Cold treatment enhances low‐temperature flight performance in false codling moth,Thaumatotibia leucotreta (Lepidoptera: Tortricidae)

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Mating frequency of female false codling moth,Thaumatotibia leucotreta (Lepidoptera: Tortricidae): trade-off between fecundity and longevity

Journal of Insect Behavior - Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae) is a polyphagous insect pest native to sub-Saharan Africa. The larvae burrow into the fruit and...     

False codling moth Thaumatotibia leucotreta (Lepidoptera,Tortricidae) larvae are chill‐susceptible

Abstract This study reports on the low temperature tolerance and cold hardiness of larvae of false codling moth, Thaumatotibia leucotreta. We found that larvae have mean critical thermal minima (lower limits of activity) of 6.7°C which was influenced by feeding status. The effects of low temperature exposure and duration of exposure on larval survival were assessed and showed that the temperature at which 50% of the population survives is ?11.5 ± 0.3°C after 2 h exposure. The supercooling point (SCP, i.e., freezing temperature) was investigated using a range of cooling rates and under different conditions (feeding and hydration status) and using inoculative freezing treatments (in contact with water or orange juice). The SCP decreased significantly from ?15.6°C to ?17.4°C after larvae were fasted for 24 h. Twenty‐four hour treatments at either high or low relative humidity (95.9% or 2.4%) also significantly decreased SCP to ?17.2°C and ?18.2°C respectively. Inoculative freezing (by water contact) raised SCP from ?15.6°C to ?6.8°C which could have important implications for post‐harvest sterilization. Cooling rates did not affect SCP which suggests that there is limited phenotypic plasticity of SCP during the larval life‐stage, at least over the short time‐scales investigated here. In conclusion, larvae of T. leucotreta are chill‐susceptible and die upon freezing. These results are important in understanding this pest's response to temperature variation, understanding pest risk status and improving post‐harvest sterilization efficacy.     

Entomopathogenic nematodes from north-eastern South Africa and their virulence against false codling moth,Thaumatotibia leucotreta (Lepidoptera: Tortricidae)

A survey was undertaken to determine the diversity and frequency of endemic entomopathogenic nematodes (EPN) in subtropical regions in the Mpumalanga, Limpopo and KwaZulu-Natal provinces of South Africa. A total of 136 soil samples were randomly taken from cultivated and uncultivated habitats, including subtropical fruit tree orchards (avocado, litchi, macadamia, mango and guava) and adjoining natural vegetation. EPNs were isolated from 14 samples (10.3%) by means of baiting with Tenebrio molitor larvae. Heterorhabditis was the most common genus isolated from 12 samples, whereas only two Steinernema species were isolated. The most common Heterorhabditis isolated were Heterorhabditis noenieputensis and H. zealandica, which were both isolated from four samples each. The present report is the first occurrence of H. taysearae and H. baujardi in South Africa. The two Steinernema species are both unknown species. Laboratory bioassays were conducted to determine the potential of seven native EPN isolates to control the false codling moth (Thaumatotibia leucotreta) (FCM). Last instar FCM larvae were found to be most susceptible to S. yirgalemense (157-C), H. zealandica (WS 23) and Steinernema litchii (WS9), when exposed to 50 IJs/50?µ? water for 48?h, causing 100%, 94.2% and 93.5% mortality, respectively.     

Bio-ecology of false codling moth,Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae) within citrus orchards in Kenya and Tanzania

1. False codling moth, Thaumatotibia leucotreta is among the key constraints of the agricultural industry. Little is known about the population dynamics and genetic diversity of this pest in East Africa.
2. The spatial–temporal population dynamics and genetic diversity of false codling moth were evaluated in citrus orchards in Kenya and Tanzania between May 2017 and August 2018 covering two fruiting seasons. The diversity of false codling moth sampled in these orchards and from solanaceous hosts, as well as from specimens received from Uganda, Sudan, and South Africa were assayed using the mitochondrial cytochrome oxidase I gene.
3. A similar spatial–temporal pattern of false codling moth was found in both Kenya and Tanzania, with the most male moths in August 2017 and 2018. In Tanzania, the number of male moths caught at high and mid altitudes did not differ but were significantly higher than those caught at low altitude.
4. A relatively low false codling moth genetic diversity was recorded at the sites where sampling was done in the respective countries as well as between specimens sampled from different host plants.
5. The low false codling moth genetic diversity determined in this trial can be exploited in the management of the pest in the studied countries.

     

Thermal limits to survival and activity in two life stages of false codling moth Thaumatotibia leucotreta (Lepidoptera,Tortricidae)

The present study examines life stage‐related variation in the thermal limits to activity and survival in an African pest, the false codling moth Thaumatotibia leucotreta (Lepidoptera, Tortricidae). Thermal tolerance, including the functional activity limits of critical thermal maxima and minima (CT_max and CT_min respectively), upper and lower lethal temperature, and the effect of heat and cold hardening (short‐term acute plasticity), is measured across a diverse range of low or high temperature stress conditions in both larvae and adults. We also report the sum of inducible and cognate forms of the amounts of heat shock protein 70 (HSP70) as an explanatory variable for changes in thermotolerance. The results show that the larvae have high variability in CT_max and CT_min at different ramping rates and low levels of basal (innate) thermal tolerance. By contrast, the adults show high basal tolerance and overall lower variability in CT_max and CT_min, indicating lower levels of phenotypic plasticity in thermotolerance. HSP70 responses, although variable, do not reflect these tolerance or survival patterns. Larvae survive across a broader range of temperatures, whereas adults remain active across a broader range of temperatures. Life stage‐related variation in thermal tolerance is most pronounced under the slowest (most ecologically‐relevant) ramping rate (0.06 °C min^–1) during lower critical thermal limit experiments and least pronounced during upper thermal limit experiments. Thus, the ramping rate can hinder or enhance the detection of stage‐related variation in thermal limits to activity and survival of insects.     

The impact of naturally occurring entomopathogenic nematodes on false codling moth,Thaumatotibia leucotreta (Lepidoptera: Tortricidae), in citrus orchards

The impact of naturally occurring entomopathogenic nematodes (EPNs) on Thaumatotibia leucotreta was studied in a citrus orchard in Nelspruit, South Africa. Fruit infestation by T. leucotreta was 58.6% lower (P < 0.05) in an orchard block where EPN was conserved compared to a block where EPN was suppressed by nematicide (cadusafos) application.     

Sex‐dependent thermal history influences cold tolerance,longevity and fecundity in false codling moth Thaumatotibia leucotreta (Lepidoptera: Tortricidae)

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Radiation biology and inherited sterility in false codling moth (Lepidoptera: Tortricidae)

False codling moth, Cryptophlebia leucotreta (Meyrick), male and female mature pupae and newly emerged adults were treated with increasing doses of gamma radiation and either inbred or out-crossed with fertile counterparts. For newly emerged adults, there was no significant relationship between dose of radiation and insect fecundity when untreated females were mated to treated males (N female by T male). However, fecundity of treated females mated to either untreated (T female by N male) or treated males (T female by T male) declined as the dose of radiation increased. A similar trend was observed when mature pupae were treated. The dose at which 100% sterility was achieved in treated females mated to untreated males (T female by N male) for both adults and pupae was 200 Gy. In contrast, newly emerged adult males treated with 350 Gy still had a residual fertility of 5.2% when mated to untreated females, and newly emerged adult males that were treated as pupae had a residual fertility of 3.3%. Inherited effects resulting from irradiation of parental (P1) males with selected doses of radiation were recorded for the F1 generation. Decreased F1 fecundity and fertility, increased F1 mortality during development, and a significant shift in the F1 sex ratio in favor of males was observed when increasing doses of radiation were applied to the P1 males.     

Termination of the facultative diapause in the codling moth, Laspeyresia pomonella (Lepidoptera, Tortricidae)

The abiotic factors regulating the termination of the facultative diapause of the mature larva of the codling moth, Laspeyresia pomonella (L.), are described. The termination of diapause under long-day conditions (LD) is influenced by: (i) the rearing temperature of the larvae during prediapause development, (ii) the duration of the preincubation period, i.e. the time for which the diapausing larvae remain under prediapause rearing conditions, (iii) the reactivating incubation, i.e. the period for which the larvae are chilled, and (iv) the complementary incubation (LD and, except in one experiment, 26°), i.e. the period after the chilling needed for the pupation of the insects. The complementary incubation is distinctly shorter if the prediapause development of the larvae takes place at rearing temperatures below 26°, i.e. 21° or 19°. The latter conditions led to 100% pupae and pupation could be accelerated by prolonging the preincubation period. In larvae reared at 26°, the prolongation of the preincubation period raised the rate of pupation to a maximum of only 56% and also caused higher mortality. On the other hand, diapause was terminated under short-day conditions if the temperature was raised to 26° after a rearing temperature of 19° and a preincubation period of 90 days.

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Beendigung der fakultativen diapause des apfelwicklers, Laspeyresia Pomonella (Lepidoptera, Tortricidae)

Zusammenfassung Es wurde untersucht, welche abiotischen Faktoren die Beendigung der fakultativen Diapause ausgewachsener Apfelwicklerlarven (Laspeyresia pomonella) steuern. Die Beendigung der Diapause unter Langtagbedingungen (LT) wird beeinflusst durch: 1. die Zuchttemperatur der Larven während der Prädiapauseentwicklung; 2. die Dauer der Präinkubation, d.h. die Zeit, während der diapausierende Larven unter Prädiapause-Zuchtbedingungen bleiben; 3. die Reaktivierungs-inkubation, d.h. eine Periode von 70 d, während der die Larven auf 4° gekühlt werden und 4. die Komplementärinkubation (LT und, ausser in einem Experiment, 26°), d.h. die nach der Kühlung bzw. dem Wechsel in der Photoperiode benötigte Zeitdauer bis zur Verpuppung. Die Komplementärinkubation ist deutlich kürzer, wenn die Prädiapauseentwicklung der Larven bei Temperaturen unter 26° stattfindet. Bei 19° verpuppten sich 100% der Larven, wobei der Zeitpunkt der Verpuppung durch die Verlängerung der Präinkubationszeit beschleunigt wurde. Bei Larven, die bei 26° gezüchtet wurden, erreichte die Verpuppungsrate lediglich 56% bei einer relativ langen Präinkubationsdauer, wobei deren Verlängerung auch die Larvenmortalität erhöhte. Nach einer Zuchttemperatur von 19° und einer Präinkubationsdauer von 90 Tagen konnte die Diapause unter Kurztagbedingungen beendet werden, wenn die Temperatur auf 26° erhöht wurde.

     

Baseline monitoring of codling moth (Lepidoptera: Tortricidae) larval response to benzoylhydrazine insecticides

A diet-incorporation larval bioassay was developed to measure the response of codling moth, Cydia pomonella (L.), to the benzoylhydrazine insecticides tebufenozide and methoxyfenozide. The bioassay tested neonates and third, fourth, and fifth instars from a laboratory colony and neonates and fourth instars from a pooled population collected from five certified-organic apple orchards. Bioassays were scored after 6 and 14 d. No differences between the laboratory and field population were found for either insecticide. Significant differences were found in the response of third and fifth instars between the 6 and 14 d bioassays, primarily due to a high proportion of moribund larvae in the shorter assay. Larval age had a significant effect in bioassays and was more pronounced in 6- versus 14-d tests. Fifth instars were significantly less susceptible to both insecticides than other stages, while responses of third and fourth instars were similar. The response of neonates was significantly different from third and fourth instars to tebufenozide but not with methoxyfenozide in the 14-d test. Field bioassays excluded the use of fifth instars and were scored after 14 d. LC50s estimated for 18 field-collected populations varied five- and ninefold for tebufenozide and methoxyfenozide, respectively. The responses of all but six field-collected populations were significantly different from the laboratory strain. Five of these six populations were collected from orchards with no history of organophosphate insecticide use. The LC50 for methoxyfenozide of one field-collected population reared in the laboratory for three generations declined fourfold, but was still significantly different from the laboratory population. These data suggest that transforming current codling moth management programs in Washington from a reliance on organophosphate insecticides to benzoylhydrazines may be difficult.     

Correlated insecticide cross-resistance in azinphosmethyl resistant codling moth (Lepidoptera: Tortricidae)

Resistance to several classes of insecticides was correlated with azinphosmethyl resistance in codling moth, Cydia pomonella (L.), in California. In tests of laboratory and field populations, cross-resistance was positively correlated with azinphosmethyl and two organophosphates (diazinon, phosmet), a carbamate (carbaryl), a chlorinated hydrocarbon (DDT), and two pyrethroids (esfenvalerate and fenpropathrin). Additionally, negatively correlated cross-resistance was identified between azinphosmethyl and two other organophosphates, chlorpyrifos and methyl parathion. Patterns of resistance observed in laboratory colonies were confirmed with field bioassays. In bioassays of field populations, azinphosmethyl resistance was observed to increase from 1991 to 1993, although levels of resistance remained < 13-fold. Because orchards with azinphosmethyl resistance have had difficulties with suppression of codling moth, and cross-resistance was found for all tested classes of insecticides, strategies for managing resistance will need to be developed so as to protect current and future control tactics. The two insecticides with negatively correlated cross-resistance are discussed as potential tools for resistance management.     

Seasonal susceptibility of 'Bartlett' pears to codling moth (Lepidoptera: Tortricidae) infestation and notes on diapause induction

Seasonal susceptibility of 'Bartlett' pear, Pyrus communis L., to codling moth, Cydia pomonella (L.), infestation, successful completion of larval development after infestation, and the induction of C. pomonella diapause was studied from 1992 through 1995. The seasonal variation in C. pomonella infestation and larval survival were effected by changes in fruit maturity. In late May through mid-June, pears were hard and were not as successfully infested by C. pomonella and produced less larvae compared with fruit later in the season. In late June to mid-July, pears became more suitable for infestation and a greater percentage of the larvae completed their development. In late July through mid-August, pears were susceptible to infestation, but the larvae were less likely to successfully complete development than in the late June to mid-July period due to pear tissue breakdown. From mid-August through September, pears are unsuitable for infestation, and few larvae were produced. When fruit were infested with neonate larvae in late May and mature larvae emerged from the fruit in July, a low percentage of the larvae entered diapause. However, when fruit were infested with neonate larvae in early July and mature larvae emerged from the fruit in early August, the majority of the larvae entered diapause. When fruit were infested with neonate larvae in late July through September and mature larvae emerged from the fruit after mid-August, nearly all C. pomonella larvae had entered diapause.     

Mating compatibility among populations of codling moth Cydia pomonella Linnaeus (Lepidoptera: Tortricidae) from different geographic origins

The codling moth Cydia pomonella (Linnaeus) (Lepidoptera: Tortricidae) is a serious pest of pome fruit worldwide and the sterile insect technique (SIT) provides an environmentally acceptable approach for its control. As the pest is present in both the southern and northern hemispheres it would be possible for a rearing facility in the northern hemisphere to supply sterile moths to an SIT programme in the southern hemisphere during the northern winter and vice versa. This could greatly improve the economics of moth production and the running costs of rearing facilities. However in order to develop this concept, it is important to assess if populations of codling moth from different geographical regions share mating compatibility. Twelve different laboratory and field populations from both hemispheres were sampled and field cage bisexual mating compatibility tests were carried out between selected combinations. The index of sexual isolation (ISI) and the female and male relative performance index (FRPI and MRPI, respectively) were calculated for each mating combination. In only two of the combinations was there a slight but significant deviation from random mating. There were also some significant differences in mating duration between the homotypic matings and the duration of a particular homotypic mating seemed to depend on the origin of the other population in the cage. It was concluded that there exist no barriers to mating between populations of codling moth from many parts of the world and that it would be feasible for sterile moths to be shipped from one rearing facility to SIT programmes in other parts of the world.     

Toxicity and residual activity of methoxyfenozide and tebufenozide to codling moth (Lepidoptera: Tortricidae) and oriental fruit moth (Lepidoptera: Tortricidae)

A series of studies were conducted to examine the residual activity and toxicity of the ecdysone agonists tebufenozide and methoxyfenozide to codling moth, Cydia pomonella (L.), and oriental fruit moth, Grapholita molesta (Busck), in North Carolina apple systems. Methoxyfenozide exhibited greater activity than tebufenozide against codling moth eggs in dose-response bioassays, with a 4.5- and 5.3-fold lower LC50 value to eggs laid on fruit treated before or after oviposition, respectively. Oriental fruit moth eggs were 57- and 12-fold less sensitive to methoxyfenozide than were codling moth eggs on fruit treated before and after oviposition, respectively. Methoxyfenozide was effective in reducing larval entries of both codling moth and oriental fruit moth in field residual activity bioassays, exhibiting activity for at least 28 d after application. Residue breakdown on fruit was approximately 80% at 28 d after treatment for both methoxyfenozide and tebufenozide, with the most rapid residue decline (60%) occurring during the first 14 d after application. Two applications of methoxyfenozide applied at 14-d intervals provided better canopy coverage and higher residue levels than one application. Spray volume (683 versus 2,057 liters/ha) did not affect the efficacy of methoxyfenozide. Leaf and fruit expansion during the season was measured to determine potential plant-growth dilution effects on residual activity. There was very little increase in leaf area after mid May, but increase in fruit surface area over the season was described by a second order polynomial regression. Implications for codling moth and oriental fruit moth management programs are discussed.     

Low-temperature tolerance of false codling moth Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae) in South Africa

(1) The low-temperature tolerance of false codling moth (FCM) Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae) is a significant aspect of this pest's population dynamics and has implications for post-harvest control and sterile insect technique programs.

(2) Here, we report results of experiments examining the effects of time, temperature and their interactions on low-temperature tolerance in adult FCM. In addition, using a variety of thermal pre-treatments, we examine the potential for hardening responses over several hours to improve low-temperature tolerance in FCM.

(3) Lower lethal temperature assays showed significant effects of time, temperature and significant interactions between time and temperature on survival (p<0.0001 in all cases). The temperature at which the probability of survival of 50% of the FCM population after 2 h of exposure was −4.5 °C, which varied significantly to −0.5 °C in 10 h. Gender and early adult age did not affect low-temperature tolerance of FCM.

(4) Using a range of non-lethal, low- and high-temperature pre-treatments, FCM survival could not be increased (p>0.84) and thus limited evidence for rapid cold hardening was found. These results are discussed with respect to microclimate temperatures in typical FCM environments and have implications for understanding population dynamics in this species and the diversity of low-temperature responses of insects.

The role of abiotic factors in the pupation of Thaumatotibia leucotreta Meyrick (Lepidoptera: Tortricidae) in the soil

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Tebufenozide targeted against codling moth (Lepidoptera: Tortricidae) adults, eggs, and larvae

The effectiveness of tebufenozide applied against the adult, egg, and larvae of codling moth, Cydia pomonella (L.), was evaluated. Significant reductions in fecundity and egg hatch occurred after 1-h and 24-h exposures of females and 24-h exposures of males-only to residues in plastic plates. A significant reduction in egg hatch was also found after a 1-h exposure of males. The ovicidal effects of tebufenozide in field trials did not significantly differ for eggs laid on residues or treated topically. Corrected egg mortality exceeded 95% for cohorts laid <130 degree-days after sprays were applied. Fecundity and egg hatch were measured after either a 24-h exposure of moths or a 10-d exposure of moths and eggs on apple trees. Significant reductions in both fecundity and fertility occurred compared with an untreated control up to 7 d in the 24-h assays and accounted for 60-70% fewer larvae produced per mated female. The mean numbers of larvae produced per mated female after the 10-d exposure were reduced 100-75% in assays started on day 0-21 after the spray application compared with the untreated control. Fecundity was significantly reduced for 7 d and egg hatch was reduced for the entire 21-d test period in these trials. Residues had a 14-d half-life on apple foliage. Residues applied to foliage or to foliage and fruit did not significantly increase the proportion of uninjured fruit compared with the untreated control in bioassays where neonates were placed on foliage 10 cm from fruit. However, the proportion of injured fruits with shallow stings versus deep entries was higher on the treated versus the untreated plants. Field applications of tebufenozide reduced fruit injury >90% when applied early during emergence. Plots treated after the beginning of egg hatch had a larger proportion of injured fruits with shallow larval feeding.     

Pheromone pre-exposure and mating modulate codling moth (Lepidoptera: Tortricidae) response to host plant volatiles

Abstract 1 Two codling moth Cydia pomonella kairomonal attractants, ethyl (E,Z)‐2,4‐decadienoate (pear ester) and (E)‐β‐farnesene, were tested in an insecticide‐sprayed apple orchard and an orchard treated for mating disruption with synthetic pheromone (E,E)‐8,10‐dodecadienol (codlemone). Male captures with pear ester were higher in the pheromone‐treated than in the insecticide‐treated orchard, whereas captures with (E)‐β‐farnesene were not different. Subsequent wind tunnel experiments confirmed that pre‐exposure to sex pheromone codlemone increased the behavioural response of codling moth males to pear ester. This supports the idea that male attraction to the plant volatile pear ester and sex pheromone codlemone is mediated through the same sensory channels. 2 Pear ester is a bisexual codling moth attractant and even captures of female moths were significantly increased in the pheromone‐treated orchard. In the laboratory wind tunnel, pheromone pre‐exposure had no effect on female response to pear ester, but significantly more mated than unmated codling moth females flew upwind towards a pear ester source. Differences in mating status in insecticide‐treated vs. pheromone‐treated orchards may thus account for the differences in female trap captures with pear ester. 3 These findings are important with respect to monitoring of codling moth with pear ester in mating disruption orchards. They also emphasize the importance of host plant volatiles in pheromone‐mediated mating disruption, which has been neglected to date.     

Isolation of microsatellite loci in the codling moth,Cydia pomonella (Lepidoptera: Tortricidae)

Cydia pomonella L. is an important insect pest of pome fruits worldwide. We have isolated and characterized 17 microsatellite loci from the enriched genomic libraries constructed using a biotin/streptavidin capture protocol. Among these loci, 11 were scored polymorphic when 50 individuals from a laboratory population were screened. Their alleles numbered two to four, with the observed heterozygosity (H_O) ranging from 0.114 to 0.404. Successful amplification was obtained for all these loci when the designed primers were tested, showing the promise of use in genetic mapping and population studies.