Insect larvae typically moult to grow, but here we investigate insect larvae that moult to shrink; that is, retrogressive moulting or retrogressive development. We demonstrate this phenomenon in khapra beetle, Trogoderma granarium Everts (Dermestidae), among the world's most invasive pests of stored grains and cereal products, and a quarantine pest of interest for many countries. Larvae survived a 3‐month period of starvation, moulting up to six times and reducing their body mass by about half, on average. When reprovisioned with food, most larvae resumed the normal trajectory of development and pupated within a month. Thus, retrogressive development is a mechanism that may favour species whose resources exhibit feast‐or‐famine dynamics. By enabling survival during periods of privation, retrogressive development contributes to the invasiveness of the khapra beetle by allowing them to persist for long periods in empty storage facilities or empty containers used for international grain shipments.

The bean weevil, Acanthoscelides obtectus, is one of the most destructive insect pests of stored pulses globally. Cold treatment is a method used for controlling many insect species that are pests of stored-products. To understand if cold treatment can be used to control A. obtectus, we evaluated its cold tolerance at -5 & DEG;C and its supercooling point. Firstly, we measured the survival time of eggs, early instars, late instars, pupae, and adults at -5 & DEG;C using non-cold-acclimated insects, originally collected in Florida, USA. Secondly, we measured the survival time of late instars and adults at -5 & DEG;C using the strain from Florida and a strain from Ontario, Canada, and compared the effect of cold acclimation. To acclimate insects to cold, they were placed for 2 weeks at 15 & DEG;C followed by 2 weeks at 10 & DEG;C. The Florida strain had a slightly greater survival than the Ontario strain at -5 & DEG;C. Results show that at -5 & DEG;C, for non-cold-acclimated insects from the Florida strain, the most cold-sensitive stages were the eggs (LT50 of 2.3 d and LT95 of 5.3 d) and the pupae (LT50 of 1.6 d and LT95 of 6.0 d), whereas the late instars (LT50 of 4.0-4.8 d and LT95 of 8.2-8.7 d) were the most cold hardy stage. Cold acclimation increased insect survival time at -5 & DEG;C by several days. The egg was the stage with the lowest freezing point, with an average SCP of -27.7 & DEG;C. Therefore, all stages of A. obtectus would die instantaneously when exposed to this temperature. These results show that cold treatment can be used to control A. obtectus, particularly in Canada and other northernly regions where winter temperatures can be sustained below -5 & DEG;C for months and aeration fans can be used to blow cold ambient air into bins of stored pulses.

Solar heating disinfestation is a promising technique for low-income farmers in developing countries. Solar disinfestation of Sitophilus oryzae in wheat was investigated using clear and black polyethylene plastic bags and woven bags. Different amounts of wheat (16, 21, and 25 kg) with 12.2% moisture content (wet basis) were tested under two field conditions: 1) wheat bags were kept at the field with no stacking or mixing; 2) wheat bags were mixed at the end of the day and stacked during the night. The experiment was conducted in Canada and Egypt. Degree-minutes and time above 40 ? for each treatment were also calculated. Wheat inside clear polyethylene bags heated up to a temperature range of 40-55 ?, which is considered lethal to many stored-grain insects, including S. oryzae. Mortality of adult S. oryzae was 67.6 & PLUSMN; 30% for clear plastic bags and 4.3 & PLUSMN; 0.8% for woven plastic bags. In general, degree-minutes and time above 40 C inside 16 kg of wheat bags were significantly higher than bags with 21 or 25 kg of wheat.

Khapra beetle, Trogoderma granarium Everts, is one of the economically important quarantine pests that mainly feeds on food grain and proteinaceous materials. Its total development time lasts approximately 40-45 d under favorable environmental conditions. Extreme temperatures, high relative humidity (RH), high larval densities, or low food quality can induce a larval diapause, where the insect can survive for up to a few years, occasionally feeding and molting. Ecological modeling is a helpful tool to study the population dynamics of biological systems. Physi-Biological age method is based on temperature-driven development rate, and factors such as RH and food quality were considered as multipliers. The objective of this study was to develop mathematical models to calculate the survival and development of adults, eggs, larvae, pupae, and oviposition and diapause under different environmental conditions such as temperature, RH, and food quality. Algorithms were developed to simulate the population dynamics for each day and coded in C++. The developed models were validated against the literature data and evaluated using linear regression, R-2, and MSE. Population dynamics were simulated under Canadian grain storage conditions, and the developed models predicted that the diapausing larvae survived the extremely cold conditions found in Canadian grain. In contrast, other stages did not survive. The surviving larvae developed to pupae and adults, and females began laying eggs once the temperature became warmer in the grain bins.

Flat grain beetles (Coleoptera: Laemophloeidae) are common stored-product insect pests in Canada, infesting cereals in grain bins, equipment and end products in flour mills. We studied the cold tolerance of the three most common flat grain beetles: Cryptolestes ferrugineus, Cryptolestes turcicus and Cryptolestes pusillus, by measuring the survival at -10 degrees C and supercooling point (SCP) for different life stages (egg, young larva, old larva, pupa and adult) reared on flour mixed with brewer's yeast. Probit analysis was used to estimate the lethal time for 50 and 95% mortality. This was done with non-acclimated individuals (only held at 30 degrees C) or cold-acclimated individuals (held at 18, 10 and 5 degrees C, for 1 week/temperature). In general, adults were the most cold-hardy stage for each of the species. Acclimated insects were anywhere from no increase in cold tolerance to 14-fold more cold-tolerant than the corresponding non-acclimated stage and species. Cryptolestes ferrugineus was most cold-tolerant species (58 d at -10 degrees C to reach 95% mortality for acclimated adult), C. turcicus was the next most cold-tolerant, (39 d) and C. pusillus was the least cold-tolerant (11 d). The cold tolerance of adults reared on three diets was measured both for acclimated and non-acclimated insects. The adults reared on grain diet (whole wheat kernels, cracked wheat kernels and wheat germ (90:5:5 mass ratio) were the most cold-tolerant, adults reared on white-wheat flour and brewer's yeast diet (95:5 mass ratio) had the next highest cold tolerance followed by the adults reared on 100% white-wheat flour. Supercooling point (SCP) of insects ranged from -20.6 to -26.7 degrees C. In general, acclimated insects had slightly lower SCP than non-acclimated insects. Crown Copyright (C) 2021 Published by Elsevier Ltd. All rights reserved.

Heat treatment, an environmental friendly insect control method, has been applied to disinfest grain storage and food processing facilities. Movement of Tribolium confusum adults into grain piles (0.1, 0.5, 1.0, or 5.0 kg oat groats) was investigated at constant temperatures (30, 35, 37.5, 40, 45, or 50 degrees C) or rising temperatures (at a rate of 0.05 degrees C/min from 24 to 54 degrees C in laboratory, or from approximately 30 to 60 degrees C in a mill during a heat treatment). Adults moved among locations, paper surface, surface of grain pile and inside grain pile. There was preference for the grain at <= 37.5 degrees C. No single adult always stayed inside grain piles at 30 degrees C. At rising temperatures, adults preferred grain piles (on the surface of or inside grain piles) and moved into cold grain regardless of adult introduction methods (introduced on surface of groats piles, on paper, or premixed with groats). Rising temperatures did not drive adults out of grain piles during heat treatment. Crown Copyright (C) 2020 Published by Elsevier Ltd. All rights reserved.

Hemp, or industrial hemp (Cannabis sativa), is a high value alternative crop that has seen increases in production in Canada since commercial production was legalized in 1998. Insect infestation of stored hemp seed may result in loss of quality and value. There are few published studies on the ability of insects to survive and reproduce on hemp seed. Reproduction of eleven stored-product insects on hemp seed at different moisture contents with, or without dockage, was studied. Insects were introduced into 15 g of hemp seed at two initial moisture contents (dry, 9% m.c. or damp, 15% m.c.), two dockage levels (dockage-free or dockage, 15%), and held at 30 degrees C and 60-70% r.h. Five replicates of each treatment for each species were used. For beetles, twenty unsexed adults were used, for Ephestia kuehniella (Mediterranean flour moth), twenty eggs were used. For the beetles, live and dead adults were counted after 3, 5, 7 and 9 weeks, for the moth, adults were counted after 12.5 weeks. After counting, only live adults were returned to the hemp seed. The following beetle populations increased over the 9 weeks; Tribolium castaneum (red flour beetle), Lasioderma serricorne (cigarette beetle), Oryzaephilus surinamensis (saw-toothed grain beetle) and Trogoderma variabile (warehouse beetle). The following species did not increase their populations; Cryptolestes ferrugineus (rusty grain beetle), Rhyzopertha dominica (lesser grain borer), Sitophilus oryzae (rice weevil), Cryptolestes turcicus (flour mill beetle), Tribolium confusum (confused flour beetle), and Stegobium paniceum (drugstore beetle). For the beetles, higher dockage generally led to higher populations. The effect of moisture content was variable. Ephestia kuehniella produced adults on all treatments, with the dry treatment containing dockage performing the best. Crown Copyright (C) 2021 Published by Elsevier Ltd. All rights reserved.

Three new insecticide formulations were developed that combine diatomaceous earth (Celatom MN 23) with compounds with low mammalian toxicity. Sitophilus oryzae, Sitophilus granarius, Rhyzopertha dominica and Tribolium castaneum were held on wheat (13.5% moisture content) treated with different doses of the formulations at 28 +/- 1 degrees C and 60 +/- 5% RH for 2-7 days, and then held for progeny emergence. The three formulations were made up of: dill essential oil, bait, silica gel and DE (Dill-DE); pyrethrin, PBO, dill essential oil, silica gel and DE (Py-Dill-DE); and disodium octaborate tetrahydrate (DOT), pyrethrin, PBO, dill essential oil, silica gel and DE (DOT-PY-Dill-DE). They were applied either as powders or as slurries. Applying the formulations as powders over a range of concentrations showed that pure DE is the least effective insecticide, with 50% mortality ranging from 430 to 1000 ppm depending on the species after 2-3 days. Dill-DE formulation was the next least effective formulation. The Py-Dill-DE and DOT-Py-Dill-DE formulations had similar activity and being the most effective formulations with 50% mortality from 40 to 260 ppm depending on the species. Bioassays were also run at single doses. Dill-DE was applied at 300 ppm, Py-Dill-DE at 150 ppm and DOT-PY-Dill-DE at 200 ppm. After 3 days, Py-Dill-DE and DOT-PY-Dill-DE formulations there was 100% mortality for S. oryzae, S. granarius and R. dominica. After 7 days the mortality of T. castaneum was from 96 to 100%. Both formulations reduced the progeny almost by 100%. There was survival for all insects with Dill-DE formulation. The concentrations of 150 ppm of Py-Dill-DE, 200 ppm of DOT-PY-Dill-DE and 300 ppm of Dill-DE reduced bulk densities by 0.7, 0.8 and 5.7 kg/hL, respectively. Crown Copyright (C) 2020 Published by Elsevier Ltd. All rights reserved.

Whether stored-grain insects can communicate with each other inside stored-grain bulks is an important question for the development of pest management programs. Movements of the individual adults of Cryptolestes ferrugineus towards caged adult(s), in the presence or absence of wheat, were studied inside an apparatus (10 cm length), using an infrared camera. The numbers of the caged adults were 1, 20, or 50 of females or males, and 100 or 200 mixed-sex adults. Without grain, both males and females moved towards the caged single male, but not the caged single female. With grain, neither males nor females moved towards the caged single male or female. When 50 males were added to the cage, females did move significantly towards the caged males. There were trends for introduced males and females to move towards caged males at higher densities.

Khapra beetle, Trogoderma granarium Everts, is unusual in two key respects. First, they are among the most cold hardy of stored-product insect pests even though they originate in hot and dry regions of the Indian subcontinent. Second, their larvae can enter into diapause to survive harsh environmental conditions. In the present study, we examined whether these two phenomena are related, i.e., due to cross-tolerance. Cross-tolerance is the tolerance to one ecological stress when induced by a separate stress. To investigate this, khapra beetle larvae were reared at different relative humidities (3, 28, 49, and 79%) in either nondiapausing or diapausing conditions. Then the cold tolerance of larvae was estimated by measuring mortality after different durations at -10°C. For nondiapausing larvae, relative humidity had little effect on cold tolerance with the lethal time to 50% mortality (LT50) occurring between 2 and 4 d. For diapausing larvae, cold tolerance increased with greater desiccation stress with LT50's of 5, 7, 10, and 18 d at 79, 49, 28, and 3% RH, respectively. This suggests that the physiological mechanisms that protect diapausing larvae from desiccation may also increase cold tolerance, even though these insects may rarely be exposed to low temperatures.

Larvae of khapra beetle, Trogoderma granarium (Coleoptera: Dermestidae) have an unusual diapause during which they may sporadically feed for several years, but not complete development. Diapausing larvae have an enhanced tolerance to starvation, insecticides and extreme temperatures. Thus, knowledge of factors that terminate larval diapause may aid in the control of this pest. In the current study, we assessed the effect of diet quality (five mixtures of fresh and spent diet in a replacement series) on diapause termination for diapausing larvae from laboratory cultures aged 3, 10, or 14 months. Larvae (n = 10 replicates for each combination of diet quality and culture, 10 larvae/replicate) were held at 30 degrees C and observed at different intervals over the course of 188 days to record larval mortality and larval pupation (= diapause termination). Larvae were least able to survive on diets of lower quality; i.e., 88% mortality after 188 days on 0% fresh diet versus 8% mortality on 100% fresh diet (averaged across cultures). Larvae were most likely to terminate diapause on diets of higher quality; i.e., 87% termination after 188 days on 100% fresh diet versus 0% termination on 0% fresh diet (averaged across cultures). Diapausing larvae from older cultures were least likely to terminate diapause and least likely to survive. On 100% fresh diet, diapause termination of larvae from cultures aged 3, 10 and 14 months was 93, 91, and 78%, respectively. On 0% fresh diet, mortality of larvae from cultures aged 3, 10 and 14 months was 67, 97, and 100%, respectively. These results indicate that diapausing larvae can accumulate the nutrients required to terminate diapause and complete development when provided with an opportunity to do so. However, the window of opportunity continues to shrink the longer the larvae remain in diapause. Crown Copyright (C) 2019 Published by Elsevier Ltd. All rights reserved.

Safe storage times of hemp seeds (cultivar: FINOLA (R)) were studied by storing the hemp seeds with three dockage levels (0, 5, and 15%) at four temperatures (20, 25, 30 and 35 degrees C), four relative humidities (50, 63, 75, and 92%) for up to 26 wk. To evaluate the safe storage time, the following storage parameters were measured or determined: seed germination, free fatty acid value (FAV) of seeds, and visible and invisible mold. Dockage percentages did not significantly influence equilibrium moisture content, FAV, germination loss and the time of the first appearance of visible and invisible mold and number of kernels infected by storage fungi. This non-influence was caused by the experimental setup because the heat and water produced by the spoiled hemp seeds with dockage were diffused out of the 1 kg sample. Hemp seeds with 15% dockage had slightly faster germination loss than that with lower percentages of dockage. The FAV of hemp seeds had a negative correlation with germination. Based on the time for 20% initial germination losses, the safe storage guidelines of stored bulks of hemp seeds were developed and mathematically modelled. The recommended safe storage moisture content was 8% under Canadian conditions. At 25 degrees C, the safe storage time was 20.8 and 2.8 wk if the hemp seeds without dockage had 8% and 14% moisture contents, respectively. Crown Copyright (C) 2019 Published by Elsevier Ltd. All rights reserved.

Khapra beetle, Trogoderma granarium Everts, is one of the world's most important pests of stored grain. Common in Africa and Asia, it is a quarantine insect for much of the rest of the world where methyl bromide has traditionally been used for its control. However, this ozone-depleting fumigant is now heavily restricted, and alternate methods of control are required. In a two-step process, we examined the use of high-temperature exposure as one such method of control. First, different life stages were held at 45°C for different periods to calculate LT50 (lethal time to 50% mortality) values. In descending order, the most heat-tolerant life stages at 45°C were diapausing larvae (LT50 = 41 - 122 h) > nondiapausing larvae (LT50 = 47 h) > adults (LT50 = 33 h) > pupae (LT50 = 25 h) > eggs (LT50 = 10 h). Second, diapausing larvae (the most heat-tolerant stage) were held at 45, 50, 55, and 60°C for different periods to calculate LT50, LT95, LT99, and probit 9 (99.9968% mortality) values. Estimated LT99 values for diapausing larvae were 288 h at 45°C, 6 h at 50°C, 1.1 h at 55°C, and 1 h at 60°C. Based on these results, an exposure of 2 h at 60°C is recommended to control T. granarium with high temperatures. To meet requirements for control of quarantine pests, exposure of between 2 and 12 h at 50-60°C is recommended to cause probit 9 mortality, but additional experiments are needed to get a better estimate of probit 9.

Population dynamics of rusty grain beetle, Cryptolestes ferrugineus (Stephens; Coleoptera: Cucujidae), was studied using different sizes of grain bulks (patches) at various temperatures. The temperatures were 21, 25, 30, 35°C, T-decrease (30°C in the first 4 wk and then decreased 1°C /wk), and T-increase (21°C in the first 2 wk and then increased 1°C /wk). Number of adults and offspring and infested wheat kernels were counted every 4 wk up to 24 wk (31 wk for the T-decrease). The grain bulk patches used were: small (50 ml inner volume, 0.03 kg wheat), medium (2.6 liters inner volume, 2 kg wheat), and large (18 liters inner volume, 14 kg wheat). All of the correlation coefficients between the insect numbers and kernel infestation percentage were ≥0.63. Two types of the population dynamic curves were observed: insect number or density continually increased with time during the entire experiment, or there was a rise then a fall in insect number or density over time, giving a peak number or density. The peak insect density was approximately 400 to 500 adults/kg of wheat for all patches at 30°C or lower. At 35°C, the peak densities of live adults were 3,956 ± 630, 2,094 ± 34, and 1,003 ± 70 adults/kg of wheat in small, medium, and large patches, respectively. Patch size influenced insect population dynamics at 35°C. Insect number inside large patch was more dependent on the previous insect number than that inside small patches.

172 Julius-Kühn-Archiv 463 Suitability of hemp seed for reproduction of stored-product insects Kim Stadnyk1, Noel D.G. White1, Fuji Jian2, Paul G. Fields1 1Morden Research and Development Centre, Agriculture and Agri-Food Canada, kim.stadnyk@agr.gc.ca, noel.white@agr.gc.ca, paul.fields@agr.gc.ca 2 Biosystems Engnineering, University of Manitoba, Winnipeg, MB, Canada, jianf@cc.umanitoba.ca DOI 10.5073/jka.2018.463.041

Several studies have examined the toxicity of aflatoxin B-l to insects, but there have been very few studies on insects that are regularly exposed to this mycotoxin as part of their diet. Research reported the effect of the mycotoxin aflatoxin B-1 in the diet on the fungus grain beetle, Ahasverus advena (Waltl), which is often found in moldy grain. The effects of aflatoxin B-1 in diet on developmental time, survival rate and fecundity of A. advena were evaluated with artificial diets containing 0 to 16,000 ppm aflatoxin B-1. Aflatoxin B-1 increased one-day-old larvae developmental time at concentrations as low as 2000 ppm and increased larval mortality at concentration as low as 500 ppm. For one-day old larvae, there was 99% mortality at 8000 ppm. The LD50 for the one-day-old larvae, five-day-old larvae and adults were 1671, 2696, and 5768 ppm, respectively. The total number of offspring declined to 38 offspring at 4000 ppm aflatoxin B1 compared with 151 offspring in the untreated controls. Ahasverus advena was much less sensitive to aflatoxin B-1 by 200-2000 times higher than other insects and other animals. Crown Copyright (C) 2018 Published by Elsevier Ltd. All rights reserved.

Predicting the occurrence of insects with a high accuracy requires the estimation of insect development time and the variation among individuals for each life stage and species under different environmental conditions such as fluctuating temperature, variation of relative humidity, different body sizes and stages of the insects, levels of crowding, and food supply. This review summarized the modeling methods of population dynamics of insects with several distributions of insect development, assumption and prediction accuracy of these developed models, and disadvantages and advantages of these modelling methods. These modeling methods include degree day model, nonlinear model, and distribution delay models. The structure of most common models are cohort, Leslie matrix, simulation, and individual based. The relationships among the modeling assumptions, effects of temperature, and other environmental factors, and structures of the developed models were examined. A new modelling approach such as physiological-biological time scale and chaos theory was suggested.

Data collected in Part I of this study were further analyzed by using mathematical modeling methods. Out of the nine unstructured population models tested, no model could fit the insect numbers under all of the tested conditions. This analysis showed that Cryptolestes ferrugineus (Stephens) (Coleoptera: Laemophloeidae) inside small patches (50 ml volume) had different characterization of population dynamics from that inside large patches (18 liter volume) and had different population demography when the insect number at the previous time was different. The key factor analysis showed that the first two main factors influencing the population dynamics were the temperature and the previous insect numbers. The total numbers of insects increased with the increase of sum of degree days. However, the degree day model developed based on the constant temperatures could not predict insect numbers under fluctuating temperatures. A newly developed model, which used the result of the unstructured population models, key factor analysis, and the degree day model, could explain about 66% of the insect numbers under fluctuating temperature conditions.