Estimation of lethal times of supra-optimal temperatures against adults of five stored-product insect pests

The escalating concerns regarding the adverse effects link to pesticide utilization against stored-product pests have amplified interest in exploring safer alternative approaches, notably physical methods. Temperature management, a prominent avenue within physical control, is considered one of the most promising strategies against these pests. This investigation scrutinizes the effectiveness of elevated temperatures on adult Trogoderma variabile, Callosobruchus maculatus, Lasioderma serricorne, Oryzaephilus surinamensis), and Plodia interpunctella.

Experiments employed one-day-old adults. High temperatures (40, 43, 46, 50 and 54 °C) were regulated using an electric oven (Memmert, Germany). Initially, each species underwent individual assessment in preliminary tests, establishing eight exposure durations for the main bioassays. Within each exposure duration, groups of one-day-old adults (4 replicates, comprising 25 male and 25 female adults per replicate) were housed in glass Petri dishes. Upon completion of the exposure period, adults were relocated to ambient room conditions (21-27 °C; 55-70% R.H.). Subsequently, deceased males and females were tallied after a 24-hour interval.

Both male and female adults across all species exhibited equivalent sensitivity to supra-optimal temperatures. As anticipated, higher temperatures significantly reduced the LTs; however, distinct response patterns were observed among the studied species. At 40 °C, the LT50s for T. variabile, C. maculatus, L. serricorne, O. surinamensis, and P. interpunctella were approximately 18, 9, 47, 34, and 7.5 h, respectively. At 54 °C, these times decreased to about 7, 4, 12, 8 and 8 min, respectively. Correspondingly, the LT95s at 40 °C these pests were approximately 3.7, 4.8, 5.7, 5.5, and 1.9 days, respectively, whereas at 54 °C, they reduced substantially to about 20, 18, 23, 14, and 26 min, respectively. For T. variabile, the LT50s at 43, 46, and 50 °C (approximately 13, 11.3, and 11 min, respectively) were roughly 1.7 times longer than that at 54 °C (around 7 min). Conversely, at 40 °C, the LT50 was considerably lengthier (1077 min). C. maculatus adults displayed LT50 values at 46 and 50 °C (around 8 and 9 min, respectively), roughly twice as long as those at 54 °C (4 min). At 40 and 43 °C, the LT50s were notably longer (543 and 67 min, respectively). In the case of L. serricorne, solely the LT50 at 50 °C was approximately twice as long as that at 54 °C (approximately 12 min). At 43 and 46 °C, however, the requisite LT50s were lengthier (about 167 and 80 min, respectively), while at 40 °C, the LT50 was substantially longer (about 2820 min). For O. surinamensis adults, the LT50s at 43, 46, and 50 °C were approximately 1.3 to 1.5 times longer (about 13, 12, and 11 minutes, respectively) than that at 54 °C (about 8 min, with the LT50 at 40 °C being notably longer (about 2048 min). Concerning P. interpunctella, the LT50s at 46 and 50 °C were roughly three (about 27 min) and two (about 18 min) times greater than the LT50 at 54 °C (about 8 min). At 40 and 43 °C, the LT50s were considerably longer (about 449 and 98 min, respectively). In general, based on both LT50 and LT95 L. serricorne emerged as the most tolerant species, while C. maculatus, according to LT50 and O. surinamensis based on LT95 appeared to be the most sensitive species to high temperatures.

Despite the varied responses observed among adult stored-products insects to supra-optimal temperatures, the comparison between estimated LT50s and LT95s indicated the notable efficacy of high temperatures, particularly at 50 and 54 °C, in inducing substantial mortality rates. This effectiveness ranged from approximately 23 min for L. serricorne to 14 min for O. surinamensis, resulting in 95% mortality. Our findings underscore the potential of high temperatures as a pivotal tool in the management and mitigation of economic losses caused by the five studied pests. The outcomes of this research advocate for the significant role that elevated temperatures can play in addressing these pests. Considering our results in conjunction with existing reports on the effects and efficiency of high temperatures, the physical control method utilizing elevated temperatures emerges as a viable alternative to chemical insecticides for controlling stored-products moths and beetles. This method holds promise and can be incorporated into pest management programs targeting these particular pests.