puffers reduced navel orangeworm damage, whereas insecticide reduced damage by 56%. In 2004, Puffers alone, insecticide alone, and both in combination significantly reduced navel orangeworm damage in Nonpareil almonds. In other, later harvested varieties, the insecticide treatments reduced damage, whereas the mating disruption treatment alone did not. We discuss application of these findings to management of navel orangeworm in these two crops.     

Ex situ volatile survey of ground almond and pistachio hulls for emission of spiroketals: Analysis of hull fatty acid composition,water content,and water activity

The spiroketal conophthorin has recently been implicated as an important semiochemical of the navel orangeworm moth (Amyelois transitella), a major insect pest to California tree nuts. Additionally, new evidence demonstrates that fungal spores in the presence of linoleic acid produce conophthorin. Numerous investigations have analyzed the volatile emissions of almonds and pistachios under varying conditions, yet there are few reports of conophthorin as a volatile component. Previous studies by our laboratories have suggested almond hulls may be a source of conophthorin production. Accordingly, the volatile emissions of ex situ almond and pistachio ground hulls were surveyed at several developmental stages. Each ground sample was analyzed at various intervals to determine if conophthorin was produced. The almond and pistachio samples were presumed to have a natural fungal bouquet present. Additionally, the fatty acid composition, water content, and water activity of the hulls were analyzed for each sample. Conophthorin and the structurally similar compound chalcogran were detected from almond hulls and shells, but not from the pistachio samples. The almond and pistachio hulls were investigated for four fatty acid components – palmitic, oleic, linoleic, and linolenic. The fatty acid composition of almond hulls varied greatly throughout the growing season, whereas the composition of pistachio hulls remained relatively constant. Both water content and activity were constant in early stages of almond growth then dropped in the later stages of hull split. Spiroketal emission along with other associated volatiles is discussed. This is the first report of the fatty acid composition, water content, and water activity of developing almond and pistachio hulls.     

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.     

Sexual behavior of the navel orangeworm, Amyelois transitella (Walker) (Lepidoptera: Pyralidae)

To get a better understanding of the mating behavior of the navel orangeworm, Amyelois transitella (Walker), we developed a robust laboratory colony derived from larvae collected in Bakersfield, California and fed on dried, roasted pistachio. In the lab at 25 degrees C, most of the mating activity was observed during the last hour of the scotophase and for the first 30 min of the photophase. Female calling was characterized by the abdomen being protruded between the wings with the distal segments perpendicular to the body and exposing a pheromone gland, as well as by continuous antennation. Males approached calling females from a short distance by displaying wing fanning and antennation. When a male antennated on a calling female's abdomen, she either accepted the male and lowered the abdomen, or walked away. The accepted male made a final approach parallel to the female's body, but after coupling he rotated 180 masculine with male and female remaining in a linear, abdomen-to-abdomen position for over 3 h in average. In a possible strategy to maximize the chances of mating, the sex ratio was significantly skewed towards males in the first two days of emergence. Almost 80% of mating took place in the first two days after adult emergence, with females mating only once. About 55% of males mated only once and approximately 40% of the observed males mated twice and 5% tree times.     

Seasonal biology and abundance of Psyllaephagus pistaciae,a biocontrol agent of the common pistachio psylla Agonoscena pistaciae

The solitary endoparasitoid Psyllaephagus pistaciae Ferrière (Hymenoptera: Encyrtidae), is the most widely distributed biological control agent of the common pistachio psyllid, Agonoscena pistaciae Burckhardt and Lauterer (Hemiptera: Psylloidea), in Iran. The pupation and overwintering sites of diapausing parasitoids and the psyllid were studied for 2 years using emergence traps in pistachio orchards in Rafsanjan, Iran. The psyllid mummies containing the overwintering parasitoid adhered to pistachio leaves and were carried on these leaves away from the tree when they latter senesced. The present results verified that plant litter which included dried grasses and old pistachio leaves tended to support a greater population of adult winter-form psyllid and psyllid mummies during the winter through early spring than other options examined. Adult parasitoids appeared in the field in early April, about 30 days after the emergence of adult psyllids, but almost at the same time as the hatching of the first generation psyllid nymphs in early April. Rates of parasitism of CPP were generally low throughout most of the year, ranging from 1 to 5%, but rose in late autumn to about 11%. Results suggest that the density of P. pistaciae is not great enough to keep pace with the psyllid populations in these orchards. They explain why growers consider it necessary to apply pesticides for this pest. However, this parasitoid undoubtedly does play an important role in the natural control of A. pistaciae late in the growing season, particularly in non-sprayed orchards. Conservation of these natural enemies should be one of the objectives in the development of sustainable pest management programs.     

Responses of production and storage walnut pests to Bacillus thuringiensis insecticidal crystal protein fragments

Recent advances in genetic engineering have provided the opportunity to induce walnut plants to produce Bacillus thuringiensis Berliner insecticidal crystal protein fragments (ICPFs) for insect control. We studied the effects of two ICPFs CryIA(b) and CrylA(c) previously shown to be encoded by the cryIA(b) and cryIA(c) genes in the B. thuringiensis strains HD-1 and HD-73, respectively. The lethal effects on larvae of codling moth, Cydia pomonella (L.), navel orangeworm, Amyelois transitella (Walker), and the major postharvest pest Indianmeal moth, Plodia interpunctella (Hübner), were investigated. Both proteins were toxic to the three species tested. Indianmeal moth larvae were the most susceptible and navel orangeworm the least; CryIA(b) was generally more toxic to navel orangeworm. Similar relationships resulted when ICPFs were incorporated into the diet. Both ICPFs caused decreased rate of development of navel orangeworm. Effects on pupal weight occurred only at the highest concentration (100 ng/cm²). Neither ICPF affected frequency of mating or fecundity. In addition to the lethal effects, the extended development times observed could have considerable effects on the population dynamics of the navel orangeworm and possibly other species.     

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.     

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.     

Age-specific survival and fecundity and their effects on the intrinsic rate of increase of Aphelinus gossypii (Hym., Aphelinidae), a parasitoid of Aphis gossypii (Hom., Aphididae)

Abstract: The age-specific survival and fecundity of female adults of the aphidophagous parasitoid, Aphelinus gossypii Timberlake (Hym., Aphelinidae), were determined at a host density of 50 Aphis gossypii Glover (Hom., Aphididae) per leaf of Ageratum houstonianum Mill each day at 25°C. The age-specific mummy production, emergence rate and sex ratio of progeny were calculated. The implication of these results in terms of potential population growth of A. gossypii and related species is discussed. The age-specific survival curve ( l _x ) of females exhibited a Type I pattern, which resulted in little difference between Σ m _x and Σ l _x   m _x . The l _x curve of males exhibited a Type II pattern, and their survival time was much shorter than that of females. Each mated female produced on average 598.9 ± 64.0 aphid mummies, and preyed on 87.9±6.2 aphids. Most of the biological performance parameters were not different significantly between mated and virgin females. The highly female-biased sex ratio of offspring produced by mated females soon after their emergence resulted in a high fecundity rate ( m _x ) during the early reproductive period. Therefore, although the sex ratio of progeny was male-biased during the entire reproductive period, the intrinsic rate of increase estimated using age-specific sex ratios was larger than that estimated using a constant sex ratio of 0.5. These results indicate that the high survival and the adaptation of producing mostly female offspring during the early reproductive period contribute much to the population increase potential of this parasitoid.     

Effect of male age structure on reproduction in white-tailed deer

Selective harvest regimes that create female-biased sex ratios can potentially lead to delayed breeding, reduced breeding synchrony, reduced productivity, and a female-biased sex ratio of offspring. These resulting changes in breeding behavior and population dynamics have potential to adversely affect population growth. In 2002, Pennsylvania implemented harvest regulation changes that reduced deer density (increased harvest of antlerless deer) and increased the number and age of antlered deer (implemented antler point restriction regulations) that resulted in a less female-biased sex ratio. We monitored date of conception, productivity (embryos/female), and sex ratio of embryos during 1999–2006 to test if timing of breeding occurred earlier and with greater synchrony, if productivity of females increased, and if the sex ratio of offspring would shift towards more males. Deer density decreased 23% and the adult (≥1.5 yr old) sex ratio declined from 2.30 to 1.95 females/male. The ratio of ≥2.5-year-old to 1.5-year-old males shifted towards more older males (1:3.7 in 2002 to 1:1.59 in 2006) and the ≥2.5-year-old male population increased from 41,853 during 1999–2001 to 54,064 by 2006. We found no evidence of any change in the timing or variability of date of conception, productivity, or offspring sex ratio. We conclude that harvest regulation changes implemented in Pennsylvania, USA, were insufficient to affect timing of breeding or population dynamics and that efforts by managers to identify a desired sex ratio or manipulate sex ratios to achieve management goals on a statewide scale will be challenging. © 2019 The Wildlife Society.     

Laboratory studies of Blattisocius keegani (Fox) (Acari: Ascidae) reared on eggs of navel orangeworm: potential for biological control

Blattisocius keegani (Fox) is a predatory mite in the family Ascidae (Acari), noted for potential biological control of Coleopteran stored product pests. Performance of B. keegani on eggs of navel orangeworm, Amyelois transitella Walker (Lepidoptera: Pyralidae), was investigated. Mites completed development from egg to adult in 9.2±0.22 days at 25°C and 50-60% relative humidity, and in 6.33±0.29 days at 32.2°C, 30% relative humidity. Mites provisioned with three or five eggs consumed a median of 1.25 to 1.5 eggs, with a maximum of three eggs consumed over 24?h. Regression analyses indicated egg-laying by B. keegani was significantly correlated with the number of A. transitella eggs consumed, and female mites laid an average of 5.82±0.44 eggs over 72?h. Blattisocius keegani, developed on fresh and frozen eggs, laid significantly more eggs when provided with fresh eggs (F3,26=6.16, P=0.0026) and were able to develop on frozen Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) eggs as an alternative host. Mites were equally fecund when fed eggs stored at 0° or -20°C. Provisioning of adult moth bodies in addition to egg prey items increased mite fecundity, although it was demonstrated that B. keegani are phoretic on adult moths as well. The results are the first experimental evidence of B. keegani as a predator of Lepidopteran eggs, as a phoretic species, and of their potential for biological control of navel orangeworm.     

Reproductive strategies of Diaeretiella rapae (Hymenoptera: Aphidiinae) during fluctuating temperatures of spring season in New Zealand

Reproductive activities of naturally occurring population of Diaeretiella rapae (M'Intosh) (Hymenoptera: Aphidiinae) on Myzus persicae were studied during spring season in New Zealand. The cabbage seedlings were highly infested with the aphids (272±25 individuals/plant) with about 30% on average parasitised by D. rapae. Rate of parasitism was positively correlated with the aphid density (R ²=0.64). Adult emergence from aphid mummies was 90%, with a higher frequency of females than males. Increase in female/male sex ratio was found between early and late spring (1.1 vs. 1.8). Mating in D. rapae occurred throughout the day. Nearly half of the mating pairs collected were male–male pairs, which were especially prevalent during morning and evening while more male–female mating pairs were found during midday. Male–male mounting was probably because of low number of virgin females in morning and evening populations. About 80% females were mounted by smaller size males. Male–male mounting is discussed in correlation with operational sex ratio of D. rapae population.     

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.     

Substantial progress made in the rearing of the European cherry fruit fly, Rhagoletis cerasi

We examined phenyl propionate as an attractant for trapping navel orangeworm, Amyelois transitella (Walker) (Lepidoptera: Pyralidae) adults, with the objective of developing a method of trapping both sexes more effectively than with almond meal. Two initial experiments maximized the total number of adults captured using phenyl propionate released from glass vials with cotton wicks. A third experiment compared the numbers of males and females captured using these glass dispensers in either bucket or sticky traps. The glass vial dispensers captured more adults than 0.1% phenyl propionate in water (as both attractant and killing agent), and far more adults were captured with glass vial phenyl propionate dispensers than with almond meal. On rare occasion, the glass vial dispensers captured as many adults as traps baited with virgin females, but usually phenyl propionate in glass vials captured fewer adults than virgin‐baited traps. Glass vial phenyl propionate dispensers were equally effective in sticky traps or bucket traps. The majority of females captured were mated, and the proportion of males captured increased over time within flights (generations). We conclude that phenyl propionate released from glass vials captured A. transitella adults more effectively than currently available options, and will be useful in research projects where capturing intact adults and comparing mating status are important. Developing a cost‐effective phenyl propionate‐based alternative to the egg traps currently used for commercial monitoring will be more difficult.     

花尾榛鸡的非对称性比和成体存活率

1999至2002年,在法国东南部的阿尔卑斯山,通过无线电追踪方法研究了花尾榛鸡的性比问题。首先,我们通过直接观测无线电标记雄性的配对比例,在消除可能的捕捉误差后,发现繁殖种群性比为1．26（即未配对的雄性占21％）。然后,我们估计了标记个体的存活率和繁殖成功率。在假设窝扩散时幼体的性比平衡的前提下,通过两性和两个年龄组（幼体,〈10月龄的个体;成体〉10月龄的个体）的确定性统计模型,得到的理论性比为1．22（即未配对的雄性占18％）,这一结果与实际观测的性比十分接近。我们认为,雌性死亡率高导致的两性存活率差异可以解释雄性性比偏高现象。我们进而讨论了花尾榛鸡整个分布区内居间强度的非对称性比的适应意义,以及在衰退的花尾榛鸡种群中雌性数量极端不足的后果[动物学报52（4）：655—662,2006]。     

黄毛鼠种群数量季节变动及其影响因素的研究

黄毛鼠是农业、卫生保健事业的主要害鼠之一,其种群数量的季节变动明显地表现为初春的数量上升,夏秋季低数量和冬季持续高数量3个阶段。数量消长曲线呈马鞍形。 菜地是黄毛鼠良好的栖息地,鼠密度终年多保持在较高的水平;旱地的鼠密度稍高;水田的鼠密度较低。 黄毛鼠种群数量的季节变动主要是种群的繁殖力和年龄组成变化的反映,同时又受到气候条件和农业生产活动的制约。