Migration of stored-grain insect pests from a small wheat bulk

Abstract

One hundred unsexed adults of each of the following coleopterous species were added to 27 .3 kg of clean wheat: Sitophilus oryzae (L.) (rice weevil), Rhyzopertha dominica (F.) (lesser grain borer), Tribolium castaneum (Herbst) (rust-red flour beetle), and the flat grain beetles Cryptolestes pusillus (Schonherr), C. ferrugineus (Stephens), and C. pusilloides (Steele and Howe). For 15 months, measurements were made of population size and emigration from this wheat bulk. The highest populations recorded for each species were: 138 850, 65 680, 9 060, 47 000, 15 530, 11 940, respectively, and total emigrant numbers during the period were: 774 682, 278 094, 123 784, 335 588, 39 070, 9 352, respectively. Such high numbers of emigrants in relation to relatively low source populations emphasize the significance of small amounts of infested grain as sources of infestation of large grain bulks, and hence the importance of grain hygiene. The proportion of females in the populations of four species changed significantly from 0.50 as populations developed. Emigration behaviour was influenced most commonly by temperature, insect numbers, and wheat age, but these factors did not act uniformly on all species. Negligible numbers of emigrants returned to the food source. Low numbers caught in food traps away from the source were consistent with these not being attractive but traps near the shed walls caught greater numbers than expected.

Outdoor flight activity and immigration of Rhyzopertha dominica into seed wheat warehouses

“…In Australia, Wright & Morton (1995) found that 16 °C was the minimum temperature threshold for flight, but Sinclair & Alder (1984) estimated a threshold of 21.5 °C. In Australia, Wright & Morton (1995) found that 16 °C was the minimum temperature threshold for flight, but Sinclair & Alder (1984) estimated a threshold of 21.5 °C.…”

“…Differences in the lower temperature threshold for R. dominica flight activity in the autumn vs. summer conditions may, in part, explain variable reports in the literature. In Australia, Wright & Morton (1995) found that 16 °C was the minimum temperature threshold for flight, but Sinclair & Alder (1984) estimated a threshold of 21.5 °C. Dowdy (1994) reported a lower flight threshold of 19.9 °C in the USA.…”

The spatiotemporal dynamics of Tribolium castaneum (Herbst): adult flight and gene flow

“…Both of these would influence the contribution of individual immigrants to gene flow. Tribolium castaneum beetles have been recorded emigrating from bags of flour in the laboratory (Hagstrum & Gilbert 1976) and from a small (<25 kg) artificially infested bulk of wheat (Sinclair & Alder 1984), but the situation in the field remains unclear. If females emigrate from grain storages in the field, they need to be characterized in terms of their survival rate, mating status and reproductive potential to understand how the movement of individual beetles relates to measures of gene flow obtained from the field.…”

Efficacy and limitations of phosphine "spot-fumigation" against five Coleoptera species of stored product pests in wheat in a grain store - short note

“…Mistargeting will result in untreated spots with pests, and infestation resurgence can be expected. Another potential problem associated with this method is that the emigrated (Sinclair & Alder 1984) and undetected pests in the vicinity of fumigated spots are treated inefficiently, and such exposure to low or sublethal gas doses poses a risk (Phillips et al 2001) that the most sensitive individuals from the population are eliminated, which will lead to an increase in PH 3 resistance.…”

“…We focused on the efficacy of PH 3 not only within the fumigated spot, but also in the surrounding areas because pests tend to migrate intensively in the grain. Sinclair and Alder (1984) documented that pests migrate in and outside stored grain mass even when populations are low.…”